The calculation of force constants and normal coordinates—VI. Force constants of the silyl group

Abstract

Normal coordinate calculations have been carried out for a number of molecules of three-fold symmetry containing the silyl group. All available data on frequencies and Coriolis interaction constants for all isotopic species (where possible) were used in force constant refinement calculations. Since these data were not sufficient to fix the general harmonic force field (GFF), the silyl group force field was constrained according to the model which has been successfully applied to the methyl group in previous papers in this series. In general, the refinements were made independently for each molecule, and the results show a pleasing degree of uniformity for the silyl group when the nature of the fourth atom attached to the Si atom is taken into account. On the basis of the transferability of force constants in almost identical molecules, some assignments for silyl acetylene and methyl silyl acetylene are questioned, and alternative assignments proposed.