摘要:

AbstractThe Raman (1800–10 cm−1) and infrared (2000–30 cm−1) spectra of bromodifluoroacetyl chloride, CBrF2CClO, are reported for the gas and polycrystalline solid. Additionally, the Raman spectrum of the liquid along with qualitative depolarization ratios have also been obtained. These data have been interpreted on the basis of an equilibrium between thegaucheand thetransconformers (bromine atomtransto the chlorine atom) in the gas and liquid phases. From a study of the Raman spectrum of the liquid at various temperatures, a value of 851 ± 56 cm−1(2.43 ± 0.07 kcal mol−1) was obtained for ΔHwith thegaucheconformer the more stable form. A similar study of the gas gave a value of 725 ± 150 cm−1(2.07 ± 0.43 kcal mol−1), again with thegaucherotamer the more stable conformer. Hence thegaucheconformer is the predominate rotamer in the gas and liquid and the only conformer present in the annealed solid. Aided byab initioand scaled computations of the vibrational spectrum with the STO‐3G* basis set and, for thetransconformer at the 4–31G*/MIDI‐4* level of the theory, complete assignments of observed bands to fundamental vibrations of thegaucheconformer are made, whereas partial assignment is reported for thetransconformer. The fundamental torsional mode for thegaucheconformer was observed at 46 cm−1but excited‐state transitions were not observed so the potential function governing the conformational interchange could not be determined. Optimized geometries, dipole moments, unscaled and scaled vibrational frequencies and harmonic force fields are reported for both conformers. With the STO‐3G*, basis set, thegaucheconformer is calculated to be more stable than thetransconformer by 17 cm−1(48 cal mole−1). These results are compared with the corresponding q

ISSN:0377-0486    

DOI:10.1002/jrs.1250240102

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractSulphur vapour was investigated by Raman spectroscopy using six laser excitation wavelengths located in the electronic absorption band of the S3molecule (406.7–514.5 nm). With excitation wavelengths close to the S3λmax(395 nm) the spectra are mainly resonance enhanced. With the excitation located in the S3electronic absorption band edge the observed resonance Raman spectra are mainly due to the vibrationally excited molecules. Most Raman lines involve transitions between overtone or combination levels of the symmetric stretching (ν1) and symmetric bending (ν2) modes. The comparison of spectra of samples with various34S contents recorded with various excitation wavelengths enable us to determine the ω10and ω20harmonic wavenumbers and the anharmonicity constantsx 011x 022andx 012, for32S3and34S3. New assignments are proposed for all Raman lines observed. A valence force field treatment with the calculated geometryrss= 1.988 Å and α = 117° yields force constants ƒr= 3.91 mdyn Å−1and ƒrr= 0.36 mdyn Å−1. These force constants are compared with those of the parent X2or X3molecul

ISSN:0377-0486    

DOI:10.1002/jrs.1250240103

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractVibrational studies on the neuropentapeptide Leu5‐enkephalin were performed for the crystal state where different specific conformations can arise. In the present case, the peptide adopts a double fused folded conformation (β‐turn), the presence of which in the crystal state is directly related to the nature of the solvent used for its crystallization. This study completes other work relating to similar conformations of isolated molecules. It can be seen that specific interactions in the crystal state perturb to a large extent the vibrational relationships between the amide frequencies and the specific sets of dihedral angles characteristic of the particular type of turn. The tyrosyl moiety and its frequency dependence on its hydrogen bond state was especially investigated both for the Fermi resonance and the hydroxyl bending m

ISSN:0377-0486    

DOI:10.1002/jrs.1250240104

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe Raman spectra (3400–10 cm−1) of liquid and solid 3‐methyl‐3‐vinylcyclopropene, C3H2(CH3)CHCH2, and its isotopomer C3D2(CH3)CHCH2were recorded. The temperature dependence of some band intensities and qualitiative depolarization ratios show that the thermodynamically preferred conformation iss‐trans. The structural parameters and conformational stability ofs‐transandgaucherotamers were obtained fromab initiocalculations by employing both 3–21G and 6–31G* basis sets. Barriers to internal rotation and fundamental vibrational frequencies were calculated utilizing the 3–21G basis set. Theab initioresults are consistent with the experimentally indicated greater stability of thes‐transrelative

ISSN:0377-0486    

DOI:10.1002/jrs.1250240105

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe excitation profiles of several Raman bands oftrans‐azobenzene solution in carbon tetrachloride were measured in resonance with the first allowed electronic transition peaked around 320 nm. The experimental results were analysed by means of a multi‐mode Franck–Condon model to obtain some excited state molecular parameters; such parameters were found to reproduce well the red side of the absorption band whereas some inconsistencies between experiment and calculation persist on the UV side. This has been tentatively explained as due to the contribution of a higher energy electronic state whose absorption band is peaked around 287 nm and which may slightly affect the parameters obt

ISSN:0377-0486    

DOI:10.1002/jrs.1250240106

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe performances of a multiplexed near‐infrared (NIR) germanium detector and of a InGaAs photodiode‐array detector are reported. Their use with an Nd: YAG laser at 1.064 μm to obtain high‐quality fluorescence‐free Raman spectra of micro‐samples is illustrated. A comparison with Fourier transform Raman spectra of much larger samples demonstrates that NIR multi‐channel Raman spectroscopy is competitive for fluorescence‐free measurement of

ISSN:0377-0486    

DOI:10.1002/jrs.1250240107

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

ISSN:0377-0486    

DOI:10.1002/jrs.1250240101

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY