摘要:

AbstractFluorescence excitation spectra of CH3CH2CH2O (n‐propoxy) and (CH3)2CHO (i‐propoxy) radicals were obtained using a combined laser photolysis/laser‐induced fluorescence (LIF) technique and the kinetics of reactions of these radicals with (1) O2as a function of temperature and with (2) NO2as a function of pressure have been determined.Propoxy radicals were produced by excimer laser photolysis of the appropriate propyl nitrites at λ = 351 nm. The spectra of the (Ã←X̃) transitions show progressions of the CO‐stretching vibration in the electronically excited states with spacings of the bands of (560±10) cm−1fori‐propoxy and (580±10) cm−1forn‐propoxy. Fluorescence spectra taken after excitation in the (4,0) band at λ = 340.1 nm (i‐propoxy) and in the (1,0) band at λ = 342.4nm (n‐propoxy) show progressions of the CO‐stretching vibration in the electronic ground state of (900±60) cm−1fori‐propoxy and (1000±50) cm−1forn‐propoxy.The Arrhenius expressions for the ractions ofn‐propoxy andi‐propoxy with O2have been determined to bek1(n) = (1.4±0.6)×10−14exp (0.9±0.5) kJ mol−1/RT) cm3s−1andk1(i) = (1.0±0.3)×10−14exp (‐(1.8±0.4) kJ mol−1/RT) cm3s−1in me range 218–313 K. The rate coefficients for the reactions of NO2withn‐propoxy andi‐propoxy atT= 296 K were found to be independent of total pressure withk2(n) = (3.6±0.4

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020502

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractLaser induced fluorescence (LIF) from the (2,0) and (3,0) band of the A2∏3/2← X2∏3/2transition of IO was detected. Using this detection, the rate constants for the reactions (1) I+O3→ IO+O2, (2) O(3P)+I2→ IO+I, (3) O(3P)+CH3I → IO+CH3and (4) O(3P)+CF3I → IO+CF3were determined. Reactions (1), (3) and (4) were investigated over me temperature range 230 to 310 K, whereas reaction (2) was measured only at 295 K. The rate constants for these reactions can be described by the following Arrhenius expressions:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {k_1 (T) = (1.6 \pm 1.2) \cdot 10^{ - 11} \cdot \exp \left({- \frac{{(750 \pm 194)}} {T}} \right)\;{{\rm cm}}^3 \;{{\rm molecule}}^{ - 1} {{\rm s}}^{ - 1} } \\ {k_2 (295\;{{\rm K}}) = (1.3 \pm 0.15) \cdot 10^{ - 10} \;{{\rm cm}}^3 \;{{\rm molecule}}^{ - 1} \;{{\rm s}}^{ - 1} } \\ {k_3 (T) = (6.2 \pm 1) \cdot 10^{ - 12} \cdot \exp \left({\frac{{(341 \pm 37){{\rm K}}}} {T}} \right)\;{{\rm cm}}^3 \;{{\rm molecule}}^{ - 1} \;{{\rm s}}^{ - 1} } \\ {k_4 (T) = (1.3 \pm 0.5) \cdot 10^{ - 11} \cdot \exp \left({\frac{{(266 \pm 85){{\rm K}}}} {T}} \right)\;{{\rm cm}}^3 \;{{\rm molecule}}^{ - 1} {{\rm s}} - 1} \\ \end{array} $$

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020503

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe phosphate ester 1,1′‐binaphthyl‐2,2′‐diyl‐phosphate shows an intense fluorescence of the binaphthyl moiety. In the complex 1,1′‐binaphthyl‐2,2′‐diyl‐phosphato‐pentaammine‐cobalt(III) this emission is quenched by excited state electron transfer to Co(III). As a consequence the phosphate ester undergoes an oxidative cleavage while Co(III) is reduced to Co(II) with ϕ

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020504

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe photophysical and photochemical properties oftrans‐R‐2′,4′‐dinitrostilbene (II) and a series oftrans‐R‐2′,4′‐dinitrostilbenes (II‐R, R: 2‐NO2, 3‐NO2, 4‐Br, 4‐F, 4‐Me, 4‐C3H7, 4‐OCH2C6H5, 3,4,5‐(OMe)3, 4‐OEt, 4‐NMe2, 4‐NEt2) were studied in solution as a function of solvent polarity and temperature. The quantum yield of fluorescence (Φf) is very small for allII‐R at 25°C. At −196°C Φfis moderate for several derivatives in 2‐methyltetrahydrofuran (MTHF) but strongly enhanced for those bearing electron donating substituents. For the latter compounds the quantum yield oftrans→cisphotoisomerization is low, but for the other compounds Φt → cis substantial (0.2‐0.5 in toluene or MTHF at room temperature). The triplet state absorbs typically in a broad spectral range; its lifetime (τT) lies in the 20‐200 ns range and is longer for R = 4‐NEt2; at −196°C τTof allII‐R approaches milliseconds. The results are compared with those oftrans‐4‐R‐4′‐nitrostilbenes (I‐R, R: NO2, H, OMe, NH2, NMe2, NEt2). Phosphorescence of singlet molecular oxygen was observed for several mono‐ and dinitrostilbenes at room temperature. Generally, the quantum yield of singlet oxygen formation is much smaller than that of intersystem crossing into the triplet state. The triplet mechanism accounts fortrans→cisphotoisomerization and the contribution of this pathway is lowered by intramolecular electron transfer to the nitro group(s). The similarities and differences betweenI

