摘要:

THE ROYAL SOCIETY OF CHEMISTRY Journal of the Chemical Society Faraday Transactions Scientific Editor Dr. Peter J. Sarre Department of Chemistry University of Nottingham University Park Nottingham NG7 2RD, UK Faraday Editorial Board Prof. I. W. M. Smith (Birmingham) (Chairman) Prof. M. N. R. Ashfold (Bristol) Dr. B. E. Hayden (Southampton) Dr. D. C. Clary (Cambridge) Prof. A. R. Hillman (Leicester) Dr. L. R. Fisher (Bristol) Prof. J. Holzwarth (Berlin) Prof. H. M. Frey (Reading) Dr. P. J. Sarre (Nottingham) Dr. R. K. Thomas (Oxford) Editorial Manager and Secretary to Faraday Editorial Board Dr. Robert J. Parker The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF, UK Senior Assistant Editors: Mrs.S. Shah, Dr. R. A. Whitelock Assistant Editor: Mrs. C. J. Seeley Editorial Secretary: Mrs. J. E. Gibbs International Advisory Editorial Board R. S. Berry (Chicago) Y. Marcus (Jerusalem) A. M. Bradshaw (Berlin) B. J. Orr (North Ryde) A. Carrington (Southampton) R. H. Ottewill (Bristol) M. Che (Paris) R. Parsons (Southampton) M. S. Child (Oxford) S. L. Price (London) B. E. Conway (Ottawa) F. Rondelez (Paris) G.R. Fleming (Chicago) J. P. Simons (Oxford) R. Freeman (Cambridge) S. Stoke (Amsterdam) H. L. Friedman (Stony Brook) J. Troe (Gottingen) H. lnokuchi (Okazaki) J. Wolfe (Kensington, NSW) J. N. lsraelachvili (Santa Barbara) C. Zannoni (Bologna) M. L. Klein (Philadelphia) A. Zecchina (Turin) R.A. Marcus (Pasadena) C. Zhang (Dalian) Journal of the Chemical Society, faraday Transactions (ISSN 0956-5000) is published twice monthly by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. All orders accompanied with payment should be sent directly to The Royal Society of Chemistry, Turpin Distribution Services Ltd., Black- horse Road, Letchworth, Herts. SG6 1 HN, UK. NB Turpin Distribution Services Ltd., dis- tributors, is wholly owned by the Royal Society of Chemistry. 1994 Annual subscription rate EC €744.00, Rest of World f800.00,USA $1400.00. Canada f840 (excl. GST). Customers should make payments by cheque in sterling payable on a UK clearing bank or in US dollars payable on a US clearing bank. Second class postage is paid at Rahway, NJ.Airfreight and mailing in the USA by Mercury Airfreight International Ltd. Inc., 2323 Randolph Avenue, Avenel, NJ 07001, USA and at additional mailing offices. USA Postmaster: send address changes to Journal of the Chemical Society, faraday Trans- actions, c/o Mercury Airfreight International Ltd. Inc., 2323 Randolph Avenue, Avenel, NJ 07001. All despatches outside the UK by consolidated Airfreight. PRINTED IN THE UK. @ The Royal Society of Chemistry, 1994. All rights reserved. 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Full details of the form of manuscripts for Articles and Faraday Communications, con- ditions for acceptance etc. are given in issue number one of faraday Transactions, published in January of each year, or may be obtained from the Editorial Manager. There is no page charge for papers published in faraday Transactions. Fifty reprints are supplied free of charge. Dr. P. J. Sarre, Scientific Editor. Tel. : Nottingham (0602) 51 3465 (24 hours) E- Mail (JANET): PCZPSF@,UK.AC.NOlT.VAX Fax: (0602) 513466 Telex : 37346 U NINOT G Dr. R. J. Parker, Editorial Manager. Tel. : Cambridge (0223) 420066 E- Mai I (I NTER N ET) : RSCl @RSC.ORG (For access from JANET use RSCl %RSC.ORG@UK.AC.NSF NET-R ELAY) Fax : (0223) 423623 or 420247 Telex: 81 8293 ROYAL G

ISSN:0956-5000    

DOI:10.1039/FT99490FX029

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Editors: R E Hester, Universityof York, UK R M Harrison, University of Birmingham, UK A new series to tackle imporfanf environmental issues. .. In response to the rapid rowth of interest in the environment and t7le acute need for concise, authoritative and up-to-date reviews of topical issues, the Royal Society of Chemistry is launching Issues in Environmental Science and Technology. This new series will publish review articles on to ics of global concern, written b worl8experts in their specialized fie1 cys. It will present a multidisciplinary approach to pollution and environmental science and in addition to covering the chemistry of environmental processes, will focus on broader issues such as economic, legal and political considerations. Issues in Environmental Science and Technology will review the effects on human and non-human biota of man-made substances and will provide assessments of the possible practical solutions to perceived environmental problems, including the worldwide efforts currently underway to establish ‘Clean Tech no logies’.Who will be reading Issues in Environmental Science and Technology? ‘Issues’ will prove invaluable for scientists and engineers in industry, public service, consultancy and academic institutions, who wish to keep up-to-date on topical subjects in this emotive field. It will also be essential reading for students taking specialized courses in environmenta chemistry and will provide excellent supplementary reference material for general science courses.Each issue will address a different theme and will contain approximately six articles, most of which will be specially commissioned by the editors. The first two issues will cover: ISBN 0 85404 200 8 April 7994 Price f15.00 Also Available ISSN 1350-7583 on subscription. .. EC f25.00 USA $47.00 II I 0956-50001199438;l-0 i ROYAL SOCIETY OF CHEMISTRY 7&& Information Services Waste Incineration 2 and the Environment ISBN 0 85404 205 9 July 7994 Price f75.00 Published twice yearly from 1994 Canada f28.00+ GST Rest of World f27.00 To order please contact: Turpin Distribution Services Ltd, Blackhorse Road, Letchworth Herts SG6 1HN, United Kingdom Tel: +44 (0)462 672555. Fax: +44 (0)462 480947 RSC Members should order from: Membership Administration, Royal Society of ChemistryThomas Graham House, Science Park, Milton Road Cambridge CB4 4WF, United Kingdom Tel: +44 70)223 420066. Fax: +44’ (0)223 423623

ISSN:0956-5000    

DOI:10.1039/FT99490BX031

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

ISSN 0956-5000 JCFTEV(8) 1055-1196 (1994) JOURNAL OF THE CHEMICAL SOCIETY Faraday Transactions Physical Chemistry & Chemical Physics CONTENTS 1055 High-resolution FTIR-jet spectroscopy of CCl,F, D. McNaughton, D. McGilvery and E.G. Robertson 1061 Clusters of c6, molecules D. J. Wales 1065 Fourier-transform luminescence spectroscopy of solvated singlet oxygen A. N. Macpherson, T. G. Truscott and P.H. Turner 1073 Photophysical studies of substituted porphyrins P. Charlesworth, T. G. Truscott, D. Kessel, C. J. Medforth and K. M. Smith 1077 Model calculations of chemical interactions. Part 7.-Role of vicinal delocalization in the regiochemical control of the cycloaddition of diazomethane and formonitrile oxide to methyl vinyl ether A. Rastelli, M.Bagatti, R. Gandolfi and M. Burdisso 1083 Excess volumes of the ternary mixtures butylamine-cyclohexane-benzene and tributylamine-cyclohexane-benzene S. L. Oswal and S. G. Patel 1089 Dielectric behaviour of the N,N-dimethylformamide-2-methoxyethanol-l,2-dimethoxyethaneternary solvent system from -10 to +20 "C F. Corradini, A. Marchetti, M. Tagliazucchi, L. Tassi and G. Tosi 1095 Active site of bacteriorhodopsin. FTIR and 'HNMR studies using a model molecule B. Brzezinski, J. Olejnik and G. Zundel 1099 'H NMR relaxation time studies of the hydration of the barley protein C-hordein P.S.Belton, A. M. Gil and A. Tatham 1105 Mechanism of bleaching by peroxides. Part 3.-Kinetics of the bleaching of phenolphthalein by transition-metal salts in high pH peroxide solutions K.M. Thompson, W. P.Griffith and M. Spiro 1115 Dual transmission line with charge-transfer resistance for conducting polymers W. J. AIbery and A. R. Mount 1121 Electropolymerisation of indole-5-carboxylic acid J. G. Mackintosh and A. R. Mount 1127 Solid-state conductivities of CPQ [l,l'-bis(p-cyanophenyl)-4,4-bipyridilium]salts, redox-state mixtures and a new intervalence adduct D. R. Rosseinsky and P.M. S. Monk 1133 Brownian dynamics simulations of concentrated dispersions : Viscoelasticity and near-Newtonian behaviour D. M. Heyes, P. J. Mitchell, P.B. Visscher and J. R. Melrose 1143 Relaxation and crystallisation of water in a hydrogel K. Pathmanathan and G. P. Jobari 1149 Rotational excitations of NHZ ions in dilute solutions in alkali-metal halide lattices R.Mukhopadhyay, B. A. Dasannacharya, J. Tomkinson, C. 1.Carlile and J. Gilchrist 1153 Adsorption in energetically heterogeneous slit-like pores : Comparison of density functional theory and computer simulations G. Chmiel, L. tajtar, S. Sokdowskiand A. Patrykiejew 1157 Characterization of supported-palladium catalysts by deuterium NMR spectroscopy T-h. Chang, C. P.Cheng and C-t. Yeh 1161 Spectroscopic characterization of magnesium vanadate catalysts. Part 1.-Vibrational characterization of Mg3(V0,), , Mg2V20, and MgV206 powders G. Busca, G. Ricchiardi, D. S. H. Sam and J-C. Volta 1171 Mossbauer study of oxygen-deficient Zn"-bearing ferrites (Zn,Fe3-,04-a, 0 < x < 1) and their reactivity toward C02 decomposition to carbon M.Tabata, K. Akanuma, T. Togawa, M. Tsuji and Y. Tamaura 1117 Activation of surface lattice oxygen in the oxidation of carbon monoxide on silica Y. Matsumura, J. B. Mofht and K. Hashimoto 1183 Oxidation of carbon monoxide on LaMn, -,Cu,O3 perovskite-type mixed oxides H. Yasuda, Y. Fujiwara, N. Mizuno and M. Misono 1191 Inelastic neutron scattering study of NH,Y zeolites W. P. J. H. Jacobs, R. A. van Santen and H. Jobic Note: Where an asterisk appears against the name of one or more of the authors, it is included with the authors' approval to indicate that correspondence may be addressed to this person. COPIES OF CITED ARTICLES The Royal Society of Chemistry Library can usually supply copies of cited articles. For further details contact: The Library, Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN, UK Tel: +44 (0)71-437 8656 Fax: +44 (0)71-287 9798 Telecom Gold 84: BUR210 Electronic Mailbox (Internet) LIBRARY @RSC.ORG. If the material is not available from the Society’s Library, the staff will be pleased to advise on its availability from other sources. Please note that copies are not available from the RSC at Thomas Graham House, Cambridge.

ISSN:0956-5000    

DOI:10.1039/FT99490FP075

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Cumulative Author Index 1994 Aas,N., 1015 Carlsen, L., 941 Gill, J. B., 315 Kim, J-H., 377 Moriguichi, I., 349 Afanasiev, P., 193 Carvill, B. T., 233 Goede, S. J., 327 King, F., 203 Morikawa, A., 377 Aikawa, M., 911 Catalina, F., 83 Gomez, C. M., 339 Kirschner, J., 403 Morokuma, M., 377 Aitken, C. G., 935 Cavasino, F. P., 311 Goncalves da Silva, A. M., Kita, H., 803 Morrison, C. A., 755 Akanuma, K., 1171 Chang, T-h., 1157 649 Klein, M. L., 253 Mount, A. R., 1115, 1121 Akolekar, D. B., 1041 Charlesworth, P., 1073 Gray, P. G., 369 Kleshchevnikova, V. N., Muir, A. V. G., 459 Albery, W. J., 11 15 Chen, J-S., 429, 717 Green, W. A., 83 629 Mukherjee, T., 711 Aldaz,A., 609 Chen, Y-H., 617 Grein, F., 683 Kobayashi, A., 763 Mukhopadhyay, R., 1149 Alfimov, M. V., 109 Cheng, A., 253 Griffith, W.P., 1105 Kobayashi, H., 763 Nagaishi, R., 93, 591 Al-Ghefaili, K. M., 383, Cheng, C. P., 1157 Grimshaw, J., 75 Kobayashi, T., 101 1 Nagaoka, H., 349 1047 Cherqaoui, D., 97 Grzybowska, B., 895 Kondo, Y., 121 Naito, S., 899 Ali, V., 579, 583 Chesta, C. A., 69 Guelton, M., 895 Kossanyi, J., 411 Naito, T., 763 Allegrini, P., 333 Chevalier, S., 667,675 Gulliya, K. S., 953 Kurrat, R., 587 Navaratnam, S., 83 Allen, N. S., 83 Chmiel, G., 1153 Hachey, M., 683 Kuwamoto, T., 121 Neoh, K. G., 355 Al Rawi, J. M. A., 845 Cho,T., 103 Haeberlein, M., 263 Laachir, A,, 773 Nerukh, D. A., 297 Amorim da Costa, A. M., Christensen, P., 459 Hall, D. I., 517 Lajtar, L., 1153 Nicholson, D., 181 689 Climent, M. A., 609 Hall, G., 1 Lambert, J-F., 667,675 Nickel, U., 617 Amoskov, V.M., 889 Coates, J. H., 739 Hallbrucker, A,, 293 Lamotte, J., 1029 Ninomiya, J., 103 Ando, M., 1011 Cordischi, D., 207 Halpern, A., 721 Langan, J. R., 75 Nishihara, H., 321 Andrews, S. J., 1003 Corna,A., 213 Hamnett, A., 459 Lavalley, J-C., 1023, 1029 Nogami, T., 763 Aragno, A., 787 Cornier, G., 755 Hancock, G., 523 Lavanchy, A., 783 Nonaka, O., 121 Aramaki, K., 321 Corradini, F., 859, 1089 Handa, H., 187 Lazzarini, E., 423 Nuiiez Delgado, J., 553 Aravindakumar, C. T., 597 Corrales, T., 83 Hann,K., 733 Leaist, D. G., 133 Nyholm, L., 149 Asai, Y ., 797 Cosa, J. J., 69 Hao, L., 133 Lei, G-D., 233 Occhiuzzi, M., 207,905Avila, V., 69 Cottier, D., 1003 Harada, S., 869 Lerner, B. A., 233 Ohtsu, K., 127 Baba,T., 187 Coudurier, G., 193 Haraoka, T., 911 Leslie, M., 641 Okamura, A., 803 Badri, A., 1023 Courcot, D., 895 Harland, P.W., 935 Li, J., 39 Olejnik, J., 1095 Bagatti, M., 1077 Crawford, M. J., 817 Harper, R. J., 659 Li, P., 605 Oliveri, G., 363 Ball, M. C., 997 Cullis, P. M., 727 Harriman, A., 697,953 Li, Y., 947 Onishi, T., 9 11 Ball, S. M., 523 Curtis, J. M., 239 Harrison, N. J., 55 Lin, J., 355 Ono,Y., 187 Barbaux, Y., 895 Dang, N-T., 875 Haruta, M., 1011 Lincoln, S. F., 739 Oradd, G., 305 Barthomeuf, D., 667,675 Danil de Namor, A. F., 845 Hashimoto, K., 1177 Lindblom, G., 305 Ortica, F., 279 Basini, L., 787 Das, T. N., 963 Hashino, T., 899 Liu, C-W., 39 Oswal, S. L., 1083 Bassoli, M., 363 Dasannacharya, B. A., 1149 Hattori, H., 803 Liu,X., 249 Ota, K-i., 155 Battaglini, F., 987 Davey, R.J., 1003 Heal, M. R., 523 Loginov, A. Yu., 219,227 Otlejkina, E. G., 297 Bauer, C., 517 Davidson, K., 879 Heenan, R. K., 487 Lohse, U., 1033 Otsuka, K., 451 Bell, A. J., 17, 817 Demeter, A., 41 1 Helmer, M., 31, 395 Longdon, P. J., 315 Ottavi, G., 333 Belton, P. S., 1099 Dempsey, P., 1003 Herein, D., 403 Lu, J-X., 39 Ouellette, D. C., 837 Bendig, J., 287 Demri, D., 501 Herzog, B., 403 Lunelli, B., 137 Owari, T., 979 Bengtsson, L. A., 559 Derrick, P. J., 239 Heyes, D. M., 1133 Mabuchi, M., 899 Ozutsumi, K., 127 Benko, J., 855 Dewing, J., 1047 Higgins, S., 459 Machado, V. G., 865 Padley, M. B., 203 Benniston, A. C., 953 Diagne, C., 501 Hindermann, J-P., 501 Mackie, J. C., 541 Pal, H., 711 Bensalem, A., 653 Dickinson, E., 173 Hirst, D.M., 517 Mackintosh, J. G., 1121 Palleschi, A., 435 Berces, T., 41 1 Doblhofer, K., 745 Hiyane, I., 973 Macpherson, A. N., 1065 Paradisi, C., 137 Bergeret, G., 773 Domen, K., 91 1 Hoekstra, D., 727 Maeda,T., 899 Pardo,A., 23 Bickelhaupt, F., 327 Doughty, A., 541 Holmberg, B., 559 Maestre, A., 575 Parsons, B. J., 83 Biczok, L., 41 1 Douglas, C. B., 471 Holz, M., 849 Maginn, S. J., 1003 Patel, S. G., 1083 Binet, C., 1023 Dwyer, J., 383, 1047 Hoshino, H., 479 Mahy, J. W. G., 327 Pathmanathan, K., 1143 Black, S. N., 1003 Dyke, J. M., 17 Hosoi, K., 349 Maity, D. K., 703 Patrykiejew, A., 1153 Blackett, P. M., 845 Eastoe, J., 487 Hutchings, G. J., 203 Makarova, M. A., 383, Pavanaja, U. B., 825 Blandamer, M. J., 727 Easton, C.J., 739 Hutton, R. S., 345 1047 Pedulli, G. F., 137 Blower, C., 919,931 Ebitani, K., 377 Ikawa, S-i., 103 Maksymiuk, K., 745 Peeters, M. P. J., 1033 Boggis, S. A., 17 Egsgaard, H., 941 Ikonnikov, I. A., 219 Malatesta, V., 333 Peng, W., 605 Borisenko, V. N., 109 El-Atawy, S., 879 Indovina, V., 207 Malcolm, B. R., 493 Pepe,F., 905 Boutonnet-Kizling, M., Elisei, F., 279 Inoue, Y., 797, 815 Mallon, D., 83 Pereira, C. M., 143 1023 Elliot, A. J., 831, 837 Ishiga, F., 979 Mandal, A. B., 161 Perez, J. M., 609 Bowker, M., 1015 Engberts, J. B. F. N., 727 Ishigure, K., 93, 591 Marcheselli, L., 859 Perrichon, V., 773 Bozon-Verduraz, F., 653 Eustaquio-Rincon, R., 113 Isoda, T., 869 Marchetti, A., 859, 1089 Peter, L. M., 149 Bradley, C. D., 239 Ewins, C., 969 Ito, O., 571 Mariani, M., 423 Petrov, N.Kh., 109 Bradshaw, A. M., 403 Fantola Lazzarini, A. L., Iwasaki, K., 121 Martins, A., 143 Pispisa, B., 435 Braun, B. M., 849 423 Jacobs, W. P. J. H., 1191 Maruya, K-i., 911 Pivnenko, N. S., 297 Breysse, M., 193 Fausto, R., 689 Jakubov, T., 783 Masetti, F., 333 Plane, J. M. C., 31, 395 Briggs, B., 727 Favaro, G., 279,333 Jameel, A. T., 625 Massucci, M., 445 Plowman, R., 1003 Brocklehurst, B., 271 Feliu, J. M., 609 Janchen, J., 1033 MatijeviC, E., 167 Porcar, I., 339 Brown, R. G., 59 Filimonov, I. N., 219, 227 Jayakumar, R., 161 Matsuda, J., 321 Potter, C. A. S., 59 Brown, S. E., 739 Fogden, A., 263 Jenneskens, L. W., 327 Matsumura, Y., 1177 Poyato, J. M. L., 23 Bruna, P. J., 683 Fornes, V., 213 Jennings, B.J., 55 May, I. P., 751 Prenosil, J. E., 587 Brzezinski, B., 843, 1095 Franck, R., 667,675 Jiang, P-Y., 591 Mazzucato, U., 333 Previtali, C. M., 69 Buckley, A. M., 1003 Freeman, N. J., 751 Jiang, P. Y., 93 McGilvery, D., 1055 Pringle, T. J., 1015 Burdisso, M., 1077 Frkty, R., 773 Jobic, H., 1191 Mchedlov-Petrossyan, N. O., Priyadarsini, K. I., 963 Busca, G., 1161 Frey, J. G., 17, 817 Johansson, L. B.-& 305 629 Pryamitsyn, V. A., 889 Butt, M. D., 727 Frostemark, F., 559 Johari, G. P., 883, 1143 McNaughton, D., 1055 Rabold, A., 843 Byatt-Smith, J. G., 493 Fujiwara, Y., 1183 Joseph, E. M., 387 Medforth, C. J., 1073 Rama Rao, K. V. S., 825 Cabaleiro, M. C., 845 Gandolfi, R., 1077 Joshi, P. N., 387 Melrose, J. R., 1133 Ramsden, J. J., 587 Caceres Alonso, M., 553 Gans, P., 315 Kagawa, S., 349 Merga, G., 597 Rao, B.S. M., 597 Calado, J. C. G., 649 Gao, Y., 803 Kaler, E. W., 471 Meunier, F., 369 Rastelli, A,, 1077 Caldararu, H., 213 Garcia, R., 339 Kalugin, 0.N., 297 Mezyk, S. P., 831 Rehani, S. K., 583 Calvente, J. J., 575 Garcia Baonza, V., 553 Kato, R., 763 Misono, M., 1183 Rettig, W., 59 Calvo, E. J., 987 Garcia-Paiieda, E., 575 Katsumura, Y., 93,591 Mitchell, P. J., 1133 Rey, F., 213 Camacho, J. J., 23 Gautam, P., 697 Kaur,T., 579 Mittal, J. P., 597, 703, 7 11, Rezende, M. C., 865 Cameron, B. R., 935 Geantet, C., 193 Kawashima, T., 127 825 Rhodes, N. P., 809 Campa, M. C., 207 Gengembre, L., 895 Keil, M., 403 Miyake, Y., 979 Ricchiardi, G., 1161 Campos, A., 339 Gil, A. M., 1099 Kemball, C., 659 Mizuno, N., 1183 Richter, R., 17 Capobianco, J.A., 755 Gil, F. P. S. C., 689 Kessel, D., 1073 Moffat, J. B., 1177 Robertson, E. G., 1055 Caragheorgheopol, A,, 213 Gilchrist, J., 1149 Kida, I., 103 Mohan, H., 597,703 Rocha, M., 143 Carlile, C. J., 1149 Gill, D. S., 579, 583 Kiennemann, A,, 501 Monk, P. M. S., 1127 Rochester, C. H., 203 i Rodes, A., 609 Roffia, S., 137 Rosenholm, J. B., 733 Rosmus, P., 517 Rosseinsky, D.R., 1127 Rossi, P. F., 363 Rout, J. E., 1003 Rudham, R., 809 Ryde,N., 167 Sacco, A., 849 Sachtler, W. M.H., 233 Saitoh, T., 479 Salmon, G. A., 75 Sam, D.S.H., 1161 Sano,T., 869 Sapre, A. V., 825 Sarre, P. J., 517 Sato, K., 797 Saw, O., 1029 Sbriziolo, C., 3 11 Schedel-Niedrig, Th., 403 Schlogl, R., 403 Schnabel, W., 287 Scremin, M., 865 Seddon, B.J., 605 Shahid, G., 507, 513 Sharma, A., 625 Shaw, N., 17,817 Sheil, M.M., 239 Sheppard, N., 507,513 Shiao, J-C., 429 Shihara, Y., 549 Shiralkar, V. P., 387 Shishido, T., 803 Shizuka, H., 533 Siders, P., 973 Silva, C.J., 143 Silva, F., 143 Simkiss, K., 641 Singh, J., 579, 583 Singh, R., 583 Smith, K. M., 1073 Smith, T. D., 919,931 Soares, V. A. M., 649 Sokdowski, S., 1153 Soria,V., 339 Spiro, M., 617, 1105 Stanley, D.R., 1003 Stewart, B., 969 Stoeckli, F., 783 Sun, L.M., 369 Suquet, H., 667,675 Surov, Y. N., 297 Suzuki, T., 549 Tabata, M., 1171 Tabrizchi, M., 17 Tagliazucchi, M., 859, 1089 Takagi, T., 121 Takahashi, K., 155 Takasawa, A., 911 Tamaura, Y., 1171 Tamura, K-i., 533 Tanaka, I., 349 Tassi, L., 859, 1089 Tateno, A., 763 Tatham, A., 1099 Taylor, A., 1003 Taylor, M.G., 641 Teixeira-Dias, J.J. C., 689 Udagawa, T., 763 Umemoto, H., 549 Unayama, S-i., 549 Upadhyaya, H. P., 825 Valat, P., 411 Valls, M.J., 609 van Hooff, J. H. C., van Santen, R. A., 1191 van Wolput, J. H. M. C., 1033 Wikander, G., 305 Williams, D. E., 345 Wilpert, A., 287 Wintgens, V., 41 1 Woermann, D., 875 Wohlers, M., 403 Wolthuizen, J. P., 1033 Wormald, C. J., 445 Xin,Q., 973 Teo, W. K., 355 Teramoto, M., 979 Teraoka, Y., 349 Thompson, K. M., 1105 Thompson, N.E., 1047 Timms, A. W., 83 Timney, J. A., 459 Togawa, T., 1171 Tomkinson, J., 1149 Vedrine, J. C., 193 Venanzi, M., 435 Villamagna, F., 47 Villemin, D., 97 Visscher, P.B., 1133 Vlietstra, E.J., 327 Vollarovk O., 855 Vollmer, F., 59 1033 Yagci,Y., 287 Yamaji, M., 533 Yamamoto, M., 899 Yamanaka, I., 451 Yamasaki, M., 869 Yanes, C., 575 Yang, Z-Q., 947 Yano,H., 869 Yasuda, H., 1183 Tosi, G., 859, 1089 Touret, O., 773 Tournayan, L., 773 Trejo, A., 113 Truscott, T. G., 1065, 1073 Tsuji, H., 803 Tsuji, M., 1171 Tsunashima, S., 549 Tun& C-H., 947 Turco Liveri, M.L., 311 Turco Liveri, V., 31 1 Turner, P.H., 1065 Vyunnik, I. N., 297 Wales, D.J., 1061 Wang, C. F., 605 Watanabe, H., 571 Waters, M., 727 Weckstrom, K., 733 Weingartner, H., 849 Weir, D. J., 751 Werner,H., 403 Whitaker, B. J., 1 Whitehead, M.A., 47 Volt& J-C., 1161 Yeh, C-t., 1157 Yoshitake, H., 155 Yotsuyanagi, T., 93,479 Young, R. N., 271 Zanotto, S.P., 865 Zhang,X., 605 Zholobenko, V.L., 233, Zhong, G. M., 369 Ziolek, M., 1029 Zubarev, V. E., 721 Zundel, G., 843,1095 1047 The following papers were accepted for publication between 1st and 28th February 1994: Profiles of adsorption during the oxidation of small organic molecules: Oxidation of formic acid at polycrystalline Pt in acid solutions C. P. Wilde and M. Zhang Zinc-exchanged Y zeolites studied with carbon monoxide and xenon as probes B. Boddenberg and A. Seidel Solid-state ion exchange in zeolites. Part 5.-NH4-Y-iron (11) chloride H.G. Karge, K. Lazar, G. Pal-BorbCly and H.K. Beyer Properties of alkali-metal ion exchange of HP zeolite. Part 2.-Studies of adsorption of benzene on the acidic and basic sites of KHP zeolites by in situ IR J-P.Shen, J. Ma, T. Sun, D-Z. Jiang and E-Z. Min Study of the complexation and precipitation equilibria in the system Ni'143V'-H20 R. Castaiio, M.A. Olazabal, G. Borge and J.M. Madariaga Electronic transitions in metallocenes by resonance Raman scattering. Part 1 .-Analysis of the ferrocene spectrum in the visible region M.L. Ceccarani, P. Sassi and R.S. Cataliotti Molecular conformations and rotation barriers of 2-halogenoethanethiols and 2-halogenoethanols. An ab initio study G. Buemi Nature of hydrogen bonds formed by phenol derivatives and N,N-dimethylaniline in aprotic solvents: Low- temperature NMR studies M. Iicczyszyn Unsteady state, non-isothermal dissolution of a solid particle in liquid J-P. Hsu and B-T.Liu Investigation into the kinetics and mechanism of the reaction of NO, with CH, and CH,O at 298 K between 0.6 and 8.5 torr R.P. Wayne, P. Biggs, C.E. Canosa-Mas, J-M. Fracheboud and D.E. Shallcross Investigation into the kinetics and mechanism of the reaction of NO, with CH,O, at 298 K and 2.5 torr. A potential source of OH in the night-time troposphere P. Biggs, C.E. Canosa-Mas, J-M. Fracheboud, D.E. Shallcross and R.P. Wayne Comparison of DNA duplexes with and without 04-methylthymine: Nanosecond molecular dynamics simulations L. Cruzeiro-Hansson and J.M. Goodfellow Virial theorem decomposition as a guiding tool for comparing and improving potential-energy surfaces: Ground- state Li, A. J.C. Varandas, A.A.C.C. Pais and R.F. Nalewajski Comparison of the electrokinetic properties of the silica surface D.E.Dunstan Valence and core photoemission of the films formed electrochemically on nickel in sulfuric acid Y.Liang, D.K. Paul and P.M.A. Sherwood Integral equation theory for associating liquids: Highly asymmetric electrolytes A.D. J. Haymet and J. Wang Raman spectroscopic study of the PtXeO, interaction in the Pt/Al, 0,-Ce02 catalyst T.J. Dines, M.S. Brogan and J.A. Cairns Manganese-promoted rhodium/NaY zeolite catalysts. An IR spectroscopic study T. Beutel, H. Knozinger, H. Trevino, Z.C. Zhang, W.M.H. Sachtler, C. Dossi, R. Psaro and R. Ugo Rotational dynamics in liquid water: A simulation study of librational motions I.M. Svishchev and P.G. Kusalik Vibrational spectroscopic analysis of group 6 metal hexacarbonyls in the solid state U.A.Jayasooriya Characterisation of several y-alumina supported nickel catalysts and activity for selective hydrogenation of hexanedinitrile F. Medina, P. Salagre, J.E. Sueiras and J-L-G. Fierro Nickel incorporated into anodic porous alumina formed on an aluminium wire N. Ohji, N. Enomoto, T. Mizushima, N. Kakuta, Y. Morioka and A. Ueno Reduction of hexacyanoferrate (111) by thiosulfate ions mediated by ruthenium dioxide hydrate A. Mills, X. Li and G. Meadows Electrical properties of pure vanadium phosphate phases and of VPO catalyts used in the partial oxidation of n-butane to maleic anhydride J-M. Herrmann, F. Rouvet and J.C. Volta Conformational properties of monosubstituted cyclohexane guest molecules constrained within zeolite host materials: A solid-state NMR investigation A.E.Aliev, K.D.M. Harris and R.C. Mordi ... 111 Thennophysical properties of liquid m-xylene at high pressures V.G. Baonza, M. Taravillo, S. Castro, M. Caceres and J. Nunez Heats of transport of aqueous tetraalkylammonium hydroxides and the electrophoretic effect D.G. Leaist and L. Hao Rotational spectrum of the gas-phase dimer OC-BrC1 A.C. Legon, S. Blanco Rodriguez and J.C. Thorn [(q2-C,H,)Os(CO),] as a vibrational model for type I’ ethene chemisorbed as a metallacyclopropane on metal surfaces C.E. Anson, N. Sheppard, D.B. Powell, B.R. Bender and J.R. Norton Clusters of C, molecules D.J. Wales iv FARADAY DIVISION INFORMAL AND GROUP MEETINGS Statistical Mechanics and Thermodynamics Group Cellular Automata and their Applications to Molecular Fluids To be held at the University of Manchester on 19 and 20 July 1994 Further information from Dr A.Masters, Department of Chemistry, University of Manchester, Manchester M13 9PL Division Autumn Meeting: Reactions and Mechanisms for Fine Chemicals To be held at the University of Glasgow on 6-9 September 1994 Further information from Dr J. F. Gibson, The Royal Society of Chemistry, Burlington House, London W1V OBN Gas Kinetics Group 13th International Symposium on Gas Kinetics To be held at University College, Dublin on 11-15 September 1994 Further information from Dr H. Sidebottom, Department of Chemistry, University College, Dublin Electrochemistry Group with the SCI ELECTROCHEM 94 To be held in Edinburgh on 12-16 September 1994 Further information from Professor D.E. Williams, Department of Chemistry, University College London, 20 Gordon Street, London WClH OAJ ~ Biophysical Chemistry Group with the Industrial Division Biotechnology Group Peptide + Water = Protein To be held at University College, London on 19 September 1994 Further information from Professor J. L. Finney, Department of Physics and Astronomy, University College London, Gower Street, London WClE 6BT ~~ British Carbon Group Applications of Microporous Carbons To be held at the University of Leeds on 28 and 29 September 1994 Further information from Professor B. Rand, Department of Chemistry, The University, Leeds LS2 9JT ~ Theoretical Chemistry Group with CCPl Electronic Structure: From Molecules to Enzymes To be held at University College London on 30 November 1994 Further information from Dr P.J. Knowles, School of Chemistry, University of Sussex, Falmer, Brighton BN1 9QJ Division Annual Congress: Lasers in Chemistry To be held at Heriot Watt University, Edinburgh on 10-13 April 1995 Further infomation from Dr J. F. Gibson, The Royal Society of Chemistry, Burlington House, London W1V OBN Division Joint Meeting with the Division de Chimie Physique de la Societe' Francaise de Chimie, Deutsche Bunsen Gesellschafi fur Physikalische Chemie and Associazione Italiana di Chimica Fisica Fast Elementary Processes in Molecular Systems To be held at the UniversitC De Lille, France on 16-30 June 1995 Further information from Dr C.Troyanowsky, Division de Chimie Physique, Laboratoire de Chimie Phvsiaue, 11 rue Pierre et Marie Curie, 75005 Paris, France British Carbon Group Carbon '96 To be held at the University of Newcastle upon Tyne on 7-12 July 1996 Further information from Dr K. M. Thomas, Northern Carson Research Laboratories, The University, Newcastle upon Tyne NE1 7RU V THE ROYAL SOCIETY OF CHEMISTRY, FARADAY DIVISION, GENERAL DISCUSSION 98 Polymers at Surfaces and Interfaces University of Bristol, 12-14 September 1994 Organising Committee: Professor Sir Sam Edwards (Chairman) Dr R. Buscall Professor R. H. Ottewill Dr T. Cosgrove Professor J.S. Higgins Dr R. W. Richards Dr R. A. L. Jones New experimental methods and new theoretical and computational techniques have recently led to great progress in understanding the difficult but technologically important problems associated with the conformation of polymer molecules at surfaces and interfaces. The purpose of this Discussion is to bring together experimentalists and theoreticians working towards a molecular understanding of polymers at surfaces and interactions to survey the progress in the area to date and to indicate future directions of research. The meeting will attempt to bring a unified approach to the problem, encompassing problems of the structure of surfaces and interfaces in polymer melts, the conformation of polymers at solid/liquid and liquid/liquid interfaces, and extensions towards more complicated biological systems.The preliminary programme may be obtained from Mrs Angela Fish, The Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN. THE ROYAL SOCIETY OF CHEMISTRY, FARADAY DIVISION, GENERAL DISCUSSION 99 Vibrational Optical Activity: from Fundamentals to Biological Applications University of Glasgow, 19-21 December 1994 Organising Committee Professor L. D. Barron (Chairman) Dr A. F. Drake Dr D. L. Andrews Professor R. E. Hester Professor A. D. Buckingham Traditional optical activity measurements such as CD are confined to the visible and near-ultraviolet spectral regions where they provide stereochemical information on chiral molecules via polarized electronic transitions.Thanks to prompting from theory and new developments in instrumentation, optical measurements are now being made in the vibrational spectrum using both infrared and Raman methods. Studies over the past decade on a large range of chiral molecules, from small organics to biological macromolecules, have demonstrated that vibrational optical activity opens up a whole new world of fundamental studies and practical applications undreamt of in the realm of conventional electronic optical activity. The meeting seeks to bring together experimentalists and theoreticians to discuss the current and future experimental possibilities and the development of theories, including ab initio computational methods, which can relate the observations to stereochemical details.The increasing importance now being attached to molecular chirality and solution conformation in the life sciences should also encourage the partipation of biomolecular scientists. The preliminary programme may be obtained from Mrs Angela Fish, The Royal Society of Chemistry, Burlington House, London W 1V OBH. vi THE ROYAL SOCIETY OF CHEMISTRY, FARADAY DIVISION, GENERAL DISCUSSION 100 Atmospheric Chemistry: Measurements, Mechanisms and Models University of East Anglia, Norwich, 19-21 April 1995 Organising Committee: Professor I. W. M. Smith and Dr J. R. Sodeau (Co-chairmen) Dr R. A. Cox Dr J. C. PIane Dr J. Pyle Professor F. Taylor The priority now given by national governments to the study of atmospheric science confirms that our understanding of global climate and compositional changes depends upon measurements in both the laboratory and the field.The data obtained by the experimentalists are then applied by modellers who provide the most significant input into legislative controls on pollution matters. However there have been few opportunities for laboratory and field workers along with the modelling community to attend an "interdisciplinary" discussion in which overall progress in our understanding of specific atmospheric problems is assessed. The object of this discussion is to bring together the researchers in the diverse disciplines that make up atmospheric chemistry so that their individual results and conclusions can be communicated to each other.Some of the key issues to be discussed will include: ozone balances in the atmosphere; heterogeneous processes; the interaction of chemistry and dynamics in determining atmospheric composition and change. Particular reference will be made to the input of data to global models from the use of satellite, airborne and ground-based instrumentation. Contributions are invited for consideration by the Organising Committee covering topics within the area of chemistry, dynamics and modelling in the lower and upper atmosphere. Abstracts of about 300 words should be submitted by 31 May 1994 to: Professor I. W. M. Smith OR Dr R. J. Sodeau School of Chemistry School of Chemical Sciences University of Birmingham University of East Anglia Edgbaston, Birmingham Nonvich BIS 27T, UK NR4 7TJ, UK Full papers for publication in the Discussion volume will be required by December 1994.THE ROYAL SOCIETY OF CHEMISTRY, FARADAY DIVISION, GENERAL DISCUSSION 101 Gels Paris, France, 6-8 September 1995 Organising Committee: Dr J. W. Goodwin (Chairman) Dr R. Audebert Dr R. Buscall Professor M. Djabourov Dr A. M. Howe Professor J. Livage Professor J. Lyklema Professor S. B. Ross-Murphy During the last few years there has been an increase in both theoretical and experimental work on gels as new techniques have been applied to a wide range of gelling systems. Typical of these are gels formed from polymers by both physical and chemical interactions as well as gels formed by inorganic and surfactant systems.The meeting will deal with the structure and dynamics of gels with the latter heading covering both swelling and rheological behaviour. Mixed systems such as polymer/surfactant and polymer/particle gels will also be discussed. The Discussion will bring together experimentalists and theoreticians interested in different types of gelling systems and encourage them to interact and assess the current scene and provide a benchmark for future developments. Contributions are invited for consideration by the Organising Committee. Titles and abstracts of about 300 words should be submitted by 30 September 1994 to: Dr J. W. Goodwin, School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 ITS, UK Full papers for publication in the Faraday General Discussion 101 volume will be required by May 1995.vii The Royal Society of Chemistry Younger Chemists Committee Pre-Doctoral Chemistry Symposium 1994 Autumn Meeting, University of Glasgow 6th September 1994 CALL FOR PAPERS The Younger Chemists Committee are organising a Pre-Doctoral Symposium as part of the RSC’s Autumn Meeting, to be held at The University of Glasgow from 6-9th September 1994, There will be four parallel sessions for oral presentations, plus a poster session, reflecting the themes adopted by the following Divisional symposia at the Autumn Meeting:- Analytical:-Analytical Challenges in Toxicology and PollutionI Dalton:-Diversity in Co-ordination Chemistry Faraday & Macro:-Reactions and Mechanisms for Fine Chemicals in Heterogeneous Catalysis, The Organic and Physical Chemistry of Macromolecules, Perkin:-Organic Chemistry: Synthesis and Mechanisms, Postgraduate and young industrial chemists, aged under 30, are invited to submit abstracts for consideration as oral or poster presentations, Participants whose contributions are accepted will not be expected to pay the registration fee of €20, Papers covering topics not included in the theme of the Autumn Meeting are equally welcome for consideration, Anyone wishing to contribute a paper or poster, should submit a title and abstract (ca, 100 words) as soon as possible to:-Dr John F Gibson Sec re t ary (Scientific) m The Royal Society of Chemistry Burlington House London W1 V OBN Tel:- 071-437 8656 Organised in conjunction with the West of Scotland Section of The Royal Society of Chemistry ... Vlll

