Normal coordinate analyses for trimethylantimony(V) dihalides: A comparison of three force fields

Approximate normal coordinate analyses have been carried out for the series (CH₃)₃SbX₂ (X = F, Cl, Br, and I) assuming a molecular symmetry of D_3h and that the methyl groups behave as single atoms. Sets of seven force constants have been evaluated for each molecule using each of the following force fields: general valence, modified Urey-Bradley, and orbital valence. The fundamental vibrational frequencies have been evaluated using these force constants and have been compared with the experimentally observed values published previously. The orbital valence force constants generally led to better agreement between calculated and observed frequencies. Trends in the force constant values are discussed briefly.