Vibrational assignments and force field calculations for trimethylarsenic dichloride,dibromide and their deuterated analogs

Raman and infrared spectra have been recorded for trimethylarsenic dichloride, dibromide and their deuterated analogs and vibrational assignments were made for the skeletal modes of these compounds. The spectra of the dichloride and its deuterated analog were interpreted in terms of a trigonal bipyramidal structure, D_3h symmetry, whereas the spectra of the dibromides were interpreted using the ionic model, [(CH₃)₃AsBr]⁺Br⁻, having C_3v symmetry. Using a generalized valence force potential field, normal coordinate analyses data were obtained for the dichloride and the dibromide. Included in this data are potential energy distributions for a set of symmetry coordinates. The force fields obtained for the dichloride and dibromide were used to calculate frequencies for the corresponding deuterated compounds. The discrepancies between the observed and calculated frequencies for the deuterated compounds are discussed in terms of the assumptions made.