SIMULATION OF VIBRATIONAL-SPECTRA OF ISOTOPIC BENZENES BY AN EXTENDEDMOLECULAR MECHANICS METHOD

Vibrational spectra of benzene and benzene-d6 in the gas and liquid ph ase have been simulated by a molecular mechanics method including the calculation of equilibrium structures, thermodynamic quantities, norma l frequencies and vibrational transition probabilities. The potential parameters have been estimated by referring to the observed frequencie s of benzene, benzene-d6 and 1,3,5-benzene-d3 and also to results of a b initio calculations. Four and ten independent parameters are require d, respectively, for elucidating the infrared absorption and Raman int ensities of these compounds in the gas and liquid phase. The infrared absorption spectrum of benzene-d1 is reproduced well by using the pote ntial and the intensity parameters estimated for benzene and benzene-d 6. The change of relative band intensities on the phase change has bee n elucidated in terms of the change of various intensity parameters.