ISSN:0956-5000    

DOI:10.1039/FT99490BP077

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

1055J. CHEM.SOC. FARADAY TRANS., 1994, 90(8), 1055-1060 High-resolution FTIR-Jet Spectroscopy of CCI,F, Don McNaughton,* Don McGilvery and Evan G. Robertson Centre for High Resolution Spectroscopy and Optoelectronic Technology, Department of Chemistry, Monash University, Wellington Road, Clayton, Victoria, Australia 3 168 An experimental system employing a cryopump has been assembled for high-resolution FTIR spectroscopy of species cooled in a supersonic jet expansion. Coupled to a Bruker IFS 120HR interferometer, it involves an external sample chamber and transfer optics allowing 11 optical passes of the infrared beam. Tests with CO and N20 indicate rotational temperatures in the range 6-30 K. By heating the nozzle, significant population of vibra- tional states can be achieved without sacrificing rotational cooling.The mid-infrared spectrum of Freon-12, CC12F2, has been recorded and the v8 C-type band at 1161 cm-' analysed. Rotational constants for C3%12F2 and C37C135CIF, have been calculated and the rotational temperature estimated at 40 K. Introduction Supersonic Jet Spectroscopy The development of high-resolution FTIR spectrometers has greatly increased the capability to explore the vibration- rotation structure of molecules. The size and complexity of molecules amenable to study by FTIR techniques is limited by spectral congestion and the problem of assignment of overlapping transitions. Free expansion of gases in a super- sonic jet achieves significant cooling within the degrees of freedom of the molecules (Trans< T,,< qib).This relaxation greatly increases the population of molecules in lower rota- tional energy levels at the expense of higher energy levels.The advantages this has for spectroscopy include simplifica- tion of the spectrum and enhancement of the signal intensity of low J, K transitions. A wide variety of spectroscopic tech- niques have been used in conjunction with supersonic jets.' FTIR spectroscopy, with the advantage of broad spectral coverage, was first used to probe a supersonic expansion by Snavely et al.2-5 who recorded spectra at 0.06 cm-' resolution. Quack and co-workers developed the technique, using a Bomem spectrometer to study a variety of molecules at up to 0.004 an-' resolution.'*6-'6 Barnes et al.investi-gated molecular clusters in a molecular jet' 7*18and more recently other groups have made use of FTIR-jet spectros-copy to study semi-stable species," the CN radical produced in a corona discharge2' and other species., 1-24 Dichlorodifluorornethane(Freon-12) Freon-12, or CCl,F, ,is heavily used in industry as a refriger- ant, aerosol, sterilant and in plastic foams. Of great concern is its effect on the ozone layer. A stable molecule, it has a long lifetime, and is not broken down in the troposphere. In the higher stratosphere it undergoes photolysis by solar UV radi- ation, releasing chlorine atoms capable of catalysing the breakdown of ozone.25 Freon-12 is estimated to account for over 40% of ozone depletion.26 Extensive use has been made of infrared spectroscopy in the detection of atmospheric CCI,F, .27 The molecular constants obtained from high-resolution measurements are useful in modelling the tem- perature profiles of atmospheric pollutants like Freon- 12.Several microwave studies have been carried out on CCl,F, , resulting in accurately known ground-state con-stants for the three most abundant isotopic forms, C35C1,F,, C37C135C1F2 and C37C1,F, These forms occur in the approximate ratios (9 :6 : 1). C37C135C1F, has C, symmetry while the other two isotopic species belong to the C,, point group. The principal axis orientation for CCl,F, is shown in Fig. 1. Apart from intensity measurements and atmospheric studies, several infrared investigations have focussed on vibration-rotation structure.A medium-resolution (0.1 cm -I) band contour was followed by an analysis of the v6 and v8 Q branches, identifying fundamentals and hot bands for the two most abundant isotopic species.34 In another band contour study, hindered by insufficient resolution, incorrect conclusions about band types were drawn.3 The 923 cm-' v6 band of CCI,F, (asymmetric CCI, stretch) has been studied in some detail by infared-microwave double and by diode laser spectroscopy of the mol- ecules in a jet.27 A diode laser was also used to examine under high resolution the rovibrational structure of the 1101 cm-' v1 band of CCl,F, (symmetric CF, stretch) at 200 K.39 Some measurements of the Q branch heads of v8 have been made,40 also with a diode laser, but no vibration-rotation analysis of this band has been published.We report the development of a multi-pass transfer optic system for FTIR spectroscopy of jet-cooled species and the subsequent high-resolution spectral analysis of the v8 C-type band of CCl,F, (asymmetric CF, stretch) at 1161 an-'. Design and Experimental Our apparatus has undergone some modification since we first experimented with jet-cooled spectroscopy. The first design involved mounting a Varian HV12 cryopump hori- zontally to the side of the sample chamber of the Bruker IFS 120HR interferometer and positioning the nozzle inside the instrument's sample chamber so that the FTIR beam focussed in the cold region of the jet.Like Ballard et ~1 a .~~ cryopump was chosen for its cost effectiveness and reduced size in comparison with the more conventional oil diffusion pump, roots blower pump and backing pump combination. Unfortunately, with this arrangement, the mechanical vibra- tions associated with the pump coupled to the spectrometer optics and resulted in spectral artifacts and increased noise. For this reason it was necessary to run the instrument in purge mode with the cryopump uncoupled. Although the signal to noise ratios of the spectra of simple molecules obtained in this manner were adequate for diagnostics, the centre of mass b Fig. 1 Principal axis orientation for CCI,F, spectra of more complex molecules suffered from the inherent low sensitivity of FTIR spectroscopy.An external sample chamber and transfer optics box were then constructed in order to decouple the cryopump physically from the interfer- ometer and allow a multiple pass of the infrared beam through the cold-jet region. After some experimentation with a double-pass system, a mirror assembly was built to allow 11 passes. The apparatus, shown in Fig. 2,includes an air cushion pressurized to ca. 500 kPa, effectively damping out most of the mechanical vibra- tions associated with our cryopump. The entire external system is also vibrationally isolated from the interferometer by a flexible bellows. Circular pinhole nozzles were manufac- tured from 6 mm Pyrex glass tubing and may be heated to 550 K by a heating jacket.The mirrors transferring the beam out of the interferometer sample chamber are positioned to give a slight beam waist in order to maintain minimal beam diameter throughout the transfer optic system. All the trans- fer mirrors except two in the external chamber may be tilted vertically and horizontally. The final detector focussing mirror has a focal length of 33 mm, serving to focus the nearly parallel beam of ca. 25 mm diameter to a small region on the Judson Infrared inc HgCdTe-InSb detector. The jet nozzle chamber is isolated from the spectrometer, optics box and detector by a KBr window. Most of the test spectra of N20 and CO were collected using the initially designed internally positioned jet, with backing pressures of ca.300 kPa and nozzle diameters in the range 120-240 pm. The room-temperature spectrum of CCl,F2 at 0.01 m-' unapodized resolution was recorded using a pressure of 13 Pa in an Infrared Analysis Inc. multiple-pass cell with path- length set at 4 m. Jet-cooled spectra of CCl,F, were recorded at 0.0034 cm-' unapodized resolution using a 700-1300 cm-' filter. Nozzle height was set so that the nozzle just began to impinge on the IR beam, a position which was found to maximize signal absorption by the sample gas. Commercially available CC12F2 was used at a stagnation pressure of 600 kPa with an unheated 240 pm diameter nozzle, resulting in a flow rate that actually overloaded the cryopump. Therefore, it was necessary to isolate the cryo- pump from the sample gas for ca.45 min between sets of two to four scans so that the pressure measured in the lower part of the chamber did not exceed 0.1Pa. 80 scans were co-added in this way. This arrangement was chosen in order to maxi- mize sample density and hence absorption for the weak P and R structure of the v8 band. A total of ca. 1.5 kg of Freon- 12 was used over the 3 h of scanning time required for this experiment. Such large quantities are often required for experiments of this nature. For this reason our system includes the facility for a liquid-nitrogen trap between the cryopump and the backing pump to enable recycling of gases. Results and Discussion Performance Testing Preliminary testing with CO in the original single-pass chamber achieved rotational temperatures down to 6 K by seeding with argon.Temperatures were obtained from Boltz- mann plots of ln{(J + J' + 1);) us. E. Varying the distance of the focussed FTIR beam to nozzle aperture yielded results similar to those of Quack and co-workers,' and the minimum temperature was observed at a distance of around 12 mm for a 110 pm nozzle. Cooling for N20 was not as efficient. Spectra of the vJ band of N20 recorded under different con- ditions are shown in Fig. 3. Fig. 3(a)is a spectrum of pure N20, while the spectrum in Fig. 3(b) is of N20 diluted to 30% in argon. Rotational temperatures in the ground vibra- J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 -sample inlet nozzle height adjustmentnozzle horizontal position adjustment -L rotary pump compressed air detector I interaction external adjustment af vertical and bo horizontal slant for 1st and last mirror Fig.2 FTIR-Jet experimental apparatus. (a) Side view. H, 100 R, 10 W resistive heating jacket. B, Flexible bellows. T, x-y translation stage. (b) Top view. F1, 121 mm focal length off-axis parabolic reflec- tor. F2, 33 mm focal length off-axis paraboloid mounted on x-y translation stage. Ml-M4, plane mirrors. F1 and M2 are mounted on an x translation state. tional state for these two spectra are calculated to be 27.0& 2.1 and 19.7f0.8K,respectively. As may be seen by comparison of Fig. 3(a) and (b), dilution in argon assists in the cooling of N20, but at the expense of the signal-to-noise ratio.This enhanced cooling with argon dilution can be J. CHEM SOC. FARADAY TRANS 1994, VOL. 90 Q) C c s1n m t r 1 me s1n 2240 2230 2220 2210 2200 wavenurnber/cm-' Fig. 3 v3 band of N20 recorded with the first experimental appar- atus. (a) Pure N20 at 300 kPa backing pressure, 180 pm unheated nozzle, 0.01 cm-' resolution, five scans. (b) Same conditions as (a) except N20 diluted to 30% in Ar. (c) Pure N20 at 300 kPa backing pressure, 120 pm nozzle heated to 180°C, 0.05 cm-' resolution, 10 scans. attributed to more efficient collisional relaxation. The spec- trum in Fig. 3(c) is of neat N20 where the nozzle has been heated to ca. 450 K. The (0110)-(0111)hot band centred at 2209.5 cm-is clearly evident.The rotational temperature is calculated to be 20.7 f0.7 K in the ground vibrational state and 23.6 f0.5 K for the v2 = 1 excited vibrational state. It is clear that the final rotational temperature is not greatly increased by moderate heating of the nozzle. By contrast the vibrational temperature, calculated from the intensity of the hot-band transitions relative to the corresponding fundamen- tal transitions, is 488 f32 K.For the unheated nozzle in Fig. 3(a) a vibrational temperature of 204 f15 K is obtained, a result comparable to the value 213 f7 K obtained by Wall- raff et al. for OCS.41 These calculations are only approx- imate, in that they assume a Boltzmann-type vibrational population distribution, whereas the vibrational states are far from being in equilibrium.Not only do the translational, rotational and vibrational temperatures in molecules cool to different extents in a free expansion, but there is evidence that the extent of vibrational cooling depends on the nature of the ~ibration.~'A torsional mode, for example, appears to couple strongly with rotation and cools almost as efficiently as rota- tional degrees of freedom.22 When the observation is taken into account that in our system the unheated nozzles them- selves tend to cool to below 263 K, it is evident that the spectra of Fig. 3(a)and (c) show little evidence of substantial vibrational cooling. This clearly demonstrates the inefficiency of vibrational cooling in comparison with rotational cooling, while showing that some heating of the nozzle should prove advantageous for the study of rotationally cool hot bands.Dichlorodifluoromethane The room-temperature spectrum and jet-cooled spectrum of the 1161 cm-' C-type band of CCl,F, are shown in Fig. qa) and (b).Those Q branches which appear only in the room- temperature spectrum are from vibrational hot bands.36 Q, C +.It.-l fsi 2 Y ,1150 1160 117d',, 1180 ,' wavenurnber/crn-' '\, 1155 1160 1165 1170 wavenurnber/cm-' Fig. 4 (a) Room-temperature spectrum of CC12F, at 0.01 cm-' unapodized resolution. (b) Observed profile of the vg band of jet-cooled CC12F2 at 0.0034 cm- ' unapodized resolution. (c) Simulated band profile based on addition of the C35C12F, and C37C135C1F2 predictions at 40K.Their absence in the jet-cooled spectrum is evidence for some degree of vibrational cooling for this molecule. This is con- firmed by the observation that in the v6 region of the cool spectrum around 923 cm-' the only hot-band Q branches observed are from v4, the lowest-frequency fundamental. A section of the cool spectrum is shown in Fig. 5. Assignment of transitions was achieved through Macloomis, an interactive program which displays peaks in Loomis-Wood (Fortran) format.42 This technique is suc-cessful for regularly spaced series of transitions. Developed for the spectral analysis of linear and symmetric-top mol- ecules, it has also been applied to asymmetric tops near the symmetric limit such as vinylamine (IC= -0.93).43 Note that even for a molecule as asymmetric as CC12F2 (K = -0.57) regular structure exists for higher values of K,, as may be J.CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 series immediately above corresponds to PP, transitions of C3’C13’C1F2. Series are displayed with different colours to distinguish them easily from each other, an essential feature when assigning densely overlapped spectra like those shown. The separation between transitions within a series corre- sponds to ca. B+ C.Because of the small difference in rota- tional constants of the two isotopomers, their series appear at different angles in a Macloomis plot. This regular structure XI I I allows a relatively straightfoward assignment of transitions using Macloomis. Transitions that appeared overlapped on the Macloomis display or asymmetry doublets calculated to be split by more than O.OOO4 cm-’ were assigned an experi- mental uncertainty of 0.002 cm-’,otherwise an uncertainty of O.OOO4 cm-’ (10% of linewidth) was used in the weighted least-squares fit.Following the assignment of transitions using Macloomis, 1156.8 1157.0 1157.2 1157.4 1157.6 the data were transferred to an asymmetric rotor fitting waven urnber/crn-’ program. Watson’s A-reduced Hamilt~nian~~ was employed Fig. 5 Upper trace; Part of the V’ band of CCl,F,. Lower trace; and the ground-state constants held to those of ref. 32,simulated spectrum based on the C3’Cl,F, and C37C135C1F2 iso- resulting in the rotational and centrifugal distortion con-topes only.stants given in Table 1. The magnitudes of the standard devi- clearly seen from the Macloomis plot in Plate 1. The red pP16 ations of the fits are less than 1.0, indicating a good fit to the series (A& = -1, AJ = -1, K: = 16) of C3’C1,F, is dis- data. This implies that the constants will accurately repro- played vertically in the centre, while the dark-blue diagonal duce transition frequencies, which is important if the con- Table 1 Fitted rotational and distortion constants (in an-’)for the vg band of CCl,F, using Watson’s A-reduced Hamiltonian vibrational state parameter/cm -C3’C1,F, C37C1 ’ClF, Vob 1 16 1.08498 (4) 1160.96467 (6) A -Bb 0.05646622 (59) 0.05730849 (104) Bb 0.08 123097 (43) 0.07948650 (71) B -Cb 0.01353579 (266) 0.01326170 (438) A 0.13769719 0.13679499 B 0.08799886 0.0861 1735 C 0.07446307 0.07285565 A,b 1.308 (66) x lov8 1.424 (111) x lo-’ AJKb -1.109 (178) x lo-’ -9.45 (294) x 10-9 AKb 6.021 (145) x lo-’ 4.995 (265) x lo-’ 8,’ 3.649558 x lo-’ 3.519435 x 6,‘ 4.461253 x lo-’ 4.789547 x lo-’ ground state A 0.1373908212 0.1364949781 B 0.0880166705 0.0861337079 C 0.0745079 1 17 0.072898585 1 AJ 1.495191 x lo-’ 1.441514 x lo-’ AJK -1.477762 x -1.458105 x lo-’ A, 5.284089 x lo-’ 5.281053 x lo-’ 6, 3.649558 x lo-’ 3.519435 x lo-’ 4.461253 x lo-’ 4.789547 x lo-’ 8,number of transitions 817 556 standard deviation of fit 0.8304 0.9901 correlation matrices: ~ ~~ C ’C1 ,F, VO A-B B B-C AJ AJK A, VO 100 3 -47 2 -33 2 -3 A-B 3 100 -82 52 -41 16 30 B -47 -82 100 -63 45 -6 -25 B-C 2 52 -63 100 21 -35 40 AJ -33 -41 45 21 100 -86 59 AJK 2 16 -6 -35 -86 100 -85 AK -3 30 -25 40 59 -85 100 ~~ C3 7C1 ’Cl F, VO A-B B B-C AJ AJK AK 100 -15 -28 -14 -38 19 -25VO A-B -15 100 -85 70 -26 -2 49 B -28 -85 100 -72 40 -2 -34 B-C -14 70 -72 100 23 -46 61 AJ -38 -26 40 23 100 -88 59 AJK 19 -2 -2 -46 -88 100 -85 AK -25 49 -34 61 59 -85 100 Ref.44.The numbers in parentheses are one standard deviation according to the least-squares fit in units of the least significant figure quoted. Ground-state constants are constrained to those of ref. 32. Note B = +(I3 + C). Correlation matrices for the fits are presented below the table.Fitted parameters. ‘Constrained to the ground-state value. Plate 1 Loomis-Wood diagram of the spectrum of CCl,F, in the region 1154.1-1159.9 cm-’. The PP,, series of C35C1,F, is displayed vertically in the centre, the diagonal series immediately above corresponds to pP,ztransitions of C3’C13’C1F2. D. McNaughton et al. (Facing p. 1058) J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 stants are to be used to model band contours for temperature analysis. Calculated rotational constants have been used to simulate the spectrum as a check on the assignment and in order to measure to rotational temperature in our spectrum. Although centrifugal distortion was not included, the spectrum is none the less well reproduced, as illustrated by the plots in Fig.4(c) and Fig. 5. The few spectral features that are unaccounted for are probably due to the less abundant C37C12F2 isotopomer. The only anomalous values amongst the fitted parameters are the A rotational constants for the v8 state which are 0.0003 cm-’ greater than the ground-state values for both isotopic species. This apparent increase in A rather than the expected decrease associated with a stretching mode may result from an a-axis Coriolis interaction with a nearby vibrational level such as (v2 + v3) or possibly a &-dependent Fermi resonance with a vibrational level such as (v2 + vg). These energy levels are shown schematically in ref. 39. The band centres for C3’C1,F2 and C3’C13’C1F2, calculated at 1161.08498 (4) and 1160.96467 (6) cm-’,respectively, are consistent with the pre- viously reported Q branch positions of 1161.07 and 1160.95 cm -from the medium-resolution Q branch analysis.36 The rotational temperature in the ground vibrational state was estimated at 40 K by comparison of the observed and calculated spectra using Q branch widths and P and R branch profiles.Lower temperatures could have been achieved through seeding in argon, but this would have the undesirable effect of decreasing absorption strength, and a rotational temperature of 40 K proved cool enough to resolve most of the rotational structure at 0.0034 cm-’. Although the simulated spectrum, calculated on the basis of a Boltzmann distribution at 40 K, shows little deviation from the observed spectrum, the apparent population distribution in the ground vibrational state should not be Boltzmann-like for a number of reasons.First, a small amount of warmer background gas is present in the sample chamber. Secondly, the design of the external sample chamber with its parallel beam means that the interaction zone is broad and molecules will exhibit a range of temperatures since they are sampled at a range of distances and angles from the nozzle aperture. Thirdly, relaxation is not complete in a molecular beam, so that even if the jet was probed at a well defined distance from the nozzle, the distribution would not be Boltzmann-like. Collision-induced rotational relaxation has been found to follow the dipole selection rules AJ = 0, f.1, AK = 0 and + ++-for symmetric tops.4s As Snavely et al.pointed out,2 the AK = 0 rule tends to cause molecules to relax within the same K-stack, and because the AK # 0 transitions are slower, the lowest J levels of each K-stack would be expected to be populated significantly. This is consistent with the observed pattern. Transitions are observed for relatively high K, values (up to K, = 25 in the ground state), but only corresponding to the lowest J levels in each K,-stack. In order to determine the rovibrational constants of the v8 band more accurately, higher J and K transitions might be obtained from room- temperature spectra and combined with those of the present study. Supplementary tables of assigned transitions of CC12F2 are available from the authors or from the British Library.? Conclusion An apparatus for high-resolution FTIR-jet spectroscopy has been constructed involving a cryopump and a multiple-pass configuration for greater signal absorption.Reasonable t Supplementary publication no. SUP 57001 (22 pp.), deposited with the British Library. Details are available from the Editorial Office. signal-to-noise spectra were recorded for the v8 band of CC12F2 despite the weak P and R structure of this band rela- tive to v1 and v6, the other fundamentals in this spectral region. The v8 band has been assigned using a Loomis-Wood interactive fitting program to select out the regular structure that occurs at higher values of K,. Molecular constants have been obtained through weighted least-squares fits of the observed transitions and used successfully to simulate the v8 band profile.This demonstrates the usefulness of FTIR-jet spectroscopy for resolving complicated overlapping tran-sitions for moderately sized molecules. Significant vibrational population can be achieved in a supersonic jet by moderate heating of the nozzle without adversely affecting rotational cooling. The financial assistance of the Australian Research Council and the Sir James McNeill Foundation is gratefully acknow- ledged. References 1 A. Amrein, M. Quack and U. Schmitt, J. Phys. Chem., 1988, 92, 5455. 2 D. L. Snavely, S. D. Colson and K. B. Wiberg, J. Chem. Phys., 1981,74,6975. 3 D. L.Snavely, K. B. Wiberg and S. D. Colson, Chem. Phys. Lett., 1983,%, 319. 4 D. L. Snavely, V. A. Walters, S. D. Colson and K. B. Wiberg, Chem. Phys. Lett., 1984, 103,423. 5 V. A. Walters, D. L. Snavely, S. D. Colson, K. B. Wiberg and K. N. Wong, J. Phys. Chem., 1986,90,592. 6 H. R. Dubal, M. Quack and U. Schmitt, Chimia, 1984,38,438. 7 A. Amrein, M. Quack and U. Schmitt, Mol. Phys., 1987,60,237. 8 A. Amrein, M. Quack and U. Schmitt, Z. Phys. Chem., 1987,154, 59. 9 A. Amrein, H. Hollenstein, P. Locher, M. Quack and U. Schmitt, Chem. Phys. Lett., 1987, 139,82. 10 A. Amrein, D. Luckhaus, F. Merkt and M. Quack, Chem. Phys. Lett., 1988,152,275. 11 A. Amrein, H. Hollenstein, M. Quack and U. Schmitt, Injured Phys., 1989,29, 561. 12 A. J. Ross, A.Amrein, D. Luckhaus and M. Quack, Mol. Phys., 1989,66,1273. 13 H. Burger, A. Rahner, A. Amrein, H. Hollenstein and M. Quack, Chem. Phys. Lett., 1989,156,557. 14 M. Quack, Annu. Rev. Phys. Chem., 1990,41,839. 15 M. Snels and M. Quack, J. Phys. Chem., 1991,%, 6355. 16 M. Quack, U. Schmitt and M. A. Suhm, Chem. Phys. Lett., 1993, 208,446. 17 J. A. Barnes and T. E. Gough, Chem. Phys. Lett., 1986,130,297. 18 J. A. Barnes and T. E. Gough, J. Chem. Phys., 1987,86,6012. 19 A. D. Walters, M. Winnewisser, K. Lattner and B. Winnewisser, J. Mol. Spectrosc., 1991, 149, 542. 20 B. D. Rehfuss, M. H. Suh, T. A. Miller and V. E. Bondybey, J. Mol. Spectrosc., 1992, 151,437. 21 J. K. Holland, M. Carleer, R. Petrisse and M. Herman, Chem. Phys. Lett., 1992, 194, 175.22 F. Melen, M. Carleer and M.Herman, Chem. Phys. Lett., 1992, 199, 124. 23 F. Melen, M. Herman, G. Y. Matti and D. McNaughton, J. Mol. Spectrosc., 1993,160, 601. 24 J. Ballard, D. Newnham and M. Page, Chem. Phys. Lett., 1993, 208,295. 25 F. S. Rowland, Annu. Rev. Phys. Chem., 1991,42,731. 26 D. G. Cogan, Stones in a Glass House, Investor Responsibility Research Centre Inc., Washington, DC, 1988, p. 37. 27 M. Snels and W. L. Meerts, Appl. Phys. B, 1988, 45, 27, and references therein. 28 F. Y. KO,F. Tsai and E. L. Beeson Jr., Bull. Am Phys. SOC., Ser. II, 1968, 13,253. 29 C. F. Su and E. L. Beeson Jr., J. Chem. Phys., 1977,1,330. 30 H. Takeo and C. Matsumura, Bull. Chem. SOC., Jpn., 1977, 50, 636. 31 R. W. Davis and M.C. L. Gerry, J. Mol. Spectrosc., 1983, 101, 167. 1060 J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 32 R. A. Booker and F. C. De Lucia, J. Mol. Spectrosc., 1986, 118, 40 J. Orphal, B. Sumpf, K. Herrmann, V. V. Pustogov, F. Kuhne-548. mann, Proc. XII Int. Conf. High Res. Infiared and Mocrowave 33 S. Giorgianni, A. Gambi, L. Franco and S. Ghersetti, J. Mol. Spec., 1992, C19. Spectrosc., 1979, 75, 389. 41 P. Wallraff, K. M. T. Yamada and G. Winnewisser, J. Mol. 34 M. Morillon-Chapey, A. 0. Diallo and J-C. Deroche, J. Mol. Spectrosc., 1987, 126, 78. Spectrosc., 1981, 88,424. 42 D. McNaughton, D. McGilvery and F. Shanks, J. Mol. Spec-35 H. C. Jung, Bull. Korean Chem. Soc., 1988,9,275. trosc., 1991, 149, 458. 36 H. Jones and M. Morillon-Chapey, J. Mol. Spectrosc., 1982, 91, 43 D. McNaughton and E. G. Robertson, J. Mol. Spectrosc., 1994, 87. 163, 80. 37 H. Jones, G. Taubmann and M. Morillon-Chapey, J. Mol. Spec-44 J. K. G. Watson, in Vibrational Spectra and Structure, ed. J. R. trosc., 1985, 111, 179. Durig, Elsevier, Amsterdam, 1977, vol. 6, p. 1. 38 G. Taubmann and H. Jones, J. Mol. Spectrosc., 1986,117,283. 45 T. Oka, J. Chem. Phys., 1968,48,4919. 39 S. Giorgianni, A. Gambi, A. Baldacci, A. De Lorenzi and S. Ghersetti, J. Mol. Spectrosc., 1990, 144,230. Paper 3/07081F; Received 30th Nouernber, 1993

