Experimental and theoretical investigation of the Raman and hyper-Raman spectra of acetonitrile and its derivatives

Olivier Quinet, Benoît Champagne, Vincent Rodriguez

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Abstract

The Raman and hyper-Raman spectra of acetonitrile and its deuterated analog have been investigated by combining experimental analysis and theoretical interpretation. It has been observed that the Raman spectra can easily be reproduced at both the Hartree-Fock and Møller-Plesser second-order levels of approximation and that for these fundamental transitions, inclusion of anharmonicity effects is not essential. On the other hand, the hyper-Raman spectra are more difficult to simulate and interpret. In particular, electron correlation has to be included in order to describe properly the intensity of the CN stretching mode. Then, a pseudo-C∞ν symmetry was assumed to better fit the experimental observations. This accounts for the fact that the a1- and e-symmetry modes correspond to time-decoupled vibrations. The e-symmetry modes, associated with nuclear motions perpendicular to the molecular axis are indeed subject to relaxation processes and, except the CCN bending mode, not visible in the hyper-Raman spectra of acetonitrile or of its deuterated analog. This assumption is supported by the gradual decrease of the phenomenon when going from acetonitrile to trichloroacetonitrile, where the presence of the heavier chlorine atoms in the latter reduces the relaxation processes.

Original languageEnglish
Article number244312
JournalThe journal of chemical physics
Volume124
Issue number24
DOIs
Publication statusPublished - 10 Jul 2006

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acetonitrile
Raman scattering
Raman spectra
Derivatives
Relaxation processes
symmetry
analogs
Electron correlations
Chlorine
Stretching
chlorine
inclusions
Atoms
vibration
approximation
atoms
electrons

Cite this

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