Vibrational potential function of 1,1,1-trihalide dimethyl sulfides, CH3SCX3, X = F,Cl

A new investigation is presented on the vibrational potential function of t he 1,1,1-trifluoro- and 1,1,1-trichlorodimethyl sulfide molecules. Based up on the recently developed common force field method, we have estimated the 'group force constants' of the SCH3 group of atoms, common to these two mol ecules. Ab initio calculations have been performed on these molecules in th e HF approximation, using a triple Zeta plus polarization (cc-pVTZ) basis s et. The force constants are refined in internal and symmetry coordinate rep resentations, concluding that the internal coordinates provide a better rep resentation for the refinements. The observed frequencies are reproduced wi thin a 1% relative deviation. Small elements in ab initio calculated force fields are proved to be irrelevant. (C) 2000 Elsevier Science B.V. All righ ts reserved.