ISSN:0956-5000    

DOI:10.1039/FT9949001055

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. CHEM. SOC. FARADAY TRANS., 1994, 90(8), 1061-1063 Clusters of C,, Molecules David J. Wales University Chemical Laboratories, Lensfield Road, Cambridge, UK CB2 1EW Clusters of 13, 19 and 55 c60 molecules are investigated by molecular dynamics simulation and in terms of their potential-energy surfaces. For (c60)55 nearly 3000 rearrangement pathways have been calculated and compared with a similar sample for a 55-atom cluster bound by the simpler Lennard-Jones potential. Striking differences are revealed between these systems, both in terms of the potential-energy surface and thermodynamic proper- ties. These results are due to the shorter range of the c60 intermolecular potential :for example, the rearrange- ment mechanisms of (c60)55 are generally much more localised that those of LJ5, .Often it is possible to obtain insight into bulk behaviour by considering the corresponding properties of finite clusters,' for which detailed and systematic calculations may be pos- sible. Here we consider clusters of 13, 19 and 55 c60 mol-ecules in the light of recent work by Hagen et d.and Cheng et al. which suggests that the bulk liquid phase of c60 has only a narrow range of stability2 or none at all.3 The model intermolecular potential employed is that of Girifal~o,~ which has a significantly shorter effective range than the atomic Lennard-Jones potential that is often used to provide a qual- itative description of inert gases.3 In fact, Ashcroft has used a system of rigid spheres as the starting point for his discussion of the unusual c60 phase diagram.' Reducing the range of a pairwise potential increases the number of minima on a cluster potential-energy surface (PES), decreases the probabil- ity of the system being associated with the global minimum, and leads to larger rearrangement barriers, making glassy or amorphous structure more The molecular dynamics calculations provide starting points for a separate energy minimisation procedure to locate a representative sample of local minima on the PES.High- energy trajectories were employed with average temperatures of between 400 and 500 K. At these energies it was necessary to place the clusters in a container to prevent evaporation; the evaporation rate would also be a useful diagnostic in the present context, but was not considered further in this study.A cluster PES may be viewed as a mountain range whose peaks and wells represent energy maxima and minima, respectively. Minimum-energy rearrangement pathways between two different minima are valley bottoms, and the transition state is the saddle point, or pass, between such valleys. Minima, transition states and rearrangement mecha- nisms in the present work were all calculated by eigenvector- followingg using an implementation that has been described before and applied to numerous cluster systems.lo This method enables transition states to be located by systemati- cally maximising the energy for one particular degree of freedom and simultaneously minimising in all the other direc- tions.Minima are located within the same framework by minimising for all degrees of freedom.? Analytic first and second derivatives of the energy were employed at every step, and the resulting energies and geometries are essentially exact for the model potential in question. In total 138, 1132 and 1947 different local minima were located for (c60)13, (c60)19 and (c60),,, respectively. The t Strictly speaking the pathways located by this method, namely minimising the energy using eigenvector-following after suitable dis-placements from the transition states, are not equivalent to minimum-energy pathways. However, they should be close enough for the present purposes. number of distinct minima actually increases much faster with the number of molecules than these numbers suggest; we assume that a representative sample has been obtained in each case.' For these sizes Lennard-Jones clusters (hereafter denoted LJ,) each exhibit a particularly stable, high-symmetry minimum.For 13 and 55 these are Mackay icosahedra12 with 1, point group symmetry (see Plate 1); for 19 the low-energy minimum is a D5, decahedron. The special stability of such high-symmetry structures for the Lennard- Jones potential, conferred by the completion of geometrical packing sequences, leads them to be known as 'magic numbers '. For (c60)13 and (c6O)lg only a few transition states and rearrangement pathways were calculated, with particular emphasis on the lowest-energy structures.For (c60)55 a sys- tematic survey was conducted, as results for this system are more likely to provide insight into bulk behaviour, and 2945 different transition states were located, all having C, sym- metry. A dataset of 3481 transition states has been analysed previously for LJ,, ,and all the corresponding rearrangement pathways have been characterised for both systems. Here we consider some of the key results. A selection of minima and transition states is given in Table 1. For (c60)13the icosahedron is the lowest-energy minimum found by quenching, and is probably the global minimum. However, there are two C, and C,minima which also have low energies. The former structure is linked to the 1, minimum by a facile rearrangement, and the C, minimum is linked to the C, by a mechanism that is almost barrierless.For LJ13 the 1, geometry has a uniquely low energy and must overcome large barriers in order to rearrange.13 The 0, cuboctahedron is a transition state for a degenerate rearrangement of the icosahedron, as it is for LJ,,. The D5, bicapped pentagonal prism is also a transition state, but mediates a degenerate rearrangement for a C, minimum in (c60)13 as opposed to the icosahedron in LJ13. The differ- ences are more pronounced between LJ19 and (c60),9, where the D,, global minimum of the former system corresponds to a saddle point of index 8 for (c60)19, i.e. it has eight normal modes with imaginary frequencies. Most low-energy minima and transition states of (c60)19have no symmetry elements at all.For (c60)55 both the cuboctahedron and icosahedron are minima and the former lies lower in energy. The two are linked by a transition state of Th symmetry (Plate 1) in a mechanism which is the realisation of a hypothetical process recognised by Mackay.' 2,14 The analogous mechanism has been found for LJ147 in an ongoing study of the rearrange- ments of model clusters with high symmetry. For LJ,,, the cuboctahedron is a transition state for a degenerate rearrangement of the icosahedron,' ' and cuboctahedral 1062 N energy 13 -38.19416413 13 -38.141 68081 13 -38.140 850 19 13 -38.140 842 04 13 -38.110192 58 13 -37.954 827 57 13 -37.944 162 11 13 -37.827 224 60 13 -37.175 586 27 19 -61.704 878 44 19 -61.703011 64 19 -59.1 88 687 96 55 -229.625 137 32 55 -229.491 394 04 55 -227.339 730 86 55 -223.873 227 74 55 -223.798 559 01 55 -223.791 83431 55 -219.767035 14 55 -218.484972 37 147 -700.581 584 72 147 -681.692 751 54 147 -667.527 597 90 J.CHEM. SOC. FARADAY TRANS., 1994,VOL. 90 index PG comments 0 0 'h c2 global minimum, Mackay icosahedron second lowest minimum 0 cs third lowest minimum 1 1 0 1 1 1 0 0 Cl c2 c5 c5 D5h Oh c2 cs links C2 and C, minima, w = 4.2ian-' links C2 and I, minima, w = 4.6ian-' links C, minimum to I,, w = 2.lian-' degenerate rearrangement of C, minimum, w = 1.6i cm-' degenerate rearrangement of minimum, w = 2.6i cm-' lowest minimum found for (c6,)19second lowest minimum 8 0 0 0 D5h Cl C, Oh decahedron analogous to global minimum for LJ,, lowest minimum found for (C60),, second lowest minimum found for (C,,),, cuboctahedron 0 0 'h c3v Mackay icosahedron C3, minimum 1 1 7 c3v Th D5h decahedron links C3, and I, minima, w = 3.3i cm-' mediates 0,to I, rearrangement, w = 2.9icm-' 0 Oh cuboctahedron 0 1 'h Th Mackay icosahedron mediates 0,to I,, rearrangement, w = 2.9icm-' The unit of energy is the pair well depth (3218.43K), N is the number of molecules in the cluster, the index is the number of imaginary normal-mode frequencies (0 for a minimum, 1 for a transition state), and PG is the point group. The unique imaginary frequency, w, is also given for the transition states. Lennard-Jones clusters do not become lower in energy than Mackay icosahedra of the same size until they are much larger.16 For LJ,, there is a D,, minimum,', while for (c60),,the corresponding structure is a saddle of index 7. However, there is a true C, minimum linked to the icosahe- dron uia a C, transition state.Neither the Oh nor the 1, minimum is found among the sample of 1947 minima obtained by quenching; two of the latter set belong to point group C,, and the rest are C,. Many significantly lower- energy minima exist for this cluster, and it is quite possible that the global minimum has not yet been located; the precise identity of the latter structure is probably unimpor- tant. These lower-energy disordered clusters also have larger mean vibrational frequencies than the 0,and 1, geometries.In previous studies where large numbers of minima have been located for model clusters, the most similar behaviour to (c60),, occurs for (H20)20, a 'frustrated' system." For LJ,, , in contrast to (c60),,and (H20)20, the global minimum is still located in quenches even at energies where the system is highly non-rigid. The tendency of c60 clusters to appear glassy or amorphous is fundamentally related to the form of the intermolecular potential. The latter governs the packing characteristics and the intolerance of strains which result for icosahedral geometries. The short-range potential means that local packing considerations are more important than the global correlations which would produce high-symmetry structures.These differences are also reflected in the distribu- tions of local minima with energy, where for LJ,, the low- energy range is dominated by structures based upon icosahedral order. More striking differences between the LJ,, and (c60)55 pathways are revealed in other properties. For example, Fig. l(a) and (b) show the normalised probability distributions for the smaller and larger barrier heights calcu- lated for all the rearrangement mechanisms. Clearly the (C60)5,cluster must generally overcome significantly greater barriers (relative to the pair well depth) in order to explore new regions of the PES. Fig. l(c) shows the probability dis- tributions for the cooperativity index,18 y, which is a measure of how many atoms are involved in a given rearrangement.Both LJ,, and (c&, show a peak for localised processes around y = 50, but the large peak for small y corresponding to cooperative mechanisms is entirely absent for (C,,),, . The short range of the potential for the latter cluster destroys the global correlations found for LJ,, . To relate the present results to the question of the bulk liquid stability we must consider two questions. First, how is the relatively unfavourable nature of the bulk liquid mani- fested in a microcanonical cluster simulation? Secondly, how are these characteristics of the cluster determined by the PES? As Hagen et al. point there will be no bulk liquid phase if the solidbiquid coexistence line lies above the liquid/ vapour critical point in temperature.This will occur if solid/ liquid coexistence is shifted to unusually high temperature, if liquid/vapour coexistence is shifted to unusually low tem- perature, or a combination of both factors. In the cluster simulation the presence of a container discriminates against the gas phase because it restricts the accessible volume. However, we should certainly be able to comment upon solidbiquid coexistence. A particular property of small systems is that the melting transition occurs over a finite range of temperature (or energy) for which solid- and liquid- like forms of the cluster coexist, and this leads to features in the microcanonical caloric curve, T(E),and the probability distribution of the short time averaged temperat~re.'*'~ The (c&, PES exhibits a complex glassy or amorphous struc- ture, with deep wells and high barriers (relative to the pair well depth).t The same is likely to be true in the bulk, and one might therefore argue that the solidbiquid coexistence region shifts to higher energy in the microcanonical ensemble because of the reduced entropy difference between the solid and liquid states.The present simulations of (c6& suggest t The nature of the surface may make ergodicity dificult to achieve in both cluster and bulk simulations. The true global minimum for (C&s with this potential is also unknown; the effect of starting molecular dynamics simulations from a higher-energy minimum would be to decrease the temperature for low-energy tra- jectories.5 .r(3 I 5 M rd Aa.r( v c eB9Y 0P2 (d 0 Y J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 1.6 1.2 0.8 0.4 0.0 012345 energy/pair well depth ?! 0.5-,/!, 0246810 energy/pair well depth 0 10 20 30 40 50 60 Y Fig. 1 Comparison of normalised probability distributions (obtained by binning and smoothing) between (C,,),, (-) and LJ,, (---). (a) Smaller and (b)larger barrier height sampled over all the different rearrangement mechanisms. The unit of energy for the horizontal axis is the appropriate pair well depth for both clusters. (c) Distribution for the dimensionless cooperativity index, y. The peaks around 50 are for relatively localised rearrangements where only a few atoms move significantly; the peak around 5 [absent for (c6o)ss] is for relatively delocalised processes, where most of the atoms in the cluster are involved.that the melting process is gradual (Fig. 2), as expected for a disordered solid,* and non-rigidity (as judged by the Linde- mann 6) sets in more slowly than for LJ,,, reaching essen- tially the same asymptotic value at higher total energy. The present results are also relevant to the formation of soot, in particular in the high-temperature synthesis of C6,. Deposition from the vapour must initially involve small clus- ters, and hence we would expect such soots to be amorphous. Note that the ‘magic numbers’ found by Martin et al.” for positively charged C,, clusters are actually similar to those found for Lennard-Jones clusters.Here the presence of the charge must modify the intermolecular potential significantly, introducing longer-range ordering and the recovery of special 0.34-1 I I 1 -7---40 50 60 70 80 energy relative to lowest minimum/pair well depth Fig. 2 Caloric curves for (C,,),, (---) and LJ,, (. *. * .) from molec- ular dynamics simulations. The temperature (reduced units) is calcu- lated by equipartition and the total energy is relative to the lowest known minimum. Each trajectory consisted of 2.5 x 10, time steps equivalent to about 25 ns for (C,,),, ; the error bars are one stan- dard deviation in height. Both curves were obtained by progressively raising the energy from the lowest minimum, with lo5 equilibration steps between production runs.Note the well defined S bend for LJSS . stability for structures with favourable geometrical packing arrangements. The author is a Royal Society Research Fellow. References 1 R. S. Berry, J. Chem. SOC.,Faraday Trans., 1990,84,2343. 2 A. Cheng, M.L. Klein and C.Caccamo, Phys. Rev. Lett., 1993, 71, 1200. 3 M. H. J. Hagen, E. J. Meijer, G. C. A. M. Mooij, D. Frenkel and H. N. W. Lekkerkerker, Nature (London), 1993,365,425. 4 L.A. Girifalco, J. Phys. Chem., 1992,%, 858. 5 N. W. Ashcroft, Nature (London), 1993,365,387. 6 P. A. Braier, R. S. Berry and D. J. Wales, J. Chem. Phys., 1990, 93,8145. 7 F. H. Stillinger and D.K. Stillinger, J. Chem. Phys., 1990,93, 6106. 8 J. Rose and R. S. Berry,J. Chem. Phys., 1993,98,3262. 9 J. Pancik, Collect. Czech. Chem. Commun., 1974,40,1112;C. J. Cerjan and W. H. Miller, J. Chem. Phys., 198 1,75,2800. 10 D. J. Wales, Mol. Phys., 1991, 74, 1; J. Chem. SOC., Faraday Trans., 1992,86,3505; 653; 1993,89,1305. 11 D. J. Wales, Mol. Phys., 1993,78, 151. 12 A. L. Mackay, Acta Crystallogr., 1962,15,916. 13 D. J. Wales and R. S. Berry, J. Chem. Phys., 1990,92,4283. 14 J. Farges, M.F. Feraudy, B. Raoult and G. Torchet, Acta. Crys- tallogr., Sect. A, 1982, 38,656. 15 J. Uppenbrink and D.J. Wales, J. Chem. SOC., Faraday Trans., 1991,87, 215. 16 R. W. Hasse, Phys. Lett. A, 1991,161, 130;B. Raoult, J. Farges, M. F. De Feraudy and G. Torchet, Philos. Mag. B, 1989,60, 881;J. A. Northby, J. Xie, D. L. Freeman and J. D. Doll, Z. Phys. D,1989,12,69. 17 D.J. Wales and I. Ohmine, J. Chem. Phys., 1993,98,7245. 18 F. H.Stillinger and T. A. Weber, Phys. Rev. A, 1983,28,2408. 19 D. J. Wales and R. S. Berry, Phys. Rev. Lett., submitted. 20 T. P. Martin, U. Naher, H. Schaber and U. Zimmerman, Phys. Rev. Lett., 1993,70, 3079. Paper 4/00718F; Received 8th February, 1994

ISSN:0956-5000    

DOI:10.1039/FT9949001061

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. CHEM. SOC. FARADAY TRANS., 1994, 90(8), 1065-1072 Fourier-transform Luminescence Spectroscopy of Solvated Singlet Oxygen Alisdair N. Macpherson and T. George Truscott" Department of Chemistry, Keele University, Keele , Staffordshire, UK ST5 5BG Paul H. Turner Applications and Support Group, Bruker Spectrospin Ltd., Banner Lane, Coventry, UK CV4 The emission peaks and solvent-induced spectral shifts of the singlet oxygen transitions to the ground and first vibrational level of the ground triplet state of oxygen have been determined in a large number of solvents. The spectra were measured with a substantially higher accuracy than previously reported, by use of an FT spec-trometer and a filtered white-light source. The results were interpreted in terms of the formation of van der Waals (vdW) complexes of singlet oxygen with four or six solvent molecules and existing theory satisfactorily accounts for the observed shifts in a number of solvents.For perfluorocarbons, no vdW complex is formed and it is suggested that weak long-range repulsive forces dominate, leading to small blue shifts in the emission peaks. The theory as used takes no account of specific interactions such as charge transfer, which could explain why the shifts predicted for the dispersion forces are smaller than the observed shifts in solvents of low ionisation potential. In solvents such as benzene, pyridine, toluene, hexachlorobutadiene, tetrachloroethene and iodopentafluorobenzene, charge-transfer inter- actions between all the solvent molecules and singlet oxygen are apparently important and lead to a further stabilisation of the complex.The bandwidths of the transitions did not correlate particularly well with the radiative rates, but did show a good correlation with the solvent spectral shifts. A number of other subtle solvent perturbations were observed. The ratio of the intensities of the (0-0)to (0-1) transitions showed a solvent dependence, as did the vibrational spacing of the ground triplet state of oxygen. These results indicate the existence of weak ground-state complex- es and a relaxation of the poential-energy surfaces describing the complex states. The photophysical properties of singlet molecular oxygen [02('Ag)] in the gaseous and condensed phases have been the subject of many experimental studies in the past decade.' Since near-infrared detectors sensitive to the emission from singlet oxygen at 1270 nm became commercially available, this direct detection technique has been widely used to inves- tigate the formation and decay of singlet oxygen.However, as the 02('Ag) -+ 02(3Zg-) transition is highly forbidden and non-radiative deactivation processes dominate in solution, detectors with high sensitivity are required. It is known that the lifetime of singlet oxygen is highly dependent on the molecular structure of the solvent, varying from 3.09 ps in water2 to ca. 77 ms in air-saturated trichloro-fluor~methane.~.~This quenching of singlet oxygen by solvent molecules has been interpreted as a collisional electronic-to-vibrational energy transfer to the oscillators X-Y of the solvent molecule with the highest fundamental vibrational energy [process (l)], where E, is the off-resonance energy In weakly deactivating solvents, those which have only the low vibrational energy oscillators C-F or C--1, singlet oxygen is quenched predominantly by ground-state oxygen [process (211. 02(1Ag)u,=o+ X-Y,.,=, -+ 02(3Zg-)u,+,, + x-Yut.=, + E, (1) 02('A3,.=0 + 02(3Z;)u,,=0-+ 02(3Zg-)u,,=m02(3~,)u~f=5-m4-Em (2) The solvent dependence of the radiative rate has also been e~tablished,4.~*'~-'~and relative to benzene (k, = 1.5 s-')~ the radiative rate varies from 0.14 s-' in trifluoroethanol to 3.5 s-l in carbon disulfide,' or from 0.18 s-' in water to 3.0 s-in 1-meth~lnaphthalene.~ These solvent-dependent radi- ative rates are substantially larger than in the gas phase and show an approximate correlation with the solvent polarisabil- it^.^ It is clear then, that the solvent not only induces the 02(lAg)-+ OJ~Z;) transition in the collision complex, but also accepts the electronic energy of 02('Ag).In a spectral study of solvated singlet oxygen, however, the phosphor- escence peak positions of both the (0-0) and (0-1) transitions were reported to be independent of the solvent, although new emissions bands assigned to simultaneous electronic-vibrational transitions involving both 02('Ag) and a vibra- tionally excited solvent molecule [m= 0 and s = 1 in process (l)], were 0b~erved.I~ The singlet oxygen peak positions were then assumed to be unshifted from the gas-phase values of 1268.6 and 1580.8 nm, for the 02(1Ag)u,=0+02(3Z;)u,,=0and O,('A,),.=o 02(3Z;)utt= transitions." More recently, small solvent-induced shifts in the emission peaks were reported and although there was no clear correlation with solvent polarisability, the largest shifts were observed in the solvents with the highest refractive indices.' 6*17Small shifts (<7 nm from the 1265 nm peak in the gas phase)," have also been seen in the absorption spectra of singlet oxygen mea- sured at high oxygen pressures in a number of Determination of such small, solvent-induced changes in the peak positions of extremely weak emission bands is difi- cult with conventional dispersive spectrometers.However, the use of a Fourier-transform spectrometer offers a number of important advantages" for the precise detection of the singlet oxygen peak positions and these have been demon- strated in the gas phase.20 By using an interferometer to resolve the emission, the optical throughput is increased and an improvement in the sensitivity is obtained, as the slits are replaced by circular apertures (Jacquinot's advantage). Sec- ondly, as the entire spectral region is simultaneously observed by the detector, the noise is distributed throughout the transformed spectrum, resulting in an increase in the signal-to-noise ratio, if the noise is random and independent of the signal intensity (Fellgett's multiplex advantage). Other advantages are the very high precision of the wavenumber axis (Connes advantage), as an internal He-Ne reference laser is used for calibration, and the rapid signal acquisition times (in our experiments 1 scan s-', at 16 cm-' resolution).We have used these advantages of FT spectroscopy to record the emission from solvated singlet oxygen with a high accuracy and we have then correlated the shifts with the physical properties of the solvent. In this paper we report the peak positions and spectral bandwidths in a number of different solvents and show that most of the spectral shift observed can be accounted for by consideration of the weak dispersion interactions between at least four solvent molecules and singlet oxygen in a van der Waals complex.Experimental Materials The solvents used were carbon disulfide (CS, , 99+ %), dichloromethane (CH,Cl, , 99+ %), chloroform (CHCl, , 99.8%), [2H]-trifluoroacetic acid (CF,CO,D, 99 atom% D), tetrachloroethene (C,Cl,, 99+ %), 1,1,2-trichloro-trifluoroethane (C,F,Cl, , 99+ %), 1,Zdibromotetrafluoro-ethane (C,F,Br, , 99.5+ %), hexachlorobut-1,3-diene (C,C16, 98%), ['H,]pyridine (C6D5N, 99 atom% D), hexa-fluorobenzene (C6F6, 99%), chloropentafluorobenzene (C,F, Cl, 99%), bromopentafluoro benzene (C6F5Br, 99%), iodopentafluorobenzene (C6F,I, 99%), perfluorohexane (C6F1,, 99Yo)and toluene (C6H,CH3, 99+ %) from Aldrich. [2H4]Methanol (CD,OD, 99.8 atom% D), [2H,]dichloromethane (CD,Cl, , 99.8 atom% D), [2H]chloroform (CDCl, ,99.8 atom% D),[2H,]acetonitrile (CD,CN, 99.8 atom% D), C2H6]acetone (C,D6C0, 99.8 atom% D), C2H,]benzene (C6D6, 99.6 atom% D) and ['H,]toluene (C6D,CD3, 99 atom% D) were obtained from GOSS Scientific Instruments Ltd.Trichlorofluoromethane (CCl,F, >99.5%) and dibromodifluoromethane (CF,Br, , >98%) were from Fluka, carbon tetrachloride (CCl, , 99+ YO)was from Janssen Chimica and perfluorodecalin isomers (CIoF14), perfluoroperhydrophenanthrene (C14F24) and perfluoro(bicyclo[4.4.O]decyl)cyclohexylmethane (C,7F30, perfluoroperhydrobenzyltetralin)were a gift from D.S.L. Slinn of RhGne Poulenc Chemicals (ISC Division, Bristol UK). All solvents were used as received, except C,F,Cl,, which was redistilled over 4B molecular sieves.The sensitisers used were 5,10,15,20-tetra(4-sulfonato)phenylporp-hine (TPPS, Porphyrin Products) in methanol and tri-fluoroacetic acid, 5,10,15,20-tetrakis(pentafluorophenyl) porphine (TPPF, Aldrich) in the perfluorocarbons and 5,10, 15,20-tetraphenylporphine(TPP,99+ %, Aldrich) in all other solvents. All solutions were air-saturated and the experimen- tal temperature was 22"C. FT Luminescence Measurements The experimental details have been described elsewhere,t but briefly, the near-infrared emission was recorded using a Cali- brated FT-Raman spectrometer (Bruker FRA 106 FT-Raman module adapted to a IFS 66 FTIR bench). Singlet oxygen was generated by irradiating solutions of a sensitiser in micro-cells with ca.4 mW cm-,of 405 nm light from a fil-tered tungsten lamp. The emission was filtered with a 1050 nm long-pass silicon filter and the modulated emission from the interferometer was detected with a liquid-nitrogen-cooled germanium photodiode (noise equivalent power, NEP < lo-', W Hz-",). The luminescence spectra were ~ ~~~ t Appl. Spectrosc. in the press. J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 corrected with the instrumental response curve for the FT spectrometer. Results Effect of Solvent on the Peak Positions The shift in the emission peaks and also the increase in the bandwidths (from 68 to 122 cm-') in several solvents, all recorded with a resolution of 8 cm-',are apparent in Fig. l(a) for the (0-0)band and Fig.l(b) for the (0-1) band. The emission peak maxima and the bandwidths are listed for all the solvents we studied in Table 1, along with the ratio of the intensities of the (0-0)to (0-1) transitions. We failed to resolve any emission from singlet oxygen in D,O and C,D6S0, when using the same excitation conditions, presum- ably because of the low phosphorescence yields in these sol- vents. Some of our results can be compared with recent measure- ments of the (0-0)emission peak positions in a number of solvents.'6*' In these studies, small spectral shifts between solvents (<6 nm) were reported for the first time. One of the largest red shifts (8.4nm, 52 an-'), from the gas-phase peak position, was observed in carbon di~ulfide,'~ in excellent agreement with the result we obtained by FT spectroscopy.However, in other solvents the reported peak positions are different from the results we obtained by up to f17 ~m-','~9'~ which made the finding of correlations between the solvent spectral shifts and the physical properties of the solvent difficult. An approximate correlation of the observed solvent spectral shift (Avo,,*) with the refractive index of the solvent n was, however, noted16*17 and this is shown for our data as a plot of Avo& against the solvent polarisability (n2-l)/(n2 + 2) in Fig. 2. Although the points are rather scattered from the best-fit line, it is clear that the largest shifts are observed in the solvents with the highest polarisability. The specific advantages of FT spectroscopy also enabled us to record the (0-1) transition at a resolution of 8 cm-' in most of the perhalogenated solvents we studied.Since the wavenumber/cm-' rc.-UJca U .-C 6800 6600 6400 6200 6000 wavenurnber/cm-' Fig. 1 Effect of solvent on the peak positions and bandwidths of (a) the (0-0) singlet oxygen transition (solvents from left to right: CloF18, C6Fl4, C2F3C13, C6F5Br, eel,, C6D6and cs2)and (b)the (0-1) transition (solvents: C10F18, C,F,Cl,, C&,Br, CCI, and CS,) J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Table 1 Singlet oxygen spectral data (0-0)transition (0-1) transition ' ' sqvent v,,,/cm - 4121m- v,,Jcm - A1,2lm - 40-0,1~(0-1) yo-0 -vo-'/cm-' 7827.3 121.6 6285.1 117 94 1542 7850 107 7845.0 113.8 6293" 110 1552 7837 125 7846.8 107.3 6301 119 104 1546 7843.8 110.5 7849.2 1-02.8 6300.6 112 108 1549 7859.4 99.5 7857.7 99.5 7848.4 124.1 7870.8 90 7846.9 93 7865.4 92.5 6316.1 96.8 98 1549 7863.5 94.5 6310.1 91 106 1553 7849.0 114 7844.2 92.5 6294" 97 104 1550 7831.6 117 7838.4 117.5 6283" 146 90 1555 7867.4 82.5 63 16.8 87.8 98 1551 7862.6 95.0 63 13.8 85 98 1549 7859.1 88.3 6309.3 92.8 97 1550 7852.7 96.3 788 1.5 74.0 6326.5 84 115 1555 7838.8 114.5 7832.7 107 7882.2 68.0 6329.1 69.1 106 1553 788 1.8 63.5 6328.4 64.8 103 1553 788 1.9 63.0 6328.5 61 114 1553 7882.4 6326.0 1556 Nearly all emission bands were recorded at a resolution of 8 cm-'and usually 200 scans were co-added." Recorded at a 16 cm-' resolution. The accuracy of the peak positions is estimated to be & 1 or k3 cm-'at a resolution of 8 or 16 cm-'. The errors in the bandwidths are +5 and +15 cm-' at resolutions of 8 and 16 an-'; in the vibrational spacing the error is f3 cm-' and in the ratio of the intensities the error is f 15%. first observations of the (0-1) transition in solution at 1580 emission from singlet oxygen was detected. Using the emis- nmz' or at 1588 nm,22 shortly after the observation of the sion peaks listed in Table 1, the Stokes shifts were calculated (0-0) band in solution,23 there have been very few reports of and found to be rather scattered, 23 cm-' in the gas phase, this band, because of its extremely low intensity in most sol-14 cm-' in C2F3CI, ,18 ca.25 cm-' in CCl, and CHCl,, ca. vents. Recently, (0-1) bands were recorded in CCl, and CS, 34 cm-' in CS, and CD,OD and CQ. 46 cm-' in C6H6 and at a resolution of 9 nm (ca. 36 cm-') and a 5 nm (20 cm-') C,HSCH3." The Stokes shifts determined show no corre- difference was observed between the peak positions in these lation with the solvent-dependent terms (the relative permit- two solvents.'' The solvent spectral shifts determined for the tivities and refractive indices of the solvent) of the Lippert (0-1) transition are also plottkd in Fig. 2 and again a reason-equation.', able correlation of AvObs with the solvent polarisability is observed.Effect of Solvent on Bandwidths The absorption spectra measured at high oxygen pressures have been reportedll,18 for of the solvents from which In early spectral studies, relatively narrow and intense (0-0) bands were reported for C6F14 and CCl,, but broad and very weak bands were observed in H,O." A broadening of 60 r 1 the singlet oxygen emission bands was also observed as the concentration of sensitiser increasedz5 and although this50 c effect was not specifically studied, we did not observe any 40 -significant changes in the emission spectra from different solutions of a sensitiser in the same solvent. Many of the c I E 30. published spectra of singlet oxygen have large bandwidths, as 0'=-they were recorded with fairly large slitwidths, to improve the -20 throughput to the detector.As only small decreases in the Y bandwidth were observed when the resolution was increased g 10-from 8 to 2 cm-',a resolution of 1-2 nm (at 1270 nm) is sufficient to record the true bandwidth of the singlet oxygen emission. -101 ' I A strong solvent dependence on the bandwidths was also 0.15 0.2 0.25 0.3 0.35 0.4 found in this study (see Fig. 1) and the smallest bandwidths (n2-1)/(n2+ 2) were observed in the perfluorocarbons (63 cm-' for CI7F3J Fig. 2 Plot of the solvent polarizability against the observed spec- and the largest in CS, and CD3CN (124 cm-'). Our results tral shift (from the gas-phase value): (@) (0-0)peak shift; (0)(0-1) are in good agreement with previously reported bandwidths, peak shift.Numbers refer to solvents, see Table 1. recorded at a sufficiently high resolution, in both emissi~n~*'~.~~and absorption studies.12*18 An asymmetric (0-0) band with a similar bandwidth (10 nm) to the emission band recorded in C14F24 has been reported in liquid CFCl, at -100 "C, using a monochromator with a resolution of 1.2 nm (7.4cm-1).8 At room temperature the bandwidth was larger by a factor of 1.6, a consequence of the thermal energy of the solvent molecules. In the gas phase, the emission spectra show partially resolved rotational branches, when the resolution is t4 cm-', and the R branch (at higher energy) is observed to be more intense than the P branch.20*26Hence, it is reasonable to assume that the asymmetry observed in the solution phase is an indication of the underlying rotational structure.8 The (0-0) emission peak from C14F24, recorded at a resolution of 2 cm- ',was simulated (using a least-squares spectrum simulation routine) by superposition of three bands, representing the P, Q and R rotational branches.The agree- ment between the simulated and observed (0-0) emission peak, shown in Fig. 3(a),is very good, although some devi- ation is observed in the wing regions. The simulated three- band fit indicates that the emission band recorded in C14F24 I I I I I I I I I I 8300 8200 8100 8000 7900 7800 7700 7600 7500 7400 wavenumber/cm-Ir--l I II I I I I 8300 8200 8100 8000 7900 7800 7700 7600 7500 7400 wavenumber/cm-I I I I I I I I I 1 8300 8200 8100 8000 7900 7800 7700 7600 7500 7400 wavenumber/cm-l Fig.3 Simulation of the singlet oxygen bandwidths in (a) C14F24, (b) C6D6 and (c) CS, .The lowest curves show the observed spectra minus the calculated spectra. J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 is, in fact, fairly symmetric with almost equal contributions from the 'P'and 'R'bands. The spectral spacing between the simulated peaks appears to be fairly similar to the observed spacing between the Q and R branches in the gas phase.20.26 The singlet oxygen emission bands in solvents which show a large shift in the peak position and a larger bandwidth do, however, appear asymmetric. Three band simulations of the (0-0) emission peak (recorded at a resolution of 8 cm-') from C6D6 and CS, were also made and the results are shown in Fig. 3(b)and (c).The three band simulations in these solvents are shown to highlight the asymmetric nature .of the band and do not represent structure. There does not appear to be any specific correlation of the FWHM bandwidths (All2) with the singlet oxygen lifetimes in pure solvent. The singlet oxygen lifetimes in the solutions we used will be shortened as a result of quenching by the sensiti- ser and were not determined. There was, however, little differ- ence between the bandwidths in the few deuteriated and protonated solvents that we studied, even though there is at least a 20-fold difference in the singlet oxygen lifetimes.6 There is, however, a much better correlation of the FWHM bandwidth with the solvent polarisability (and hence the observed shift) and this is shown in Fig.4 as a plot of AvObs against Al12. As there is a correlation of both the radiative rates and the bandwidths with the solvent polarisability, we also expected there to be a correlation between k, and AIl2. With the perhalogenated solvents and carbon disulfide if an average value of k, =2.2 s-l is u~ed,~.~* an approximate correlation is observed, although in other solvents such as acetone, acetonitrile and methanol, there are large deviations. Effect of Solvent on the Relative Intensity Ratios and Interpeak Spacings Correcting the singlet oxygen luminescence spectra with the instrumental response function had only a minimal effect on the peak maxima and the bandwidths.It did, however, have a large effect on the ratio of the intensities of the (0-0) to (0-1) transitions, listed in Table 1. The ratios of the corrected peak intensities are slightly solvent dependent, varying from 11 5 in perfluorohexane to 94 in carbon disulfide, and these ratios are much larger than those previously reported in the solu- tion phase: 42 :1,2160 :1 (corrected)22 and 30 to 40 :l.17 The uncorrected spectra had (0-0) :(0-1) intensity ratios in the region of 60 :1. The gradients of the best-fit lines in Fig. 2 suggest that there is a smaller (by ca. 10 cm-') solvent spectral shift for the (0-1) band.However, this average solvent-induced decrease in the vibrational spacing of the ground state just reflects the scatter in the plot and the actual interpeak .1 50 - 015 I 4 014 4 r 30- 9 g 20-v) ,711 2 Y8 10-0 -10 i 60 70 80 90 100 110 120 130 bandwidth/cm-Fig. 4 Plot of the bandwidth against the observed solvent spectral shift. Numbers refer to solvents, see Table 1. J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 separations -v~-~),listed in Table 1, are also appar- ently solvent dependent. The vibrational spacing (Y" = 1 -Y" = 0) of solvated 02(3Zg-) is approximately unchanged in the perfluorocarbons from the gas-phase value of 1556 cm-', but is smaller by up to 11 cm-' in CS,. Although these differences are very small, the solvent inter- action follows the same general trends as those observed in the shift of the peak positions and additionally, we believe the spectra obtained by the FT spectroscopy technique are of suf- ficiently high quality and positional accuracy.Discussion Solvent Spectral Shits Although a general correlation between the radiative rate and the solvent polarisability has been found,7 a similar relation- ship with the solvent spectral shift was not previously observed, owing to the difficulty of measuring rather small shifts in extremely weak transition^.'^^'^ By using an FT spectrometer to resolve the emission from 'solvated ' singlet oxygen, we have determined not only the relative peak shifts in different solvents, but also the absolute peak positions with a higher precision.The emission maxima of the (0-0)bands in the perfluorocarbons are very close to the gas-phase value. The (0-1) bands, however, are blue shifted and although these shifts are small and within the estimated error range, they may be real. Small blue shifts have been observed in the absorption maxima of a weak benzene transition in per- fluorohexane at high pressures27 and also in helium.28 These small blue shifts, attributed to very weak long-range repulsive interactions, may be general to all solvents, but they are usually masked by the much larger red shifts due to disper- sion interactions between the solute and solvent molecules.28 The advantages of using perfluoroalkane solvents in spec- tral investigations have recently been reviewed and a number of their important properties were highlighted.27 These include exceptionally weak interactions with solutes (as the large vdW radius of F prevents the approach of oxygen to C atoms), very high oxygen solubilities (a consequence of the large free cavities in perfluorocarbons), typically three to ten times the equivalent hydrocarbon values and high photo- stability.These unique properties of perfluoroalkanes suggest that they are particularly good solvents in which to study the photoproperties of singlet oxygen. The lifetime of singlet oxygen is extremely long in perfluorocarbons and is limited only by intermolecular quenching by ground-state oxygen.' For solutes without a permanent dipole moment, a general red shift in the peak position of a transition from the gas phase is predicted, and is commonly observed, in the absence of specific interactions such as hydrogen bonding and charge transfer.The stabilisation of a more polarisable excited state, relative to the ground state, will increase as the refractive index and hence polarisability of the solvent increases. A linear dependence of the solent spectral shift on the Bayliss parameter 30 is often observed, where the constant K includes the oscil- lator strength of the transition. Taking the oscillator strength of the transition 02('Ag) t0,(3Zg-) to be f= 3.2 x the solvent spectral shift was calculated to be Q0.005 cm-l 16.It is known that the Bayliss equation often does not predict the correct order of magnitude of the solvent shift if the transition is weak, but a correlation between the polarisa- tion term and the observed shift may still be found.27 In a plot of the solvent spectral shift against polarisability (see Fig. 2), the deviations from the best-fit line are larger than the estimated errors in AvObs.Solvent groupings which show linear behaviour can be found, depending on whether the solvents are halogenated or deuteriated and contain satu- rated or unsaturated groups. For example, the perhalogenat- ed benzenes, C6F, (17) + C6F51(20) and perhaps c,c1,(14), lie on a line of similar gradient to the aliphatic perhalogenat- ed solvents, C,F,Cl, (ll), C,F,Br, (12), CFCl, (6),CBr,F, (7), CCl, (5) and possibly CS, (l), but with a different inter- cept.(Numbers in parentheses refer to Tables 1 and 2 and Fig. 2,4 and 5.) McRae introduced a solvent-dependent term into the constant K to account for differing intercepts K = AL, + B (11) where Lo is the weighted mean absorption wavelength of the solvent.,, Inclusion of this term does not lead to an improve- ment in the fit for our singlet oxygen data. For weak transitions, Longuet-Higgins and Pople derived a formula to predict the magnitude of the solvent-induced shifts for a non-polar solute in a non-polar solvent (dispersion forces).33 For dilute solutions, the general red shift is proportional to the polarisability, c(B, of the solvent and the predicted solvent shift rapidly decreases as the dis- tance R separating the solvent and solute increases.The shift is also proportional to aA, the polarisability of the solute, the number of solvent molecules N (in a random orientation) surrounding the solute and the energy Ei of the transition. The spectral shifts for interactions between polar or non- polar solutes and polar or non-polar solvents have also been derived for vdW complexes.34 The difference in this approach is that the clusters of solvent molecules in the cage surround- ing the solute are at particular orientations. For singlet oxygen3 if a second term involving the transition moment for the for- bidden transition O,('AJ + 0,(3Z;) is assumed to be negli- gible. If it is assumed that six solvent molecules are equidistant from the oxygen molecule and they are symmetri- cally arranged in an octahedral arrangement, with the pairs of solvent molecules lying on the x, y and z axis, and the polarisability tensor of molecular oxygen a,, = ctx,ii + ctyyj+ a,, kk and a, = a,,,, = a,, = 1/3aO0,the solvent spectral shift is given by36 AV = a00 C~BNEi 8R,6 The shift predicted in benzene using this approach was calcu- lated to be ca.50 cm-for a complex radius, R, , of 3.6 in good agreement with the reported experimental values. 6* As the theory developed for vdW complexes successfully predicts the solvent spectral shifts, we used this model to cal- culate shifts for each of the solvents used. The polarisability (volume) of a solvent is where V, is the molar volume, calculated from the mass and densities listed in the suppliers catalogues (mainly Aldrich), J.CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Table 2 Model parameters for calculations solvent "D a (1) (3) (5) (7) (2) (4) (6) (8) (9) (lo) (11) (12)(13) (14) (15) (16) (17)(18)(19) (20) cs, CD2C12 CC14 CBrzF-2 CD,OD CDCI, CC1,F CD3CN CF,CO,D c2c14 C2F3C13 C2F4Br2 C2D,C0 c4c16 C,D,N C6D6 C6F6 C6F,Cl C6F,Br C6F51 1.627 1.326 1.422 1.444 1.460 1.382 1.402 1.341 1.285 1.506 1.358 1.370 1.355 1.555 1 SO8 1.499 1.377 1.423 1.449 1.496 1.252 60.14 40.62 63.84 80.26 96.50 91.95 91.35 52.23 77.05 102.2 119.0 119.5 156.6 73.54 80.13 88.59 115.4 129.2 124.7 133.4 202.5 2.3 1 2.05 2.37 2.55 2.73 2.59 2.59 2.24 2.51 2.82 2.85 2.85 2.48 3.29 2.61 2.68 2.93 3.02 3.06 3.13 3.45 8.45 3.25 6.43 8.45 10.48 8.48 8.82 4.35 5.45 12.04 10.36 10.71 6.35 19.92 9.47 10.3 1 10.52 13.04 13.26 15.45 12.77 1.493 106.3 2.87 12.24 1.313 24 1 3.81 18.6 1.335 307 4.20 25.2 1.338 378 4.5 1 31.2 Refractive index at the average D-line of sodium (16 969 cm-') at 20 "C.55.1 64.6 3.27 27.5 32 51.1 2.90 16.2 37.4 42.5 3.35 19.0 35.6 35.7 3.61 19.0 33.2 29.6 3.86 18.1 23.0 33.2 3.66 18.0 24.7 34.3 3.66 18.7 34.0 40.0 3.17 15.8 11.6 25.5 3.55 13.0 35.5 27.8 3.99 18.3 17.0 22.6 4.03 15.1 18.9 23.3 4.03 15.6 33.4 32.0 3.51 15.9 38.2 18.4 4.65 16.2 50.8 35.1 3.69 19.5 44.0 32.5 3.79 19.1 15.0 19.5 4.14 13.7 19.8 20.1 4.27 15.1 23.3 18.8 4.33 14.5 29.7 19.1 4.43 15.4 0.9 8.8 4.88 8.5 43.6 25.6 4.06 17.4 0.2 7.1 5.39 7.1 0.6 5.4 5.94 5.4 0.5 4.3 6.38 4.3 Hard-sphere radius, calculated from the vdW volumes ( Vw),esti-mated using Bondi's tables.,' Calculated shift for model 1: six solvent spheres in an octahedral close-packing arrangement around oxygen, AvCalc= 9384a'lR:.Minimum radius of the complex when solvent spheres are close-packed : R: = 2r&. Calculated shift for model 2: R, = ro2 + rhs, to,= 1.46 A. N, is the Avogadro constant and n is the refractive index at the average D-line of sodium at 20°C, also from the suppliers catalogues. The distance between the solvent and oxygen molecules was calculated from the vdW volumes estimated using Bondi's tables37 and by assuming that the solvents were hard spheres of radius, rhs.The parameters used to cal- culate the solvent spectral shift are listed in Table 2, for each solvent.As a starting point (model l), the radius, R,, of the complex was calculated by assuming that the solvent mol- ecules were close-packed hard spheres (R, = 2r;J and the vdW volume of the oxygen molecule (13 cm3 mol-')37 was not taken into consideration. The calculated solvent spectral shifts for the (0-0) transition, using E, = 7882.4 cm-' and aoo = 1.58 A3,lS are listed in Table 2 and are shown plotted against the observed shifts in the peak maxima in Fig.5. The agreement between the calculated and the observed shifts is 015 / 014 7L9 L/ t /.--11 .-0 10 20 30 40 50 60 70 calculated peak shift/cm-' Fig. 5 Plot of the calculated spectral shift against the observed spectral shift, using model 1 (see text and Table 2) encouraging, although there are still substantial deviations from AvObsfor some solvents. The predicted shift is obviously highly dependent on the choice of the vdW complex radius, R,. This parameter was recalculated allowing for the oxygen volume (model 2) using R, = rhs+ ro2, with ro2 = 1.46 A. The solvent shifts deter- mined with this larger complex radius (excluding the per- fluorocarbons, which have sufficiently large free cavities to accommodate the oxygen molecule2*) are also listed in Table 2. The relaxation of the complex radius by 0.2-0.6 8, for the oxygen molecule leads to an improvement between the calcu- lated and observed shifts for only CF,CO,D (9), C,F, (17), C2F,Cl, (ll), C,F,Br, (12), CC1,F (6) and CBr,F, (7) and larger deviations result for the other solvents.Alternatively, for those solvents where the calculated shift is larger than the observed shift, an improved fit may be obtained if the number of solvent molecules, N, in the complex is varied and if the actual structure of the solvent is taken into consideration. The assumption that the linear solvent CS, approximates a hard sphere is a poor one. If four CS, solvent molecules are arranged collinear to and around the oxygen molecule in a square-planar arrangement, the dis- tance of closest approach is then the sum of the vdW radii of oxygen (1.4 A) and carbon (1.7-1.78 A).The calculated shift is then in the range 59.3-50.9 cm-', straddling the observed shift of 54.4 cm-'. Other solvents which may pack close enough together in 4:l complexes to account for the observed shifts are methanol (2), dichloromethane (3) and acetonitrile (8). There still remain, however, a number of sol- vents (those lying above the line in Fig. 5) which apparently cannot be arranged close enough to the oxygen molecule (in any stoichiometry) to account for the observed shifts. This suggests that there must be additional attractive forces involved in stabilising the complex. The theories we have used to predict the solvent spectral shifts consider only the non-specific dispersion forces (instantaneous dipole-induced dipole forces).In polar sol- J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 vents the additional dipole-induced dipole forces are assumed to be negligible, as are any higher-order multipolar forces, as the term considering these forces is dependent on the square of the extremely weak transition moment.35 The observation of red shifts in the maxima of the (0-0) transition in perfluorocarbons, which are much smaller than predicted for these solvents, suggests that there could be weak repulsive interactions to be considered. Syific interactions such as hydrogen bonding and exchange interactions could be impor- tant in some solvents.Particularly large deviations between the observed and calculated shifts were obtained for benzene (16), toluene (22), pyridine (15) and hexachlorobutadiene (14); solvents with low ionisation potentials38 and low-lying charge-transfer state^.^^.^' The ionisation potential of tetra-chloroethene (10) is also low and the ionisation potential may be expected to decrease along the series C6F6 (17) +C6F51 (20). We suggest that in solvents of low ionisation potential, weak charge-transfer interactions between each solvent in the vdW complex and singlet oxygen leads to a small additional stabilisation (ca. 10-20 cm-') of the complex. It has been calculated that the singlet state of the complex between the solvent molecules and 02('A,) could be stabilised by 10-30 cm-',if the charge-transfer state lies 4000 cm-' above the triplet state of the solvent.41 Recent measurements of the singlet oxygen lifetimes at high pressures also indicate the existence of charge-transfer interactions between singlet oxygen and solvents with low ionisation potential.42 Solvent Effects on tbe Vibrational Frequency Our observation of a solvent-dependent decrease in the vibrational spacing of the ground state of oxygen suggests the existence of a weak ground-state complex between oxygen and some of the solvent molecules. In an NMR study of the interaction of ground-state oxygen with benzene and hexa- fluorobenzene, no evidence for complex formation was found.43 A cubic lattice of C6F6 molecules at a distance of 4.34-4.60 A from oxygen was, however, suggested in this work, in agreement with the complex radius we calculated for singlet oxygen and six hexafluorobenzene molecules.In other NMR studies,44 interactions in the ground state were appar- ently observed. The appearance of a new absorption band on bubbling oxygen into some solvents is well known and has been attributed to the formation of contact charge-transfer complexes.39 These complexes were predicted to be disso-ciative (binding energy <100 cm-'), but recent studies of the interaction between gaseous oxygen and benzene indicate the formation of a discrete weakly bound ground-state complex, with a stabilisation energy of 290 cm-1.45 In C6D6, we observed an anomalously small decrease in the vibrational spacing of the ground state of oxygen, probably due to the weak intensity of the (0-1) band and the presence of inter- fering background radiation.Bandshapes The observed bandwidths of the 02('Ag) +02(3Eg-) tran-sition are also solvent dependent and increase as the observed solvent spectral shifts increase. The same factors responsible for the stabilisation of solvated singlet oxygen are also, to some extent, responsible for the increased bandwidth. As the singlet oxygen spectra in perfluorocarbons indicate that no complex is formed, it is interesting to compare the bandshapes in these solvents with the bandshape in the gas phase at low pressure. The singlet oxygen bandshape in C14F24 is essentially symmetric and no rotational structure was observed at a resolution of 2 cm-'.If the free cavities in the perfluorocarbons were sufficiently large to allow 'free' rotation of the oxygen molecule, a bandshape similar to that of the gas-phase spectrum, but with blurred P and R branches might be expected. However, the rotation is prob- ably random 'flip-like' in nature (rotational diffusion) because of intermolecular collisions with both the solvent and oxygen molecules. In the gas phase, the bandwidths of the singlet oxygen transitions (in both absorption and emission spectra) are pressure dependent, owing to underlying contin- uous bands from collision complexes (with either oxygen or an added gas molecule) overlapping the discrete band from isolated rnole~ules.~~-~~ As the 02('Ag) +02(3Cg-)transition becomes spin-allowed in the bimolecular complex between singlet and triplet oxygen, the singlet oxygen emission observed in perfluorocarbons is from this oxygen complex.Interaction of singlet oxygen with the more polarisable sol- vents in the vdW complex results in asymmetric broadening of both the (0-0) and (0-1) transitions to the red. The approximate linear correlation of Al,? with AvObs suggests that most of the increase in the bandwidths in the more pol- arisable solvents is due to vdW broadening. The rotation of singlet oxygen in the solvent cage of more polarisable sol- vents must be highly restricted and the observed broadening must be a consequence of a vibrational relaxation mechanism in the vdW complex.Theory predicts that the emission band- width of singlet oxygen is dependent on two variables, the displacement, Aj, and the optical frequency, oj,of the inter- molecular vibrational modes of the 'supermolecular ' complex.50 As the intermolecular interactions are weak, the low-frequency intermolecular vibrational modes may be treated separately from the intramolecular modes, if the monomer subunits are considered to be rigid.51 However, neither of the two variables are quantifiable at this stage. (0-0) :(0-1) Intensity Ratio The ratios of the intensities of the (0-0):(0-1) transitions were larger than those previously reported in both the solu- tion and gas phase. However, in this study all the emission spectra were corrected for the instrumental response function and in some solvents, where the (0-1) intensity was weak (such as C6D6), the peak intensity was also corrected for the underlying background emission.The small decreases in the ratio of the intensities appears to correlate with the other observed solvent effects. A decrease in the ratio of the inten- sities, by a factor of more than ten, has previously been reported in the gas phase, as the pressure of oxygen was increased.48 The ratio of intensities, extrapolated to zero pressure was 50: 1, in agreement with previous determi-nations of 50 :126 and 76.4 :l.52It has been reported that only oxygen molecules can induce a change in the ratios of inten~ities,~~.~~although a broad, collision-induced emission has recently been reported with dinitrogen oxide as a foreign gas, for both the (0-0) and (0-1) transition^.^^ The change in the Franck-Condon factors is a further subtle effect of the formation of van der Waals complexes.A.N.M. and T.G.T. thank the Scottish Home and Health Department and the Cancer Research Campaign for financial support. We thank Prof. Sheng. Lin (Arizona State University) for helpful discussions. References 1 Singlet Oxygen, ed. A. A. Frimer, CRC Press, Boca Raton, 1985, vol. 1. 2 S. Y. Egorov, V. F. Kamalov, N. I. Koroteev, A. A. Krasnovsky Jr., B. N. Toleutaev and S. V. Zinukov, Chem. Phys. Lett., 1989, 163,421. 1072 J. CHEM. SOC. FARADAY TRANS., 1994, VOL.90 3 4 R. Schmidt, Chem. Phys. Lett., 1988, 151, 369. R. Schmidt and E. Afshari, J. Phys. Chem., 1990,94,4377. 31 32 C. Long and D. R. Kearns, J. Chem. Phys., 1973,59,5729. E. G. McRae, J. Phys. Chem., 1957,61,562. J. R. Hurst and G. B. Schuster, J. Am. Chem. SOC., 1983, 105, 5756. 33 H. C. Longuet-Higgins and J. A. Pople, J. Chem. Phys., 1957,27, 192. 6 7 8 M. A. J. Rodgers, J. Am. Chem. SOC., 1983,105,6201. R. Scurlock and P. R. Ogilby, J. Phys. Chem., 1987,91,4599. R. Schmidt and H-D. Brauer, J. Am. Chem. SOC., 1987,109,6976. 34 35 W. E. Henke, W. Yu, H. L. Selzle, E. W. Schlag, D. Wutz and S. H. Lin, Chem. Phys., 1985,97,205. S. H. Lin, J. Lewis and T. A. Moore, J. Photochem. Photobiol. A: 9 11 12 13 14 16 17 18 19 21 E.Afshari and R. Schmidt, Chem. Phys. Lett., 1991,184, 128. A. A. Gorman, I. Hamblett, C. Lambert, A. L. Prescott, M. A. J. Rodgers and H. M. Spence, J. Am. Chem. Soc., 1987,109,3091. A. P. Losev, I. M. Byteva and G. P. Gurinovich, Chem. Phys. Lett., 1988, 143, 127. A. P. Losev, I. N. Nichiporovich, I. M. Byteva, N. N. Drozdov and I. F. A1 Jghgami, Chem. Phys. Lett., 1991,181,45. A. A. Gorman, A. A. Krasnovsky Jr. and M. A. J. Rodgers, J. Phys. Chem., 1991,95,598. P-T. Chou and A. U. Khan, Chem. Phys. Lett., 1984,103,281. K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure, Van Nostrand Reinhold, New York, 1979, vol. 4. A. Bromberg and C. S. Foote, J. Phys. Chem., 1989,93,3968. I. M. Byteva, A. P. Gurinovich, A. P. Losev and A. V. Mudryi, Opt.Spectrosc. USSR, 1990,68, 317. I. B. C. Matheson and J. Lee, Chem. Phys. Lett., 1971,8, 173. R. J. Bell, Introductory Fourier Transform Spectroscopy, Aca-demic Press, New York, 1972. P. Biggs, F. J. Holdsworth and R. P. Wayne, J. Phys. E: Sci. Znstrum., 1987, 20, 1005. A. U. Khan and M. Kasha, Proc. Natl. Acad. Sci. USA, 1979,76, 36 37 38 39 40 41 42 43 44 45 46 47 Chem., 1991,56,25. J. Lewis, S. H. Lin and T. A. Moore, personal communication, 1991. A. Bondi, J. Phys. Chem., 1964,68,441. CRC Handbook of Chemistry and Physics, ed. R. C. Weast, CRC Press, Boca Raton, FL, 61st edn., 1981. H. Tsubomura and R. S. Mulliken, J. Am. Chem. SOC., 1960,82, 5966. R. D. Scurlock and P. R. Ogilby, J. Phys. Chem., 1989,93,5493. A. U. Khan and D. R. Kearns, J. Chem. Phys., 1968,48,3272. M. Okamoto and F. Tanaka, J. Phys. Chem., 1993,97,177. J-J. Delpuech, M. A. Hamza, G. Serratrice and M-J. SteM, J. Chem. Phys., 1979,70,2680. G. P. Gurinovich, Bull. Acad. Sci. (USSR) Phys. Ser., 1988, 52, 149. E. A. Gooding, K. R. Serak and P. R. Ogilby, J. Phys. Chem., 1991,95,7868. R. M. Badger, A. C. Wright and R. F. Whitlock, J. Chem. Phys., 1965,43,4345. R. P. Blickensderfer and G. E. Ewing, J. Chem. Phys., 1969, 51, 873. 22 23 24 26 27 28 6047. K. I. Salokhiddinov, B. M. Dzhagarov, I. M. Byteva and A. P. Gurinovich, Chem. Phys. Lett., 1980, 76, 85. A. A. Krasnovsky Jr., Photochem. Photobiol., 1979,29,29. P. Suppan, J. Photochem. Photobiol., A: Chem., 1990,50, 293. A. U. Khan, Chem. Phys. Lett., 1980,72,112. S. H. Whitlow and F. D. Findlay, Can. J. Chem., 1967,45,2087. A. Zipp and W. Kauzmann, J. Chem. Phys., 1973,59,4215. W. W. Robertson and A. D. King Jr., J. Chem. Phys., 1959, 31, 473. 48 49 50 51 52 J. Wildt, E. H. Fink, P. Biggs and R. P. Wayne, Chem. Phys., 1989,139,401. J. Wildt, E. H. Fink, P. Biggs, R. P. Wayne and A. F. Vilesov, Chem. Phys., 1992,159, 127. Y. Y. Lin, Z. T. Chu and S. H. Lin, J. Photochem. Photobiol. A: Chem., 1988,44,229. E. Knozinger and 0.Schrems, in Vibrational Spectra and Struc- ture, ed. J. R. Durig, Elsevier, Amsterdam, 1987, pp. 141-225. M. Halmann and I. Laulicht, J. Chem. Phys., 1965,43,438. 29 A. Maciejewski, J. Photochem. Photobiol. A: Chem., 1990,51,87. N. S. Bayliss, J. Chem. Phys., 1950, 18, 292. Paper 3/07289D; Received 9th December, 1993

ISSN:0956-5000    

DOI:10.1039/FT9949001065

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. CHEM. SOC. FARADAY TRANS., 1994, 90(8), 1073-1076 Photophysical Studies of Substituted Porphyrins Paul Charlesworth and T. George Truscott* Chemistry Department, Keele University, Staffordshire, UK ST5 5BG David Kessel Pharmacology and Medicine, Wayne State University School of Medicine, Detroit, MI 4820 1, USA Craig J. Medforth and Kevin M. Smith Department of Chemistry, University of California, Davis, CA 95616, USA Ground-state, fluorescence and triplet-state parameters, together with singlet oxygen quantum yields are pre-sented for two porphyrins with extensive substituents at both the p-pyrrole and meso positions. The relevance of the results to the photodynamic therapy of cancer is discussed. Recently there has been considerable interest in the intro- duction of steric hindrance to porphyrins and phthalocya- nines and the effect which this has upon the photophysical properties of the molecule.' Deviations from planarity in photosynthetic chromophores such as the chlorophylls have been suggested to be pivotal in their behaviour, and in model porphyrins, steric hindrance between B and meso substituents has been shown to induce non-planar conformations.Theo- retical calculations based on some photosynthetic reaction centres have shown that changes in the conformation of the molecule would affect it in such a way as to change the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals, leading to a change in their photo-chemical properties.'~~ It is also thought that steric hindrance may be the way forward to a reduction in porphyrin and phthalocyanine aggregation, which would be important if such molecules are to be used as sensitizers of singlet oxygen in the photodynamic therapy of cancer. Studies of two symmetrically substituted porphyrins having substituents at both the /3-pyrrole and meso positions are presented.Dodecaphenylporphyrin (DPP) [Fig. l(a)], has all the p-pyrrole and meso positions occupied by phenyl rings, and 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenyl-OETPP Fig. 1 Structuresofdodecaphenylporphyrin,DPP and 2,3,7,8,12,13, 17,18-octaethyl-5,10,15,20-tetraphenylporphyrin,OETPP porphyrin (OETPP) [Fig. l(b)] has all the B-pyrrole positions occupied by ethyl groups and the meso positions occupied by phenyl rings.Under the conditions studied in this work both porphyrins exist entirely as monomers. However, we choose methanol and benzene as solvents to allow study of the cationic and neutral forms of the porphyrins, respectively. Previous work by Medforth and Smith concerned the con- formational structure of DPP4 and the zinc complex and free base of OETPP.4 By X-ray crystallography, these workers demonstrated' that both of the molecules adopt a non-planar saddle conformation with alternating pyrrole rings pointing up or down. They also showed, by variable-temperature proton NMR experiments, that the molecules are also non- planar in solution and may undergo a macrocyclic inversion process. Experimental DPP and OETPP were synthesized as described previo~sly~.~and used without further purification. All non- deuteriated solvents were of HPLC grade and were obtained from Aldrich Chemicals.Deuteriated methanol was obtained at 99.9% D from Goss Chemicals. Absorption spectra were measured using a PC-controlled Perkin-Elmer Lambda 2 spectrophotometer. Fluorescence spectra were measured using a PC-controlled Perkin-Elmer LS50 spectrofluorimeter. Fluorescence lifetime studies were made at the SERC Daresbury Synchrotron facility on station 12.1 (time-resolved spectros~opy).~*~ The time resolution of this facility is ca. 100 ps. Measurements were made in benzene and methanol; in all cases the absorbance at the excitation wavelength was <0.1 in order to reduce problems with inner filtering.The triplet studies were made, using nitrogen-saturated benzene and methanol solutions, by laser flash photolysis with 355 or 532 nm excitation from the frequency-tripled or frequency-doubled outputs of an Nd : YAG laser (Spectron Lasers, 16 ns pulse width). Triplet spectra presented are nor- malised to a laser energy of 1. The triplet-state molar absorp- tion coefficients were determined to +lo% by the complete conversion method, and intersystem crossing quantum yields were determined to f10% by the comparative method with anthracene in cyclohexane as the actinometer.'-' Singlet oxygen was monitored via its near-IR luminescence at 1270 nm due to the 02('Ag)+Oz(3Zi)radiative tran- sition, following 532 nm laser excitation from the frequency- doubled output of the Nd: YAG laser with a detection system comprising a germanium photodiode and Judson amplifier, linked via a Tektronix digital oscilloscope to a PC for data analysis.Singlet oxygen yields were measured to f10% relative to meso-tetraphenylporphine (Porphyrin Products) in benzene (djA = 0.63)," and haematoporphyrin (Porphyrin Products) in methanol (aA= 0.53)13as standards. Biological Studies Murine leukemia L1210 cells were grown in Fischer's medium (GIBCO, Grand Island, NY) supplemented with 10% horse serum and antibiotics. Incubations were carried out in growth medium with 20 mmol dm-3 HEPES pH 7.2 replacing sodium hydrogencarbonate. To introduce porphyrins into cells a 10 mmol dm-3 solu-tion in N,N'dimethylformamide was added to cell suspen-sions in the incubation medium (10% serum).The level of the solvent so used is not sufficient to affect any parameter being measured. Also, note the hydrophobicity of the drugs them-selves is not a problem with regard to clinical use. Cells were incubated with sensitizers for 30 min at 37 "C, collected by centrifugation, suspended in fresh medium at 10 "Cto minimize temperature-dependent repair systems, and irradiated (time = 3 min) using a 600 W QH lamp (5 mW cm-', 1800 J m-'). The wavelength of irradiation was limited to 630-850 nm by cut-off and heat-absorbing filters and further attenuated by a 10 cm layer of water. The resulting fluence rate was measured with a calibrated EG & G 450-1 radiometer; this was calculated to be 2.1 f0.15 mW cm-' per 10 nm bandwidth over the range 650-750 nm.Results and Discussion It is well established that the two porphyrins studied are strong bases. In methanol they exist as cations, while in benzene they are in the neutral form but can be readily con-verted to the cationic form. From the ground-state spectra (Fig. 2) it is clear that solvent plays an important role in the photophysical properties, and this is shown to some extent in many of the studies we have made on these molecules. The effect of changing solvent from benzene to methanol is to cause a loss of the Q bands in the region 500-800 nm which 1.o 0.8 0.6 , ,\ 0.4 \ 7 \ f\ \ I \ \ 0.2 \ L 0 J.CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 are replaced by one band at ca. 730 nm and accompanied by a shift in the wavelength and/or a broadening of the Soret band, this may be attributed to protonation of the porphyrin, as an effect which has been noted previously for OETPP' and DPP.4 The fluoresence maxima were observed for OETPP at ca. 758 nm in methanol, and ca. 755 nm in benzene; with those for DPP being at ca. 796 nm in methanol and ca. 780 nm in benzene. The low fluorescence quantum yields obtained for these compounds (OETPP: djf xO.005 in methanol and @jf x0.004 in benzene; DPP: @jf x0.002 in methanol and @jf x0.003 in benzene) correlate well with the time-resolved studies made at the Daresbury Laboratory.Lifetimes obtained for OETPP (Aex = 480 nm Aem = 760 nm) were 0.21 ns (91.5%),0.37 ns (8.5%) in methanol and 0.92 ns (ca. 100%) in benzene. With the lifetimes for DPP (Aex = 460 nm, A,, = 780 nm) being <0.1 ns (ca. 90%), 0.28 ns (ca. 10%) in meth-anol and 0.82 ns (ca. 100%) in benzene. The biexponential lifetimes in methanol are of the order of 100-400 ps, suggest-ing that protonation leads to enhanced deactivation of the energy, either through intra-or inter-molecular interactions, providing more than one possible pathway for the rapid energy loss. The reason for the minor (<10%) component in methanol is not clear since the porphyrins exist as the mono-mers in this solvent and mixtures of free base with the dica-tion would not seem to account for the data. The position of the triplet maximum for each of the indi-vidual compounds is largely unaffected by the choice of solvent in this study.For DPP (Fig. 3) in benzene the maximum is at ca. 500 nm (E~x72200 dm3 mol-I cm-') and in methanol is at ca. 510 nm (complete conversion not achieved). For OETPP (Fig. 4) the maximum is at ca. 550 nm (E~x21 OOO dm3 mol-' cm-')in benzene and at ca. 550 nm (complete conversion not achieved) in methanol. As with the singlet state lifetimes, the triplet state lifetimes are rather short (DPP, z x2.5 ps in methanol and 7 x20 ps in benzene; OETPP, z x2.8 ps in methanol and 7 x20 ps in benzene) and the triplet quantum yields also rather small (DPP, di, x 0.29; OETPP, @jT x 0.34 in benzene) compared to planar 2.0 2.0 (') ,-, 'I I I 1.5 I 1.o 1.o \ Y nrn I \4-'5 0.5 \ 0.5I e i 3 0.3- .0.3 x5 r I\ 0.2- I '- -0.2 I '\ z 0.10.1 --// \\ ' -0.1 A/nm 0 300 400 500 A/n m -, 600 0 700 800 Fig.2 Ground-state absorption spectra for (a)DPP in benzene (free base); (b)DPP in methanol (dication+free base); (c) OETPP in benzene (free base) and (d)OETPP in methanol (dication) J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 1075 0.10 (a 1 A 0.10 benzene. The value for S, (the fraction of triplets which when quenched by ground-state oxygen lead to singlet oxygen) was 0.051 iz 10.05 calculated according to the equation I This takes into account the short lifetimes of the triplet state16 and yield S, x 0.6, which is somewhat lower than normally expected for a porphyrin (ca.0.8). This not only provides an explanation for the lower @, values, but suggests that processes other than energy transfer occur in the excited- state oxygen complex. Whilst these yields are low relative to 0.2 their standards (TPP @, x 0.63 in benzene and HP.2HC1 @, x 0.53 in methanol) they are still sufficient as potential 0 sensitizers for photodynamic therapy. Also, as there is a red shift of the n-x* transition, this leads to a molecule with a lower singlet-state energy and hence a -0.2 -0.2 lower triplet-state energy than most porphyrins. Further- O.:: more, if the energy of the triplet state is very close to that of oxygen then the ability of the porphyrin to sensitize singlet oxygen formation may be reduced.It would seem unlikely that sterically hindered triplet energy transfer to the ground- state molecular oxygen would be responsible for the decrease 1-0.64 400 1-0.6 in the quantum yield because triplet energy transfer is largely 350 450 500 550 600 650 700 unaffected by steric hindrance, since energy transfer at van R/nm der Waals separation is so rapid.17 However, Scaiano et Fig. 3 Triplet minus singlet difference spectra for (a) DPP in all8 suggest that slower triplet energy transfer may be a func- benzene and (b)DPP in methanol tion of stereoelectronic factors rather than steric hindrance and may provide an indicator to the nature of the triplet porphyrins such as meso-tetraphenylporphine (z x 100 ps, state, be it n,x*, z,n*,a combination, or even that there are djf x 0.1 @= x 0.8).This may be attributed, as discussed by fewer accessible orientations allowing the orbital overlap and Tsuchiya" to intramolecular energy necessary for energy transfer. We found the rate of reaction of Takeda et ~1.'~ transfer, leading to energy dissipation as heat, or possibly OETPP and DPP triplet states with ground-state molecular intramolecular electron transfer between phenyl groups. oxygen was not significantly slower than one-ninth the Singlet oxygen yields obtained by time-resolved lumines- diffusion-controlled rate in benzene (DPP, k, x 1.6 x lo9 cence techniques are OETPP, @, x 0.25 in MeOD; @, x dm3 mol-' s-'; OETPP, k, x 1.2 x lo9 dm3 mol-' s-l in 0.24 in benzene and DPP, a, x 0.24 in MeOD; @, x 0.19 in benzene).However, in methanol (DPP, k, x 0.25 x lo9 dm3 benzene. The @, values are lower than the @= values in mol-' s-'; OETPP, kqx0.31x lo9 dm3 mol-' s-') we found the rate constant to be almost one order of magnitude 0.4 slower. We did, however, find that the relative yields of singlet oxygen were comparable or only mariginally higher 0.2 for both porphyrins in methanol than in benzene. Thus, despite the rather short triplet lifetimes in methanol, the 0 higher oxygen concentration in this solvent leads to substan- tial singlet oxygen production. -0.2 Biological Studies-0.4 Extracellular levels of the different sensitizers required to -0.6 photosensitize lethally 50% of a cell population (EC,,V) were determined.The corresponding cellular levels were estimated -0.8 from distribution ratios as described above. Viability was 0.2 assessed by the MTT assay" carried out after a 3 day incu- bation of cells in culture. This latter procedure provides infor- mation on photodamage which is well correlated with results Oa2i;'..-----I 0 0 of clongenic assays.20-2' For this assay, cells were diluted 50-fold with fresh medium. The concentration of photo-sensitizers was sufficiently reduced so that no 'dark' toxicity -0.2 was observed. Table 1 Cell kill data for murine leukemia L1210 cells with DPP and OETPP -0.41-JLJ-0-4350 400 450 500 550 600 650 700-0.6 -0.6 sensitizer EC,,/pmol dm-' IC,,/pmol dm-' DR A/nm DPP 30 40 1.3 OETPP 5 10 2.0 Fig.4 Triplet minus singlet difference spectra for (a) OETPP in PP 1 8 8.8 benzene and (b)OETPP in methanol EC,, (Table 1) is the extracellular drug level needed to photosensitize lethally 50% of a cell population, and the IC5, value represents the corresponding intracellular drug concen- tration, calculated from the distribution ratio (DR) which represents the ratio of intracellular/extracellular drug levels. Data represent the average of three determinations which dif- fered by < f10% of the numbers shown. Conclusion The similarities of the photophysical properties between the two molecules may be mirrored in their biological activities where DPP, although requiring a four-fold increase in intra- cellular level to yield the same phototoxic effect as OETPP, shows a level of activity almost identical to that of OETPP when the differences in absorption coefficient are taken into account.Furthermore, whilst the photophysics suggests that both drugs would be equally good at producing phototoxic products, DPP may localise at sites more resistant to cyto- toxic intermediates than the site of OETPP binding. Unfor- tunately, the fluorescence lifetimes are so short that it is not possible to identify the sites of localisation accurately from fluorescence microscopy. By comparison when a 1 pmol dm-3 aluminium phthalocyanine solution is used, giving a distribution ratio of about 60, hence an intracellular drug level of about 60 pmol dm-3, irradiation for 15 s is sufficient to kill 50% of the cells, which is an order of magnitude less than required by DPP for the same cell kill.Also, when a 1 pmol dm-3 concentration of protoporphyrin is used, resulting in a distribution ratio of 8, hence an intracellular drug level of 8 pmol dm-3, irradiation for 3 min is sufficient to reduce the viability by 50%. This is approximately the same value as was obtained with OETPP, indicating that non-planarity does not necessarily interfere with photo-dynamic efficacy. P.C. and T.G.T. acknowledge the Cancer Research Campaign (UK) for financial support and T.G.T.also thanks the E.E.C. P.D.T. EURONET (ERBCHRXCT930178) for financial support. C.J.M. thanks the Fulbright commission (Travel Scholarship) and the Associated Western Universities (Post- J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Doctoral Fellowship). K.M.S. acknowledges a grant from the National Science Foundation. (CHE-93-05577). D.K. acknowledges NIH grant CA 52997. References 1 B. D. Rihter, M. D. Bohorquez, M. A. J. Rodgers and M. E. Kenney, Photochem. Photobiol., 1992,55, 677. 2 K. M. Barkigia, D. M. Berber, J. Fajer, C. J. Medforth, M. W. Renner and K. M. Smith, J. Am. Chem. SOC., 1990,112,8851. 3 K. M. Barkigia, L. Chantranupong, K. M. Smith and J. Fajer, J. Am. Chem. SOC., 1988,110,7566. 4 C. J. Medforth and K.M. Smith, Tetrahedron Lett., 1990, 31, 5583. 5 C. J. Medforth, M. 0. Senge, K. M. Smith, L. D. Sparks and J. A. Shelnutt, J. Am. Chem. SOC., 1992,114,9859. 6 R. Sparrow, R. G. Brown, E. H. Evans and D. Shaw, J. Chem. SOC.,Faraday Trans. 2,1986,82,2249. 7 H. Winick, Sci. Am., 1987,257,88. 8 R. Bensasson and E. J. Land, Trans. Faraday SOC., 1971, 67, 1904. 9 R. V. Bensasson, E. A. Dawe and E. J. Land, J. Chem. SOC., Faraday Trans. I, 1977,73,1319. 10 I. Carmichael and G. L. Hug, J. Phys. Chem. Ref: Data, 1986,15, 1. 11 D. Lavelette, R. Bensasson, B. Amand and E. J. Land, Chem. Phys. Lett., 1971, 10, 331. 12 R. Bonnett, D. J. McGarvey, A. Harriman, E. J. Land, T. G. Truscott, and J. Winfield, Photochem. Photobiol., 1988,48,271. 13 R. W. Redmond, K. Heihoff, S. E. Braslavsky and T. G. Truscott, Photochem. Photobiol., 1987,45,209. 14 J. Takeda, 0.Toshie and M. Sato, Chem. Phys. Lett., 1991, 183, 384. 15 S. Tsuchiya, Chem. Phys. Lett., 1990, 169, 608. 16 C. Knox, E. J. Land and T. G. Truscott, J. Photochem. Photo- biol, B: Biology, 1988, 1, 315. 17 P. Wagner, J. M. McGrath and R. G. Zepp, J. Am. Chem. SOC., 1972,94,6883. 18 J. C. Scaiano, W. J. Leigh, M.A. Meador and P. J. Wagner, J. Am. Chem. SOC., 1985,107,5806. 19 R. A. Plumb, R. Milroy and S. B. Kaye, Cancer Res., 1989, 49, 4435. 20 A. P. McHale and L. McHale, Cancer Lett., 1988,41, 315. 21 D. Kessel, A. Morgan and G. M. Garbo, Photochem. Photobiol., 1991,54,193. Paper 3/05 169B;Received 26th August, 1993

