Vibrational Spectra of Triiodomesitylen: Combination of DFT Calculations and Experimental Studies. Effects of the Environment - Université de Rennes Accéder directement au contenu
Article Dans Une Revue Journal of Physical Chemistry A Année : 2008

Vibrational Spectra of Triiodomesitylen: Combination of DFT Calculations and Experimental Studies. Effects of the Environment

Ali Boudjada
  • Fonction : Auteur
Fahima Boudjada
  • Fonction : Auteur
Alain Moréac
Stewart F. Parker
  • Fonction : Auteur

Résumé

A study of the internal vibrations of triiodomesitylene (TIM) is presented. It is known from X-rays diffraction at 293 K that the molecule has nearly D3h symmetry because of the large delocalization of the methyl protons. By using Raman and infrared spectra recorded at room temperature, a first assignment is done by comparing TIM vibrations with those of 1,3,5-triiodo- and 1,3,5-trimethyl-benzene. This assignment is supported by DFT calculations by using the MPW1PW91 functional with the LanL2DZ(d,p) basis set and assuming C3h symmetry. The agreement between the calculated and experimental frequencies is very good: always better than 97% for the observed skeletal vibrations. The calculations overestimate the methyl frequencies by 7%, and experiment shows only broad features for these excitations. Because a neutron diffraction study had established that the TIM conformation at 14 K is not exactly trigonal, new theoretical calculations were done with Cs symmetry. This shows that all previous E′ and E″ modes of vibration are split by 2−12 cm−1. This is confirmed by infrared, Raman, and inelastic neutron scattering spectra recorded below 10 K. Apart from two frequencies, all the TIM skeleton vibrations have been detected and assigned by using Cs symmetry. For the methyl vibrations, experiment has confirmed the splitting of the previously degenerate modes; only some small discrepancies remain in the assignment. This is partly due to the difference of the model conformation used in the calculations and the crystallographic one. All these results confirm that each of the three methyl groups has not only its own tunnel splitting but also a different specific spectroscopic behavior for all the molecular modes.

Domaines

Chimie

Dates et versions

hal-00344708 , version 1 (05-12-2008)

Identifiants

Citer

Jean J. Meinnel, Ali Boudjada, Abdou Boucekkine, Fahima Boudjada, Alain Moréac, et al.. Vibrational Spectra of Triiodomesitylen: Combination of DFT Calculations and Experimental Studies. Effects of the Environment. Journal of Physical Chemistry A, 2008, 112 (44), pp.11124-11141. ⟨10.1021/jp802621w⟩. ⟨hal-00344708⟩
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