THE CONFORMATIONAL PROBLEM STUDIED THROUGH THE TORSIONAL RAMAN-SPECTRA OF CH2DCH2D, CHD(2)CHD(2), AND CH2DCHD(2)

The torsional Raman spectra of CH2DCH2D, CHD2CHD2, and CH2DCHD2, recor ded with an improved conventional Raman spectrometer, are interpreted here in the frame of an exact rotational-torsional Hamiltonian. The ki netic and potential operators of this Hamiltonian are discussed in det ail, showing that the term responsible for the existence of two distin guishable conformers is of kinetic nature. For CH2DCH2D and CHD2CHD2 i t is shown how to separate the rotational and the torsional motions by means of an appropriate choice of the molecular axis system. The wave numbers and intensities of both torsional Raman spectra are satisfact orily reproduced within the limits of the experiment with the followin g effective potential parameters: CH2DCH2D, V3 = 1002 cm-1, V6 = 6.0 c m-1; CHD2CHD2, V3 = 995 cm-1, V6 = 7.3 cm-1. For CH2DCHD2, only partia lly tractable in the present approach, an approximate estimate of V3 = 995 cm-1 has been obtained. Besides the quantitative interpretation o f the torsional spectra, a discussion of the main facts of the conform ational problem in connection to the spectroscopic observation is pres ented. In particular, the induced conformational transitions described here may contribute to the understanding of the elementary photoisome rization processes in molecules of the type AX2Y-AX2Y.