ISSN:0956-5000    

DOI:10.1039/FT9949001073

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. CHEM. SOC. FARADAY TRANS., 1994, 90(8), 1077-1082 Model Calculations of Chemical Interactions Part 7.t-Role of Vicinal Delocalization in the Regiochemical Control of the Cycloaddition of Diazomethane and Formonitrile Oxide to Methyl Vinyl Ether August0 Rastelli and Marisa Bagatti Dipartimento di Chimica, Universita di Modena , 183 Via Campi, 4 1100 Modena, Italy Remo Gandolfi and Marina Burdisso Dipartimento di Chimica Organica, Universita di Pavia, 10 V. le Taramelli, 27100,Pavia, Italy In strict accordance with the preceding theoretical and experimental studies on diastereofacial selectivity, we undertook a study of regioselectivity in 1,3-dipolar cycloadditions; the examples chosen included the reactions of alkyl vinyl ethers with diazomethane, the most famous and difficult regiochemical experiment in the literature of 1,3-dipolar cycloadditions and one that has yet to find a well grounded explanation, and with formonitrile oxide, a small 1,3-dipole with a fairly high dipole moment that is capable of enhancing any eventual role of electrostatic effects.The cycloaddition of methyl vinyl ether (MVE) with diazomethane was checked experimentally and found to afford 3-methoxy-1-pyrazoline as the only characterized and highly abundant adduct, although the formation of minor amounts of the other regioisomer could not be ruled out definitely. Concerted transitions structures (TS) were calculated at different levels of theory: 3-methoxy-1-pyrazoline and 5-methoxy-2-isoxazoline were found, in agreement with experiment, to be the favoured regioadducts of the reactions with diazomethane and formonitrile oxide, respectively.In both cases the favoured transition struc- tures were 'earlier' than the unfavoured one, and had anticonformations of the 0-Me substituent, in spite of the lower stability of the anti conformation in free MVE. According to our analysis, the regioselectivity of MVE 1,3-dipolar cycloadditions and the main features of the transition structures can be explained as follows: the largest vicinal stabilization is traceable to the four-electron threecentre n conjugation between the n lone pair and the n bond of the allylic fragment 0-C-C, which is also largely responsible for the rotameric potential-energ# -ofile of MVE. In the TSs these vicinal interactions are differently perturbed, in the different regioisomeric a laches, the more favourable perturbation dictating the regiochemistry; in our examples, the favourable approach occurs when the C.-.X bond (X = N, 0) is formed on the substituted carbon atom.This very same perturbation is also the origin of the earliness of the favoured TS and of the consequent weakness of its incipinet bond stabilization. The conformational features of the TSs are significantly affected by electrostatic effects. In this series of papers' a procedure for the analysis of intra- molecular interactions has been introduced and extensively applied to the explanation of conformational preference,'".'.d double-bond pyramidalization' and diastereofacial selec- tivity in 1,3-dipolar cycloadditions."tf The procedure, which rests on the intuitive concepts of classical steric-electrostatic repulsions and of vicinal delocalizations, and makes use of an orthogonalized set of hybrid atomic orbitals (OHAO) for their evaluation, leads to a clear and consistent picture of the effects induced by single intramolecular interactions (or selec- ted groups thereof) and also affords insight into the role of specific interactions in determining particular aspects of the ground-state and the transition-state molecular structures.In particular, a detailed analysis of the transition structures (TS) of synlanti cycloadditions of a selected group of dipolarophi- les (norbornene, cis-3,4-dichlorocyclobutene,bicyclopentene and 2,3-dioxabicyclooctene) with formonitrile oxide shows that facial repulsion (steric and electrostatic), and vicinal- stabilizing delocalizations between the newly forming bonds and the bonds at the allylic positions, appear to be the factors ultimately controlling the difference in energy of the syn and anti reaction barriers.Stabilizing vicinal delocalizations between bonding and antibonding MO orbitals of the incipient bonds and the vicinal bonds have often been postulated, to be important driving forces for diastereofacial selectivity, although this has t Part 6: A. Rastelli, M. Bagatti and R. Gandolfi, J. Chem. SOC., Faraday Trans., 1993,89,3913. Inbeen de~puted.~-~ contrast with that proposal, vicinal repulsive interactions originating from closed-shell repulsions (Houk et al.'s staggered model5) and electrostatic interactions (Hehre and co-workers' modelling treatment6) have also been considered to play a dominant role.Therefore, by analogy with the strategy used for diastereo- facial selectivity, we decided to undertake an analysis of the factors influencing the regioselectivity in 1,3-dipolar cyclo- additions with particular reference to the possible role of vicinal delocalizations. The proposal to investigate the stabilizing vicinal inter- actions as a possible cause (or partial cause) of regiochemical selection is quite new, for these interactions have never been proposed explicitly in this field. The only attempts to explain regioselectivity in cycloadditions can be traced to qualitative arguments based on frontier molecular orbital (FMO) theory7" and on electrostatic interactions,* the two explana- tions being considered to be closely related to each other.g When electron-donating and electron-withdrawing groups are attached directly to an alkene, the frontier orbital ener- gies and coefficients undergo opposite variations which are used to understand changes in reactivity and regiochemistry.The same substituent effect alter electrostatic potentials, and so regioselectivities could equally well be explained in such terms. Alternatively, a regiochemical effect of the vicinal inter- actions between the incipient bonds and the bonds or lone pairs of the nearest-neighbour atom of the substituent can be postulated on the grounds that these interactions represent/ transmit the electron delocalization between the substituent and the alkene fragment.The different regiochemical approaches of 1,3-dipoles should induce different pertur- bations of this delocalization, the selected regiochemsity cor- responding to the more favourable (more stabilizing) alternative. Choice of Models The choice of models includes two 1,3-dipoles with low steric demand and very different electrostatic features, diazo- methane having a low dipole moment (1.4 Dt) and for- monitrile oxide a significantly larger one (3.1 D). As for the dipolarophile, we will start by considering the electron-rich substituted alkene, methyl vinyl ether (MVE), so as to chal- lenge our theoretical results with the most controversial regiochemical experiment present in the literature of 1,3-dipolar cycloadditions.Since 1973 FMO theory of cycloaddition regiochemistry has been adopted to explain all known experimental results; furthermore, any new regiochemical result produced in the last two decades has been claimed to agree the theory and has thus supported it. However, it has been asserted that the success of the theory also rests on the exceptional flexibility of its practical use" and on the general tendency to avoid clear predictions in favour of a posteriori explanations, factors which have in effect protected the theory against failure. As an example," the occurrence of an incorrect experimental result, i.e.the claimed formation of 4-butoxy-l- pyrazoline (Scheme 1; type A regiochemistry) in the cyclo- addition of butyl vinyl ether with diazomethane, led to rationalization of the theory. Soon after, Firestone" studied the reaction of ethyl vinyl ether and found the opposite regio- chemistry (3-ethoxy- 1 -pyrazoline, type B regiochemistry). The new result was readily accounted for by the same theory. Now we have at least three different explanations for the correct regiochemistry at our disposal: first, it has been stated as a fact7b that with electron-rich alkenes the regiochemical control is assumed by the dipole LUMO-alkene HOMO interaction (instead of the previously postulated dipole HOMO-alkene LUMO), which switches the prediction from 4- to 3-ethoxy- l-pyrazoline. A second explanation' ' postu-lates that a repulsive secondary orbital interaction between the nucleophilic C terminus of diazomethane and the donor substituent is able to steer the reaction centres to the opposite regiochemical approach.A third recent explanation' claims that distortions of the dipolarophiles in the TSs, due to closed-shell repulsions, are responsible for the FMO interactions which favour the experimental regioche- mistry. The possible role of electrostatic interactions in the regio- chemistry of 1,3-dipolar cycloadditions does not appear to have received any systematic attention. Accordingly, in order to enhance any effect of electrostatic repulsions as regioisornersA regioisorners B H-CEN->O anti 7--Hy+J Me-0 MeO/ MeO' Scheme 1 1 D (Debye) = 3.335 64 x lo3' C m.J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 regioselectivity-controlling factors we also considered for- monitrile oxide instead of diazomethane, since comparison of diazomethane and formonitrile oxide cycloadditions on the syn faces of cis-3,4-dichlorocyclobutene'4a*b and 2,3-dioxa- bicyclo[2.2.2]oct-5-ene' 4c revealed, both experimentally' and theoretically,"*fi' the increased importance of electro- static interactions. As for the regioselectivity data, nitrile oxides react with alkyl vinyl ethers to produce only 5-alkoxy-2-isoxazolines (type B regiochemistry).' 6b*c For example, a careful analysis (GC and 'H NMR) of the reaction of benzonitrile oxide with MVE showed that the regioselectivity is as high as 98%.17 Finally, the simplest alkoxy substituent was chosen (-OMe) both for economical reasons and to avoid unneces- sary conformational problems.' *tVibrational spectroscopy' and electron diffraction2' have demonstrated the syn confor- mation of MVE to be the most stable. The second most stable conformer has recently been assigned a quasi-anti con- formation,21 and, on the grounds of molecular orbital (MO) calculations,22 the molecular dipole moment, which is higher in the anti than in the syn conformation by about 1 D, has been considered to be the primary factor determining the syn preference.Procedure and Metbods The geometries of reactants and TSs were determined at dif- ferent levels of theory (AM 1, HF/STO-3G, HF/3-21G, HF/6- 31G*) using the Gaussian 92 program system23 with gradient geometry ~ptimization~~ and default thresholds for con-~ergence.~~The search was limited to concerted TSs, since there is now general agreement that simple 1,3-dipolar cyclo- additions are concerted reactions with no comparable mecha- nistic alternative.16 Up to the HF/3-21G level, critical points were fully characterized by diagonalizing the Hessian matrices calculated for the optimized structures; at the HF/6- 3lG* level, the updated Hessian matrices were diagonalized.TSs were found to have only one negative eigenvalue (first- order saddle points), the corresponding eigenvectors involv- ing the expected concerted formation of the two new bonds.In order to provide a level of confidence in the calculations we made use of different theoretical approximations and decided to rely only on qualitative conclusions shared by all or most of them. The activation barriers were resolved into a number of contributions corresponding to the conceptual steps of the structural and energy changes undergone by the chemical system from the reactant state to the TS. First, isolated reac- tants were deformed to the geometries they assume in the TS (deformation energy). Then the deformed reactants were driven into the overall geometry of the TS, avoiding any elec- tron delocalization between them and, in particular, prevent- ing the formation of new bonds and any through-space delocalization.This model state of localized reaction partners in the TS allows evaluation of the repulsion energy between the deformed reactants. Next, the formation of new bonds was allowed and the delocalization due to the partial forma- tion of the new bonds evaluated. Finally, in a complementary analysis, the role of vicinal delocalizations on the stability of the TSs was evaluated and resolved into a number of additive terms due to single intra- molecular interactions. The operative definitions of energy decomposition and vicinal interaction analysis have been fully described in pre- ceding papers. l0-f t MVE exhibits the same regioselectivity as ethyl vinyl ether; MVE reacted slowly with diazomethane to yield as the only charac- terized and highly dominant adduct 3-methoxy- l-pyrazoline, even if minor amounts of the other regioisomer cannot be ruled out. J.CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Results and Discussion The two regioisomeric TSs will be called A, leading to 4-methoxy-1-pyrazoline and 4-methoxy-2-isoxazoline, and B, leading to 3-methoxy-1-pyrazoline and 5-methoxy-2-isox-azoline (Scheme 1). Tables 1-6 report the main geometrical features of the cal- culated TSs, their activation energies and relative activation energies at different levels of calculation, and analysis of the activation energies and vicinal interactions. The Newman projections along the C-OMe bond (Fig. 1) give a pictorial view of the conformational aspects of the TSs.Tables 1-6 are largely self-explanatory and need not be described in detail; we will limit ourselves to enlarging on only a few points. The first important result is that both A and B TSs exist in two conformations which, in the case of the diazomethane reaction, can be easily related to the syn (Al, B1) and anti (A2, B2) conformations of unreacted MVE ;whereas with for- monitrile oxide, structure A2 shows a clear gauche-like con- formation. Note that, at any level of theory, cycloadditions of both diazomethane and formonitrile oxide are calculated to show the correct regiochemistry (B), and that the lowest- energy TS (B2) is related to the higher-energy anti conforma- tion of MVE. In both cycloadditions, B2 is the most favoured and 'earliest' among the four calculated TSs.This is coher- ently shown (Tables 2 and 5) from its low deformation energy, low repulsion between deformed fragments and low stabilization of the partial new bonds. Furthermore, B2 has the largest incipient bond distances (Tables 1 and 4) and the lowest incipient bond densities (Tables 2 and 5). While such an early TS for the favoured regiochemical approach is hardly consistent with the basic assumption of FMO regio-chemistry theory, which predicts the highest charge-transfer stabilization of the incipient bonds to be favoured, the ration- alization in terms of steric, electrostatic and delocalization interactions explains the regiochemistry itself.The dipole moments of the A1 and B2 TSs are much lower than those of the A2 and B1 TSs (Tables 1 and 4). The approaches A1 and B2 are electrostatically favoured, with respect to A2 and B1, by the relative orientations of the reac- tant dipole moments so that, at a qualitative level, the values in Tables 1 and 4 could easily be anticipated. It follows that electrostatic interactions can enter the product selection only by contributing a conformational preference to B2 over B1 or to A1 over A2, but cannot be a major factor in determining Table 1 Transition structures' of the cycloaddition of methyl vinyl ether to diazomethane (1, HF/3-21G; 2, HF/6-31G*) (a) Structure A1 B1 A2 B2 1 2 1 2 1 2 1 2 ~ 1.367 1.376 1.365 1.373 1.361 1.370 1.359 1.366 2.168 2.139 2.216 2.173 2.212 2.187 2.217 2.170 2.232 2.252 2.21 1 2.254 2.214 2.224 2.246 2.298 102.7 103.0 105.1 106.2 102.8 102.8 104.4 105.7 102.6 101.6 100.2 98.4 102.7 101.9 100.6 98.5 11.9 19.2 19.8 16.0 192.1 190.5 173.7 177.0 141.5 139.0 141.6 139.0 142.4 139.8 142.9 140.3 0.9030 1.0675 3.5796 3.2446 3.3967 3.1421 1.4160 1.1718 (b) Activation energy activation energyd/kcal mol -' A1 B1 A2 B2 AM1 opt 23.4 (3.5) 20.4 (0.5) 24.9 (5.0) 19.9 (0.0) HF/STO-3G opt 25.0 (2.0) 24.7 (1.7) 24.8 (1.8) 23.0 (0.0) HF/3-21G opt 31.1 (0.7) 31.9 (1.5) 32.4 (2.0) 30.4 (0.0) HF/6-31G* opt 39.8 (2.3) 39.9 (2.3) 39.5 (1.9) 37.6 (0.0) HF/6-3 1 G*//HF/3-2 1 G 40.2 (2.2) 40.2 (2.2) 40.0 (2.0) 38.0 (0.0) MP2/6-3 1G*//HF/3-2 1G 12.8 (0.7) 13.7 (1.6) 13.0 (0.9) 12.1 (0.0) MP2/6-31G*//HF/6-31G* 12.2 (1.4) 12.6 (1.8) 12.3 (1.4) 10.8 (0.0) 'Bond lengths in A; angles in degrees; dipole moment, p, in D; energy relative to the B2 structure in parentheses.C-C bond lengths in syn and anti MVE are: 1, 1.316 (syn), 1.312 (anti); 2, 1.320 (syn), 1.316 (anti). 'syn and anti structures of MVE are planar (k0.04")in both calculations. Activation energy with respect to syn MVE; E(anti)-E(syn)/kcal mol-' is: 1, 3.4; 2,2.0. Table 2 Contributions to the activation energy" of the cycloaddition of methyl vinyl ether to diazomethane A1 B1 A2 B2 Ea 23.3 (2.5) 22.4 (1.6) 22.9 (2.2) 20.7 (0.0) EDF 10.5 9.7 10.7 9.2 ED, 19.0 18.0 18.1 16.8 29.5 (3.5) 27.7 (1.7) 28.8 (2.8) 26.0 (0.0)EdeF Etot.rep. 81.5 (8.4) 77.5 (4.4) 77.3 (4.2) 73.1 (0.0) -.82.4 (-10.1) -77.4 (-5.1) -77.6 (-5.3) -72.3 (0.0)deloc.bond density, C-..C 0.5659 0.4907 0.5464 0.4724 bond density, C. * .N 0.5105 0.5561 0.5030 0.5404 'Calculations HF/STO-3G//HF/3-21G; energy in kcal mol-' ; En, activation energy; ED,, deformation energy of the dipolarophile; E,, deformation energy of the 1,3dipole; Edef,total deformation energy; EWt. delocalization energy of the new rep., total repulsion energy; Enbdeloc., bonds. 'Density matrix element, in the orthonormal hybrid basis set, corresponding to the hybrids forming the new bond. J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Table 3 Analysis of vicinal interactions" in the transition structures of the cycloaddition of methyl vinyl ether to diazomethane A1 B1 A2 B2 -33.8 (2.1) -37.8 (-2.0) -31.6 (4.2) -35.8 (0.0)'vie.deloc. new bonds, Olp*x -19.7 -22.6 -18.5 -20.7 new bonds, Olp, new bonds, 0-Me W)-C(2), OIp,x C(l)-C(2), OIp,u C(l)-C(2), 0-Me C(l)-H, OIp,x W-H, OIp,u C(1)-H, 0-Me " Calculations HF/STO-3G//HF/3-21Ga -0.2 -0.7 -0.2 -1.0 -0.2 -0.1 -0.1 -0.3 -0.6 -1.2 -0.5 -0.1 -5.0 -5.2 -1.6 -1.7 -0.3 -0.1 -4.2 -4.7 -0.9 -0.0 -0.9 -2.2 -2.2 -2.5 -5.2 -4.9 -4.7 -5.3 -0.4 -0.2 Table 4 Transition structures' of the cycloaddition of methyl vinyl ether to formonitrile oxide (HF/3-21G) (a)Structure A1 B1 A2 B2 C(l)--C(2)c-..c 1.354 2.181 1.357 2.234 1.351 2.190 1.352 2.222 c-* a 0 2.174 2.305 2.153 2.352 c.* c-c 98.4 103.5 99.4 100.6 0..c-c 106.5 101.2 106.1 103.0 a[MeOC( 1 )C( 2)] C-N-0 13.9 134.6 34.0 137.3 -90.4 135.8 160.9 137.3 c1 2.3792 4.7583 4.1723 2.1934 (b) Activation energy activation energykcal mol ~~ A1 B1 A2 B2 ~~ HF/3-21G opt HF/6-3 1G *//HF/3-2 1 G MP2/6-31G*//HF/3-21G 29.4 (9.1) 41.1 (10.6) 18.0 (1.3) 23.2 (2.8) 34.0 (3.6) 18.9 (2.2) 29.5 (9.2) 41.9 (11.4) 21.5 (4.8) 20.3 (0.0) 30.5 (0.0) 16.6 (0.0) See footnotes of Table 1.Table 5 Contributions to the activation energy" of the cycloaddition of methyl vinyl ether to formonitrile oxide A1 B1 A2 B2 22.1 (1.1) 22.3 (1.3) 22.2 (1.2) 21.0 (0.0)5.6 8.6 9.2 7.1 23.8 20.3 22.4 20.3I.29.4 (1.9) 28.9 (1.5) 31.5 (4.1) 27.4 (0.0)Edcf Eta,.rea. 70.5 (1 7.5) 53.2 (0.2) 69.4 (1 6.4) 53.0(0.0)-71.5 (-20.9) -.53.1 (-2.5) -72.3 (-21.7) -50.6 (0.0)deloc. bond density, C. .C 0.5015 0.3906 0.4979 0.3694 bond density, C. * .O 0.4837 0.4578 0.4939 0.4533 'See footnote of Table 2. Table 6 Analysis of vicinal interactions' in the transition structures of the cycloaddition of methyl vinyl ether to formonitrile oxide A1 B1 A2 B2 'vie. deloc. -33.8 (16.9) -49.8 (1.0) -28.0 (22.7) -50.7 (0.0)new bonds, Olp,= -19.5 -26.7 -0.4 -30.0 new bonds, Olp,~ new bonds, 0-Me C(1)-C(2), OIp,x C(l)-C(2), OIp,uC(l)-C(2), 0-Me C(l)--H, OIp,r C(l)-H, OIp,0 C(l)-H, 0-Me " Calculations HF/STO-3G//HF/3-21G. -0.3 -3.9 -5.0 -2.5 -0.1 -1.4 -6.4 -1.2 -0.8 -3.2 -7.7 -0.9 -5.2 -5.1 +0.1 -1.8 -0.2 0.0 -0.2 -5.2 -0.3 -1.3 -7.3 -2.6 -2.3 -2.4 -1.2 -6.1 -5.0 -5.7 0.0 -0.3 J.CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 tie B1 A2 82 Fig. 1 Schematic view along the O--C(l) bond of the TSs of diazomethane (top) and formonitrile oxide (bottom) with methyl vinyl ether the regiochemistry of MVE cycloaddition. Hence, one can confidently predict that a change in polarity of the reaction medium should not bring about relevant changes in the regiochemical outcome. Steric interactions between the 1,3-dipoles and MVE, as presumed, have no regiochemical role in the examples in question. The conformational features shown in Fig.1 suggest that rotations of the O-Me bond are apparently contrasteric (i.e. the methyl groups occupy ‘inside’ positions in A1 and B1 and ‘outside’ positions in A2 and B2). The only case of non-contrasteric rotation, A2 (methyl group in the anti position), is probably traceable to the electrostatic repul- sions between the positive terminus of the 1,3-dipole and the positive shell of the Me group. The electrostatic origin of the O-Me bond rotation is supported by the findings that (i) O-Me rotation in A2 structures is much greater with for- monitrile oxide, where the CH group is smaller but more positive, than with diazomethane, where the CH, group is larger and less positive, and (ii) O-Me rotation towards the dipole negative terminus in structures B2 is greater with the oxygen of formonitrile oxide than with the nitrogen of diazo- methane. The small O-Me rotations in the syn-like structures A1 and B1, on the other hand, improve the alignment of the incipient bond with the oxygen x lone pair (perpendicular to the O-Me bond in the Newman projections of Fig. 1).These rotations increase the stabilization induced by the interaction of the new bond with the lone pair.Vicinal delocalizations (Tables 3 and 6) appear to be the most interesting and original factors in our explanation of the B regiochemistry of MVE. Vicinal delocalization, as a whole, gives a strong preference to TSs with B regiochemistry. This preference, in turn, is significantly linked to the stabilization brought about by the very strong interactions between the incipient bonds and the oxygen n lone pair, interactions which appear to be much more effective when a C- -Xbond, rather than a C..C bond is the nearest neighbour to the lone pair. According to our findings, an explanation for the regiosel- ectivity of MVE 1,3-dipolar cycloaddition and for the main features of the TSs can be formulated as follows: The four- electron three centre conjugation between the x lone pair (OIpJ and the x bond of the allylic fragment 0-C-C, largely responsible for the rotameric energy profde of MVE,” is differently perturbed by the alternative approaches, A or B, the more favourable perturbation dictat- ing the regiochemistry, a more favourable perturbation of vicinal interactions is also the origin of the earliness of the B TSs, of the consequent weakness of their incipient bond sta- bilization and of the low deformation energy and low repul- sion between the deformed fragments in B TSs.Moreover, electrostatic factors contribute only to the conformational preference of B2 over B1. Note, however, that Tables 3 and 6 also show that vicinal interactions other than those discussed above, although much weaker, can contribute significant differential stability to the different transition structures. An extreme case is represented by structure A2 with formonitrile oxide (Fig. 1 and Table 6) which, owing to its peculiar conformation, is strongly stabil- ized by the interactions of the incipient C..C bond with both the synclinal 0 lone pair of the oxygen atom (O,p,Jand the anticlinal O-Me a-bond.The oxygen x lone pair (Olp,=), in turn, interacts strongly with C(1)-H and c(l)-C(2). It follows that it could be rather unsafe, in general, to ascribe relative stabilities to a single interaction, especially when attempting a rationalization of a wide variety of data. If the hypothesis is correct that product selection might occur well in advance of the transition state, and even before reactant geometries have been significantly perturbed, i.e. at distances where only long-range interactions operate, then it can be maintained that the dipolarophile vicinal interactions, long-range perturbed by the approaching 1,3-dipole, are likely to be the strongest orienting factor.25 We are now trying to extend this explanation to other dipolarophiles and 1,3-dipoles.The B regiospecificity of the acrylonitrile-diazomethane cycloaddition, for example, appears to be due to the favourable perturbation, in the B transition structure, of the strong four-electron four-centre conjungation, whereas the mixture (B : A = 87 : 13) experi- enced by the propene-diazomethane cycloaddition ought to be related to different perturbations of the much weaker hyperconjugative interaction present in pr~pene.~’ We thank MURST and CNR for financial support, and CICAIA (University of Modena) for computer facilities. References 1 (a)A. Rastelli, M. Cocchi and E. Schiatti, J. Chem. Soc., Faraday Trans., 1990, 86, 777; (b) A.Rastelli, M. Cocchi, E. Schiatti, R. Gandolfi and M. Burdisso, J. Chem. Soc., Faraday Trans., 1990, 86, 783; (c) A. Rastelli and M. Cocchi, J. Chem. Soc., Faraday 1082 J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 2 3 4 Trans., 1991, 87, 249; (d) A. Rastelli and M. Bagatti, J. Chem. SOC., Fmaday Trans., 1992, 88, 2451; (e) A. Rastelli, M. Bagatti, A. Ori, R. Gandolfi and M. Burdisso, J. Chem.SOC., Faraday Trans., 1993,89, 29; (f) A. Rastelli, M. Bagatti and R. Gandolfi, J. Chem. SOC., Faraday Trans., 1993,89,3913. N. T. Anh, Top. Curr. Chem., 1980,88,145. A. S. Cieplak, J. Am. Chem. SOC., 1981, 103, 4540; A. S. Cieplak, B. D. Tait and C. R. Johnson, J. Am. Chem. SOC., 1989, 111, 8447. H. Li and W. J. leNoble, Red.Trav. Chim. Pays-Bus, 1992, 111, 199. 15 16 and references therein; (c) R. Gandolfi, G. Tonoletti, A. Rastelli and M. Bagatti, J. Org. Chem., 1993,58,6038. M. Bagatti, A. Ori, A. Rastelli, M. Burdisso and R. Gandolfi, J. Chem. SOC., Perkin Trans. 2, 1992, 1657. (a)R. Huisgen, in Nitrile Oxides and Imines in 1,bDipolar Cyclo-addition in Chemistry, ed. A. Padwa, Wiley-Interscience, New York, 1984, vol. 1, p. 1; (b) P. Caramella and P. Grunanger, ref. 16a, p. 1; (c)G. Bianchi, R. Gandolfi and P. Grunanger, in The Chemistry of Functional Groups, ed. S. Patai, Wiley, New York, 1985; p. 737; (d) K. N. Houk, R. A. Firestone, L. L. Munchau- sen, D. H. Mueller, B. H. Arrison and L. A. Garcia, J. Am. Chem. 5 6 7 8 9 10 11 12 13 K. N. Houk, N. G. Rondan and F. K. Brown, Isr.J. Chem., 1983, 23, 3; K. N. Houk, N. G. Rondan, F. K.Brown, W.L. Jorgensen, J. D. Madura and D. C. Spellmeyer, J. Am. Chem. SOC.,1983,105,5980. S. D. Kahn, C. F. Pau, A. R. Chamberlin and W.J. Hehre, J. Am. Chem. SOC., 1987, 109,650; S. D. Kahn and W. J. Hehre, J. Am. Chem. SOC., 1987,109,663. (a)I. Fleming, Frontier Orbitals and Organic Chemical Reactions, Wiley, Chichester, 1976; (b) p. 153. S. D. Kahn, C. F. Pau, L.E. Overman and W. J. Hehre, J. Am. Chem. SOC., 1986,108,7381. Y. Wu, Y. Li, J. Na and K. N. Houk, J. Org. Chem., 1993, 58, 4625. M. Burdisso, R. Gandolfi, S. Quartieri and A. Rastelli, Tetra-hedron, 1987,43,159. K. N. Houk, in 1,3-Dipolar Cycloaddition Chemistry, ed. A. Padwa, Wiley, New York 1984, vol. 2, p. 442. R. A. Firestone, J. Org.Chem., 1976,41,2212. R. Sustmann, W. Sicking and M. Felderhoff, Tetrahedron, 1990, 46,783. 17 18 19 20 21 22 23 24 25 SOC.,1985, 107, 7227; (e) J. J. W. McDouall, M. A. Robb, U. Niazi, F. Bernardi and H. B. Schlegel, J. Am. Chem. SOC., 1987, 109,4642. F. Marinone Albini, D. Vitali, R. Oberti and P. Caramella, J. Chem. Res., 1980, (S) 348; (M) 4355. R. Gandolfi, unpublished results. N. L. Owen and N. Sheppard, Trans. Faraday SOC., 1964, 60, 634; P. Cahill, L. P. Gold and N. L. Owen, J. Chem. Phys., 1968, 48,1620. N. L. Owen and H. M. Seip, Chem. Phys. Lett., 1968,48, 162. E. Gallinella and B. Cadioli, J. MoZ. Struct., 1991,249,343. D. Bond and P. R. Schleyer, J. Org. Chem., 1990,55,1003. M. J. Frisch, G. W. Trucks, M. Head-Gordon, P. M. W. Gill, M. W. Wong, J. B. Foresman, B. G. Johnson, H. B. Schlegel, M. A. Robb, E. S. Replogie, R. Gomperts, J. L. Andres, K. Raghava-chari, J. S. Binkley, C. Gonzalez, R. L. Martin, D. J. Fox, D. J. Defrees, J. Barker, J. J. P. Stewart and J. A. Pople, Gaussian 92, Gaussian Inc., Pittsburgh PA, 1992. H. B. Schlegel, J. Comput. Chem., 1982,3,214. A. Rastelli, unpublished results. 14 (a) A. Rastelli, M. Burdisso and R. Gandolfi, J. Phys. Org. Chem., 1990, 3, 159; (b) M. Burdisso, A. Gamba, R. Gandolfi, L. Toma, A. Rastelli and E. Schiatti, J. Org. Chem., 1990, 55, 3311, Paper 4/oooO3J; Received 4th January, 1994