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020505

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe spectral shift of absorption and fluorescence bands as well as the fluorescence decay of four J‐aggregate forming 5,5′,6,6′‐tetrachlorobenzimidacarbocyanine dyes have been investigated in solution under high pressure up to 50 kbar0 The investigated dyes differ only in their 1,1′ and 3,3′ nitrogen substituents which do not influence the chromophore itself. Whereas the spectral behaviour of the monomeric dyes is comparable to that of aromatic and polyenic compounds, the J‐aggregates show some unusual spectral features.Two types of J‐aggregates can be distinguished. One type exhibits a linear dependence of the absorption and fluorescence maximum on pressure wim vanishing Stokes shift over the whole pressure range. The second type is characterised by a limited shift of the absorption band to longer wavelengths whereas the Stokes shift increases even at pressures where the absorption energy remains constant.The spectral behaviour of the first type is consistent with the well‐known chain‐shaped or brickstone‐like structure of J‐aggregates. As one dye of the second type is known to form optically active, Davydov‐split J‐aggregates the pressure‐dependent spectral behaviour of such dyes corroborates the assumption mat their J‐aggregates consist

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020506

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractA new optical high pressure cell was developed, which allows to induce pressure jumps within τ ≈︁ 0.5 ms and τ ≈︁ 50 ms and with an amplitude up to |ΔP| ≈︁ 6 MPa. With this cell the transmitted and scattered light intensities at fixed angles (θ = 20°, 50°, 80°, 110°, 140°) can be measured simultaneously as a function of time, e.g. at the phase transition isotropic‐nematic of a selected liquid crystal (here trans‐4‐n‐pentyl(4‐cyanophenyl)‐cyclohexane, PCH 5). The temperature changes during the pressure jumps are also registrated. TheT(p) phase diagram of the liquid crystal is known from DSC measurements. Simultaneous time‐dependent measurements of transmitted and scattered light intensities allow a discussion of the processes that occur at the transition. The treatment of these processes has been approached accord

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020507

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractMonolayers of the methyl‐branched phospholipid l‐(2‐methylstearoyl)‐2‐hexadecylphosphatidylethanolamine (1) at the air/water interface and in contact with hexadecane are studied by pressure‐area isotherm measurements and grazing incidence x‐ray diffraction (GKD). The monolayers exhibit at both interfaces two diffraction peaks indicating a rectangular unit cell with next‐nearest neighbor (NNN) tilt at 20°C and at all lateral pressures investigated. Compared to the double‐chain DPPE, the introduction of the medryl side group changes the tilt direction from nearest neighbour (NN) to NNN, increases me tilt angle drastically and prevents the transition to the untilted hexagonal phase. The hexadecane contact decreases the tilt angle of (1) which shows that hexadecane is incorporated into the monolayer. However, the tilt angle can be reduced only to 13°. Comparison of the isotherm with the molecular areas determined by GIXD indicates that the monolayer consists of ordered and non‐ordered parts, the latter of which do not contribute to th

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020508

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe anodic dissolution of silver at the solid‐solid interface Ag|α‐AgI has been studied by means of a high precision (capacitive) dilatometer. The dilatometer signal corresponds to the change of the anode thickness during the dissolution experiment. Under galvanostatic conditions and in a definite pressure range the dilatometer signal oscillates periodically, i.e., me length change of the anode with time is not a simple and linear function of the current density. The mean length change is, as expected, proportional to the electric current. The oscillation modes of the dilatometer signal are correlated with simultaneous electrochemical oscillations at the anode and give evidence for the influence of morphological effects on the interface kinetics. From the combination of both electrochemical and dilatometric (mechanical) experiments, we draw conclusions on a possible mechanism of the observed oscillatory kine

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020509

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractPowder X‐ray diffraction and cryo electron diffraction techniques supported by computer simulations were used to determine the secondary structures of the series of heteropoly acid (HPA) compounds CsxH4‐xPVMo11O40·nH2O (0≤x≤4). The structures of the caesium salts (2≤x≤4) are simple cubic with space group Pn3m. The free acid exhibits a triclinic lattice (P−1) for the majority of all crystals. A small fraction of thin crystals was detected with simple cubic structure (Pn3m). Computer simulations of the X‐ray diffraction patterns suggested that the structure of Cs2H2PVMo11O40·5H2O contains defects in the cation lattice. The caesium ion occupancy is 2/3. [H5O2]+‐groups occupy 1/3 of the cation positions. The diffraction pattern of Cs4PVMo11O40·5H2O could be simulated when only 3/4 of the anion positions are occupied. Cs3HPVMo11O40·7H2O crystallises in a simple cubic lattice without any defects.The secondary structures of the investigated heteropoly salts can, therefore, be described by a single structure with variable site occupations, with the exception of Cs3HPVMo11O40·7H2O (caesium ion occupancy of 1 and poly anion occupancy of 1). All salts belong to one phase with large stoichiometric variations. A mixture of acid and caesium salt, with the acid epitactly grown on the salts, an intergrowth‐structure witii varying caesium ion content, mixed crystals as well as the coexistence of a nanocrystalline X‐ray‐invisible form of free acid besides caesium salt could be excluded for the partly neutralised materials. Selected physico‐chemical properties of the HPA compounds, which depend on the caesium ion content, will be rationalised widi the knowled

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020510

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe ‘Simulated Annealing’ algorithm is used to analyse Mössbauer spectra with distributed hyperfine structure parameters. The distribution is described by a set of points. No initial assumptions regarding the distribution function are therefore necessary to run the program successfully. The algorithm can be easily extended to handle more than one distribu

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020511

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY