INFRARED INDUCED ISOMERIZATION EFFICIENCY FOR CH2D-CH2D ISOLATED IN RARE-GAS MATRICES - INFLUENCE OF THE VIBRATIONAL-EXCITATION AND OF THE MEDIUM

The resonant excitation of 13 vibrational states of the gauche and the trans forms of CH2D-CH2D isolated in a xenon matrix has been performe d with the laser radiation provided by the free electron laser CLIO an d by an optical parametric oscillates configuration. The determination of the sample composition by infrared spectroscopy gives the energy d ependence of the conformational inversion quantum yield in the 1000-30 00 cm(-1) domain. This reaction proves the coupling of the molecular i nternal rotation with the laser excited vibrational mode. We observe a global increase of the isomerization efficiency with the excitation e nergy, but with large fluctuations in the energy dependence. The incre ase is interpreted as due to the addition of new coupling channels whe n higher states of the vibrational ladder are excited, whereas the flu ctuations are a signature of specific molecular couplings. The influen ce of the temperature and of the nature of the rare gas matrix on the isomerization rate emphasizes the key role of the intermolecular inter actions along the reaction path. (C) 1997 American Institute of Physic s.