post-Hartree Fock Methods Research Articles

AB initio investigations of symmetric rotor models for small trifluoromethyl substituted molecules

Gas phase structural information is available for many trifluoromethyl substituted molecules. For practical reasons, this has been interpreted using symmetric rotor models for the trifluoromethyl top, although there is evidence that this approximation is not a complete model for the equilibrium structure of the molecules. Fluorine is also known to be a difficult substituent to represent with conventional SCF techniques; accuracy often depends on elaborate basis sets and post Hartree-Fock methods. However, for the purpose of this study, ab initio investigations have been made of trifluoroacetylfluoride, trifluoroacetic acid, and perfluoroacetic acid to determine the extent to which the conventional single determinant calculations based on the symmetric rotor model are in agreement with the experimental interpretations of the molecular structure. In particular, optimized geometries, vibrational analyses, conformational structures and barriers to rotation are presented.