ISSN:0956-5000    

DOI:10.1039/FT9949001077

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. CHEM. SOC. FARADAY TRANS., 1994, 90(8), 1083-1088 Excess Volumes of the Ternary Mixtures Butylamine-Cyclohexane- Benzene and Tributylamine-Cyclohexane-Benzene S. L. OswaI* and S. G. Patel Department of Chemistry, South Gujarat University, Swat395 007, India Excess volumes of the ternary mixtures butylamin-yclohexane-benzene and tributylamine-cyclohexane-benzene at 298.15, 303.15 and 313.15 K have been investigated from density measurements using a vibrating densitometer. A number of empirical equations predicting ternary mixture properties from the composite binary parameters have been examined. Furthermore, the Prigogin-Flory-Patterson theory has been extended for ternary mixtures and is applied to the present ternary mixtures. Experimental excess molar volumes, VE, are required when classical thermodynamics is to be used to relate and to compute the equilibrium properties of liquid mixtures.They are of particular importance for both the testing of existing theories and the development of new theories of mixtures. ' Theoretical predictions of VE of non-ideal binary liquid mixtures are more or less satisfactory for determining the sign and approximate magnitude. However, for ternary mix- tures the predictive approach is much more complex and unreliable.2 Rastogi3 has shown that the results of empirical correlations of sets of binary and ternary experimental data may be valuable for interpreting the interactions between the molecules in such systems. A number of researchers2-, have proposed empirical equations to predict excess thermodyna- mic properties for ternary mixtures from the results of corre- sponding binaries.However, experimental measurements of VE for ternary mixtures are scarce, making it difficult to test the predicting ability of these various equations. In a previous paper" we have published VE values of binary mixtures of triethylamine and tributylamine with alkanes and alkylamine at three temperatures. In continua- tion of this work, this paper provides VE values of two ternary mixtures, butylamine(l)-cyclohexane(2)-benzene(3) and tributylamine(l)-cyclohexane(2)-benzene(3) and of the corresponding binary mixtures at 298.15, 303.15 and 313.15 K. The present values of VE for ternary mixtures are com- pared with those obtained from the different empirical expressions due to Redlich-Kister; Tsao-Smith,' Kohler,6 Ja~ob-Fitzner,~ Rastogi et ~l.,~and Lark et aL9 employing the binary mixture data, as well as with those predicted by the Prigogine-Flory-Patterson (PFP) statistical theory.' '-14 Experimental Material Butylamine (C4H,NH2) and tributylamine [(C,H,),N] of Fluka (puriss grade), and cyclohexane (C6HI2) and benzene (C6H6) of BDH (AnalaR grade) were used in this work.C,H,NH2 and (C4H,),N were refluxed over Na and then distilled using a fractionating column.'5 C6H12 and C6H6 were purified by standard procedures as recommended by Riddick et all6 The purities of the liquids were checked by measuring their densities, p, and refractive indices, n,.The values obtained for p and n, are compared with the literature in Table 1. The purities of the liquid (as tested by gas-liquid chromatographic analysis) were better than 99.7 mol% for C6H1, and C6H6 and 99 mol% for C4H,NH2 and (C,H,),N. Thrice-distilled water and dehumidified air were used for densitometer calibration. Mixture Preparation All the mixtures were prepared by mixing weighed amounts of pure liquids in air-tight, narrow-mouth stoppered bottles. A Mettler (AE 163,Switzerland) balance with a precision of 1 x lo-' g was used for the purpose. Proper care was taken to minimize evaporation of the components. Hence, the pos- sible error in the mole fraction is estimated to be lower than +2 x 10-4. Density Measurements The densities of pure liquids, binary mixtures and ternary mixtures were measured with an Anton-Paar model DMA 60/602 vibrating tube densitometer, thermostatted at the desired temperature within f0.01K using a HetoBirkeroad ultrathermoset together with a digital thermometer as described elsewhere." Water and air were chosen as cali- brating fluids, since they span a wide range and their den- sities are known to a high level of precision.'6*21 The precision of p measured is estimated to be better than kO.02 kg m-,.The VE values covering the complete composition range were calculated from the molar masses, M, and the densities, p, of the pure liquids and mixtures. The estimated error in VE for all systems was smaller than +6 x lo-, m3 mol-'.Results and Discussion The experimental VE values at different mole fractions of the four binary mixtures C4H,NH2-C6H, 2, C4H,NH2-C6H6, Table 1 Density and refractive index of pure liquids at 298.15 K densityhg m-liquid exp. lit. C,H,NH, 733.35 733.08" 734.52' (C,H,),N 774.23 773.78" 774.306 C6H12 773.90 773.85f C6H6 873.62 873.6Sf refractive index exp. lit. 1.3977 1.3987b 1.4267 1.4265' 1.4268' 1.4262 1.4253b 1.4978 1.4979' a Ref. 15; 'ref. 16; ref. 17; ref. 18; ref. 19; ref. 20. 1084 J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Table 2 Excess molar volume, VE, for binary mixtures at 298.15, (C4Hg)3N<,H12 and (C,Hg)3N-C,H, at 298.15, 303.15 and 303.15 and 313.15 K 313.15 K are reported in Table 2.A variable-degree polynomial of the form X1 298.15 303.15 313.15 C4H9NH&6H 12 0.1098 0.428 0.435 0.445 was fitted to each binary mixture at each temperature by the 0.1980 0.657 0.668 0.684 0.3883 0.847 0.876 0.889 least-squares method. 0.4834 0.837 0.859 0.877 The parameters A,, of eqn. (1) and the standard deviations, 0.5922 0.757 0.77 1 0.797 a,? are given in Table 3. Table 3 also lists the required 0.8112 0.454 0.464 0.488 parameters, A,, of eqn. (1) for the binary mixture 0.8919 0.273 0.282 0.290 cyclohexane-benzene at 298.15, 303.15 and 313.15 K, taken from the literature.20.22 C4H9NH 246H6 0.0974 0.059 0.050 0.042 Fig. 1 and 2 show VEplotted against x1 for the first com- 0.1974 0.128 0.122 0.08 1 ponent and the VE curves calculated from the smoothing 0.3596 0.226 0.22 1 0.224 equations.0.4787 0.25 1 0.255 0.264 VE values for C,H9NH,-C,H12, C,HgNH2-C,H6,0.5902 0.269 0.270 0.273 0.7984 0.2 13 0.205 0.202 (C,H,),N-C,H,, and (C4Hg),N-C6H, at 298.15 K have 0.9042 0.137 0.132 0.127 been measured earlier.15*23.24 Our results on VE for equi- molar mixtures of these systems are within 5% of the liter- (C4H9)3N-C6H120.1012 0.185 0.183 0.182 ature values, except for the value for (C,H9)3N-C,H12 0.2089 0.283 0.275 0.272 reported by Phuong-Nguyen et aL2, For the latter mixture, 0.4001 0.311 0.302 0.283 VE at xi = 0.5 reported by Phuong-Nguyen et al. is 0.5116 0.277 0.265 0.263 0.389 x lop6 m3 mol-', while Letcher" reports0.5868 0.254 0.245 0.224 0.280 x lo-, m3 mol-'.Our VE value of 0.284 x lo-, m3 0.7953 0.152 0.138 0.124 mol-is very close to that of Letcher.0.9021 0.086 0.073 0.067 Inspection of Table 2 and Fig. 1 and 2 shows that VEfor (c4H9)3N-C gH 6 all the mixtures is positive. VE for C,~gNH,-C,Hl, and 0.1084 0.338 0.348 0.361 (C,Hg)3N-C,H, increases with rise in temperature, while the 0.2016 0.496 0.51 1 0.532 0.2272 0.516 0.540 0.560 0.3639 0.584 0.622 0.647 0.4013 0.573 0.593 0.634 t 6 is defined as 0.4593 0.580 0.608 0.4986 0.544 0.574 0.605 0.6007 0.496 0.53 1 0.565 0.7001 0.414 0.463 0.498 0.7956 0.328 0.373 0.408 0.9003 0.186 0.228 0.250 where n and m,respectively, are number of experimental points and number of coefficients used in eqn. (1). Table 3 Parameters, A,, of the smoothing equation [eqn.(l)] and standard deviations, 6,along with HE (exp), X,,,, and Xi,YE for the equimolar mixture T/K Ad A1 A2 a A3 6' Ht/J mol-' Xij, '/J cm- Xi,yEc/J cm-j C4H9NH2-C6H12 298.15 3.31 15 0.9095 0.6480 0.0065 303.15 3.3969 0.9062 0.6366 0.01 13 1 131d 60.7 50.4 313.15 3.4822 0.8900 0.6781 0.0070 298.15 1.0417 -0.5O44 0.1 147 0.0109 C4H gNH 2-C6H 6 303.15 1.0500 -0.5200 -0.01 82 0.0109 584' 32.5 20.3 313.15 1.0787 -0.5337 -0.1725 0.01 20 298.15 1.1342 0.6670 0.5751 (C4H9)3N-C6H120.0025 303.15 1.0939 0.6526 0.5044 0.0045 151' 5.2 4.9 313.15 1.0357 0.7678 0.5297 0.0059 298.15 2.1874 0.9001 0.9692 (C,H,),N-C,H,0.0043 303.15 2.2889 0.7103 1.263 1 0.0034 775 27.0 13.8 313.15 2.4383 0.6526 1.3246 0.0086 298.15 2.6164 -0.1030 0.0272 0.0010 C6H12-C6H6B 303.15 2.6273 -0.1027 0.0465 0.0017 0.0003 8008 40.6 39.3 313.15 2.6487 0.1086 0.0566 0.0037- 'Units: lo6m3 mol-'.Obtained from HE(exp). Obtained from VE(exp). Ref. 27. Ref. 24. Ref. 28. Ref. 20 and 22. * Ref. 29. J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 u.I 0.6 0.5 r I-0 0.4 E (DI 0.3 1 L 0.2 0.1 0.0 0.0 0.2 0.4 0.6 0.8 1.o XI Fig. 2 Excess volumes for (a) (C,H,),N-C,H,, and (b) (C,H,),N-C,H, at 298.15 (O), 303.15 (A) and 313.15 K (0).Solid curves represent eqn. (1). XI Fig. 1 Excess volumes for (a) C,H,NH2-C,H,, and (b) Solid (C,H,),N-C6H,,-C,H6 and at 298.15, 303.15 and 313.15 KC,H,NH,-C,H, at 298.15 (O),303.15 (A) and 313.15 K (0).curves represent eqn. (1). are presented in Tables 4 and 5. reverse is the case for (C,H,),N-C,H,, . The variation of VE Correlation of VfZ3 with Empirical Equations with temperature for C,H,NH,-benzene is very small and no If the interactions in a ternary i-j-k mixture are assumed to definite trend is observed. The different magnitudes of posi- be closely dependent on the interactions in the constituent tive VE suggest that the effects of size, shape and chemical i-j, j-k and i-k mixtures, it should be possible to evaluate nature of the molecules involved predominate. thermodynamic excess molar volumes for a ternary mixture The experimental excess molar volumes, Vf.,,,for the of non-electrolytes, when the corresponding volumes for ternary mixtures C,H,NH,-C6H,,-C,H6 and binary i-j,j-k and i-k mixtures are known.Table 4 Excess molar volumes, VE, for C,H,NH2 (x,)<,H12 (x,)<,H, (x3) at 298.15, 303.15 and 313.15 K, along with VFFp at 303.15 K; ijVE = VE -VEPFP VE/lO-, m3 mol-' 0.1231 0.2230 0.517 0.524 0.529 0.690 -0.166 0.573 -0.049 0.2509 0.1903 0.556 0.560 0.570 0.792 -0.232 0.601 -0.041 0.3834 0.1577 0.545 0.556 0.572 0.819 -0.263 0.587 -0.03 1 0.5154 0.1231 0.492 0.502 0.533 0.767 -0.265 0.531 -0.029 0.6501 0.0889 0.395 0.396 0.433 0.641 -0.245 0.432 -0.036 0.7842 0.0548 0.302 0.312 0.324 0.446 -0.112 0.295 0.017 0.9252 0.0190 0.141 0.148 0.158 0.171 -0.023 0.111 0.037 0.1218 0.4347 0.745 0.748 0.754 0.898 -0.150 0.770 -0.022 0.2640 0.3687 0.773 0.822 0.847 1.002 -0.180 0.8 15 0.007 0.3931 0.3039 0.767 0.792 0.875 1.013 -0.221 0.792 0.000 0.6642 0.1682 0.542 0.534 0.576 0.759 -0.225 0.568 -0.034 0.8444 0.0772 0.303 0.325 0.345 0.406 -0.083 0.300 0.025 0.9280 0.0360 0.152 0.160 0.174 0.198 -0.038 0.145 0.015 0.1350 0.6479 0.714 0.720 0.738 0.836 -0.055 0.728 -0.008 0.2716 0.5455 0.834 0.849 0.857 1.024 -0.175 0.854 -0.005 0.4065 0.4445 0.830 0.848 0.893 1.082 -0.234 0.882 -0.034 0.5399 0.3446 0.747 0.788 0.836 1.020 -0.232 0.820 -0.032 0.6694 0.2476 0.619 0.631 0.684 0.851 -0.220 0.677 -0.046 0.8004 0.1495 0.404 0.415 0.467 0.580 -0.165 0.460 -0.045 0.9225 0.0580 0.185 0.188 0.195 0.247 -0.059 0.195 -0.007 0.2457 0.3491 0.727 0.743 0.792 0.974 -0.232 0.792 -0.049 0.2461 0.2347 0.625 0.634 0.674 0.854 -0.220 0.667 -0.033 0.1556 0.2285 0.568 0.570 0.577 0.744 -0.174 0.605 -0.035 0.1685 0.6769 0.693 0.707 0.742 0.842 -0.135 0.722 -0.015 0.3139 0.0883 0.420 0.430 0.476 0.652 -0.222 0.436 -0.006 Xijis obtained from equimolar HE(exp). * Xijis obtained from equimolar VE(exp).1086 J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Table 5 Excess molar volumes, VE, for (C4HJ3N (xl)+Hl, (x,)-C6H6 (x3) at 298.15, 303.15 and 313.15 K, along with VFFp at 303.15 K; 6VE = VE -VEPFP ~~ ~ 0.0272 0.2430 0.537 0.538 0.540 0.595 -0.057 0.542 -0.004 0.0676 0.2279 0.610 0.629 0.640 0.734 -0.105 0.614 0.01 5 0.2521 0.1868 0.682 0.695 0.719 0.910 -0.216 0.692 0.003 0.3648 0.1586 0.644 0.664 0.695 0.909 -0.246 0.672 -0.008 0.5110 0.1221 0.523 0.543 0.565 0.808 -0.265 0.584 -0.041 0.7022 0.0744 0.370 0.369 0.382 0.556 -0.187 0.398 -0.029 0.0578 0.4795 0.680 0.706 0.720 0.769 -0.061 0.700 0.006 0.1213 0.4004 0.695 0.711 0.751 0.840 -0.129 0.698 0.013 0.3154 0.3484 0.652 0.675 0.700 0.8 18 -0.143 0.659 0.016 0.4478 0.2810 0.572 0.580 0.588 0.734 -0.154 0.576 0.004 0.6103 0.1983 0.420 0.431 0.436 0.567 -0.137 0.437 -0.006 0.8375 0.0827 0.203 0.201 0.258 0.259 -0.058 0.195 -0.006 0.0649 0.701 1 0.552 0.572 0.568 0.580 -0.008 0.537 0.035 0.1334 0.6497 0.573 0.596 0.614 0.615 -0.019 0.552 0.044 0.2242 0.5816 0.565 0.587 0.599 0.623 -0.041 0.549 0.038 0.2744 0.5440 0.554 0.577 0.588 0.623 -0.016 0.538 0.039 0.0522 0.4778 0.685 0.678 0.674 0.765 -0.087 0.699 -0.021 0.1185 0.4445 0.673 0.702 0.711 0.818 -0.116 0.710 -0.008 0.5178 0.2072 0.486 0.489 0.557 0.718 -0.229 0.543 -0.054 0.4744 0.1241 0.602 0.610 0.626 0.849 -0.239 0.614 -0.004 0.4860 0.4101 0.385 0.389 0.433 0.485 -0.095 0.414 -0.025 X, is obtained from equimolar HE(exp); X, is obtained from equimolar VE(exp).The proposed Redlich and Kister expression4 for the Rastogi et id.* suggested a slightly different equation for excess Gibbs energy of ternary mixtures takes the form for estimating the excess molar volume of a ternary mixture predicting excess molar volumes : ~723= ~7 +2 ~!3+ ~73 (2) in which VF2, V:3 and VY3 represent the excess molar volumes, with xl, x2 and x3 the mole fractions of the ternary mixture calculated with eqn.(1) using the coefficients of Table where the values of Vt for binary mixtures are obtained in a 3. similar manner as for eqn. (4). The Tsao and Smith equation5 for predicting the excess The Jacob-Fitzner equation' is based on the binary data enthalpy of ternary mixtures takes the following form: at the composition nearest to the ternary composition, taking the form for the excess molar volume: where VE refer to the excess molar volumes for the binary mixtures at compositions xo, xy such that xp = xi for the 1-2 x1x3 v?3and 1-3 binary mixtures and x: = x2/(x2 + x3) for the 2-3 binary mixture.(xl + x2/2xx3 + x2/2) The Kohler equation6 for a ternary mixture is of the form: x2x3 v;3(x2 + x1/2xx3 + xl/2) (6) In this equation, VE refers to the excess molar volumes for the binary mixtures at compositions xo and xy, such that where V; is the excess molar volume of the binary mixtures x; = 1 -xj" = Xi/(Xi + Xi). at composition xp ,xy ,such that xi -xj = xo -xy . Table 6 Standard deviations between experimental VE and those obtained from the empirical equations [eqn. (2)-(7)] and PFP theory standard deviation T/K eqn. (2) eqn. (3) eqn-(4) eqn. (5) eqn. (6) eqn. (7) PFP theory butylamine-cyclohexane-benzene 298.15 0.023 0.126 0.029 0.161 0.023 0.104 303.15 0.023 0.120 0.027 0.170 0.023 0.112 0.187" 0.025b 313.15 0.025 0.104 0.028 0.190 0.025 0.128 tributylamine-cyclohexane-benzene 298.15 0.025 0.164 0.035 0.165 0.025 0.093 303.15 0.033 0.163 0.040 0.169 0.035 0.101 0.124" 0.02 1 313.15 0.029 0.154 0.034 0.180 0.029 0.112 " X, adjusted to equimolar HE(exp)ij.X, adjusted to equimolar VE(exp)ij. J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 The equation proposed by Lark et a/.' for estimating the excess molar volumes for ternary mixtures is of the form -k [(n2)23 + (n3)231V;3 + [(%)i3 + (ni)i3lV?3 (7) where (ni)ii is the number of moles of component i in the binary mixture ij such that (r~,),~+ (n1)13 = xl, and x1 dis-tributes itself proportionally between components 1 and 2, i.e.and In order to compare the correlating ability of eqn. (2)-(7), the standard deviations, uybetween the experimental and pre- dicted VE for the ternary mixtures, have been calculated and are recorded in Table 6. Examination of Table 6 shows that eqn. (2), (4) and (6) due to Redlich-Kister, Kohler and Jacob-Fitzner gave similar values of u, while comparatively higher values of ts were obtained with the Rastogi et a!. Lark et al. and TsacAmith equations, the highest being for eqn. (5) of Rastogi et al.' Prigogine-Flory-Patterson Theory The statistical approach of PFP theory h as been 10-14925926 applied successfully to the excess thermodynamic properties of binary liquid mixtures.Here, an attempt is made to extend it to predicting the excess molar volumes of ternary mixtures. By analogy with binary rnixtures,l2 the excess volume for a ternary or higher component mixture is given by VFFp= V* V-1$iq) (8)(-i,j.k where Pand are the reduced volumes of the mixture and of the pure component i, and I/* is the characteristic volume of the mixture. The reduced volume, is related to the reduced temperature T T = ~p-= (PIP -1)/p4/3 (9)1 where T* is the characteristic temperature. The charactersitic volume, V*, temperature, T*, pressure, P*, and energy, U*, for a mixture can be calculated from the values of Flory's characteristic parameters of pure com-ponents applying the following combining rules' 2-'4 with the assumption that two-body interactions are predominant.V* = 1xi Vf (13)i,yk In eqn. (1l), Xijrepresents Flory's contact interaction energy parameter for the ij pair,12 which can be evaluated for each pair ij, jk and ik using either the experimental excess molar enthalpy, HE(exp), or the excess molar volume, VE(exp), of the corresponding pair. 1087 The relation used for Xij:HEfor the ij pair from the excess molar enthalpy, HE(exp)ij, in the notation of Patterson and Delmas14 is, (14) where the free-volume contribution to the excess enthalpy for the ij pair, Hf",ii, is estimated oia HF ij = UtCp,i,(Tu) -T",ij] (15)ci, j for the ij pair using the excess molar volume can be Xi,derived from26 where the free-volume and P* contributions to the excess molar volume for the ij pair are obtained by26 x {$i $j + ($i -djI21 (17) VE(P*)= Vz(q -QO(i-$j) (18) oycpand Tz are reduced quantities and can be evaluated from the appropriate relations with knowledge of c.Fur-thermore, &, Oi and $i, the segment fraction, surface fraction and contact energy fraction, respectively, for component i in the mixture are given by (19) i, j, k Bi = XiSiVf/ I 1xisiVf i. i,k $i = xiPi*Vf/ 1xiP? Vf (21) i, j, k here Si is the molecular surface-to-volume ratio of compone_nt i. Thus, from knowledge of the pure component values of Vf and Pf and the experimental values of either HE or VE for each pair ij, jk and ik,one can evaluate for the ternary mixture through the mixture P* and T*, using eqn.(10)-(18). This enables the excess molar volume for the ternary mixture to be estimated from eqn. (8). In the present work we have determined Xij,HEfrom the equimolar HE(exp)ij value, as well as Xii,VEfrom the equi- molar VE(exp)ii. Both of these values of Xijwere used to esti- mate the excess molar volume for the present ternary mixtures. The values of Flory's parameters for the pure components used are listed in Table 7, while Table 3 includes the values of equimolar HE(exp)ii, Xi,HE and Xij,YE for the composite binary mixtures. The VFFp values at 303.15 K obtained from Xij derived by using equimolar HE(exp) as well as VE(exp) are included in Tables 4 and 5 for comparison with the experimental VE. The difference 6VE (= VFxp-VFFp) at each composition is also given in Tables 4 and 5.The overall standard deviations, 0, between the experimental and theoretical VE for both approaches are included in Table 6. Inspection of Tables 4 and 5 shows that PFP theory always predicts the correct sign for VE at each composition for both ternary mixtures. The values for 6VE are in the range (-0.041 to -0.266) x m3 mol-', when VFFp is J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Table 7 Physical properties and Flory's parameters of the pure components component 0r/10-~K-' V V*/cm3mol-' C,/J K-' mol-'P*/J cmP3 T */K S/A -' cyclohexane 1.23 3 1.2975 84.33 benzene 1.233 1.2975 69.33 533 4730 0.93 158.1 623 4730 1.oo 136.8 but ylamine 1.319 1.3137 76.43 582 459 1 1.14 190.7 tributylamine 0.990 1.2491 192.35 448 5299 0.88 374.0 obtained from X, HE.On the other hand, when VFFpis calcu- lated using Xij,YE,6VE lies in the narrow range (-0.054 to 0.044) x m3 mol-l. Similarly, the overall standard devi- ations, 0, at 303.15 K are (0.187& 0.077) x m3 mol-' 7 8 9 K. T. Jacob and K. Fitzner, Thermochim. Acta, 1977,18, 197. R. P. Rastogi, J. Nath and S. S. Das, J. Chem. Eng. Data, 1977, 22, 249. €3. Lark, S. Kaur and S. Singh, Indian J. Chem. Sect. A, 1981,26, 197. and (0.124f0.080) x m3 mol-l, for C,H,NH,- 10 S. G. Pate1 and S. L. Oswal, J. Chem. SOC.,Faraday Trans., 1992, when HE(exp) is used to derive Xij, but they are only (0.025 f0.014) x m3 mol-' and (0.021 0.015) x m3 mol-', respectively, when X, is adjusted to the binary VE(exp) data.It may be concluded that the estimated V;,, values for the ternary mixture investigated are quite satisfactory when X, is adjusted to binary VE(exp) data, and are much better than those predicted using Xi.obtained through HE(exp). Further- VE(exp) data are also as good as those predicted by the empirical equations [eqn. (2), (4) and (6)], which also use C6H 12-C6H6 and (C,H,),N-C,H 1,-C,H,, respectively, more, the theoretical V,,,b values estimated through binary 11 12 13 14 15 16 17 18 19 88,2497. I. Prigogine, The Molecular Theory of Solutions, North Holland, Amsterdam, 1957. P. J. Flory, J. Am. Chem. SOC., 1965,87, 1833. A. Abe and P. J. Flory, J. Am. Chem. SOC., 1965,87, 1838. D. Patterson and G. Delmas, Discuss.Faraday SOC., 1970,49,98. T. M. Letcher, J. Chem. Thermodyn., 1972,4, 159; 551. J. A. Riddick, W. B. Bunger and T. K. Sakano, Organic Solvents: Physical Properties and Methods of Purijication, Wiley Inter- science, New York, 4th edn., 1986. A. Krisnaiah and P. R. Naidu, J. Pure Appl. Ultrason., 1987,9,2. C. Klofutar, S. Paljk and D. Krenser, J. Znorg. Nucl. Chem., 1975,37,1729. R. Philippe, G. Delmas and M. Couchen, Can. J. Chem., 1978, VE(exp) of the composite binary mixtures. 20 56,370. K. Tamura, K. Ohomuro and S. Murakami, J. Chem. Thm- One of us (S.G.P.) wishes to acknowledge the Government of Gujarat for the award of a research fellowship during the course of this work. 21 22 modyn., 1983, 15, 859. Handbook of Chemistry and Physics, ed. R. C. Weast, CRC Press, Boca Raton, 59th edn., 1979. K. Tamura and S. Murakami, J. Chem. Thermodyn., 1984, 16, 33. 23 T. M. Letcher and J. W. Bayles, J. Chem. Eng. Data, 1971, 16, References 24 266. H. Phuong-Nguyen, €3. Riedl and G. Delmas, Can. J. Chem., 1 J. S. Rowlinson and F. L. Swinton, Liquids and Liquid Mixtures, Butterworth, London, 3rd edn., 1982. 2 G. L. Bertrand, W. E. Acree Jr. and T. E. Burchfield, J. Solution Chem., 1983,12,327. 3 R. P. Rastogi, J. Sci. Znd. Res., 1880,39,480. 4 0.Redlich and A. T. Kister, Znd. Eng. Chem., 1948,40,345. 5 C. S. Tsao and J. M. Smith, Chem. Eng. Prog. Symp. Ser., No. 7, 25 26 27 28 29 1983,61,1885. M. Costas and D. Patterson, J. Solution Chem., 1982,11, 807. B. Riedl and G. Delmas, Can. J. Chem., 1983,61,1876. J. Fernandez, I. Velasco and S. Otin, Znt. Data Ser., Sel. Data Mixtures, Ser. A(3),1990, 166; 167. A. S. Kertes and F. Grauer, J. Phys. Chem., 1973,77,3107. K. Elliot and C. J. Wormald, J. Chem. Thermodyn., 1976,8,881. 1953, 49, 107. 6 F. Kohler, Monatsh. Chem., 1960,91,738. Paper 3/06573A; Received 3rd November, 1993

ISSN:0956-5000    

DOI:10.1039/FT9949001083

出版商:RSC    

年代:1994

数据来源: RSC