VIBRATIONAL-SPECTRA OF ZINC, CADMIUM AND MERCURY DIMETHYL SPECIES

Infrared and Raman spectra have been obtained in the gas phase for the species (M(CH3)2)-C-12, (MCH3)2)-C-13, M(C-12D3)2 and M(C-13D3)2, where M = Zn, Cd and Hg. All but one of the skeletal bending modes are observed directly in the infrared. C-13 frequency shifts confirm the assignment of a number of combination and overtone bands, including the 1300 cm-1 bands of Zn(CH3)2 and Cd(CH3)2 which arise from nu10 + nu14. Infrared spectra in the 1400-1500 cm-1 region are difficult to interpret but the evidence points to both the delta(as)CH3 modes lying near 1445 cm-1. A number of Fermi resonances affecting delta(s)CD3 levels are identified in the d6 species. Some features of the nu(as)CH3 bands can be explained in terms of existing free internal rotor theory. Observed values of C-13 frequency shifts are generally in good agreement with those from previous scaled ab initio calculations. There is an urgent need for high resolution studies of jet-cooled samples.