Ab initio study of torsional vibrations of the fluoral molecule in the ground state

A comparative analysis of various approximations used to solve the problem on the torsional motion of the CF3 group in the trifluoroacetaldehyde molec ule is presented. It is considered how the estimates of torsional transitio n frequencies are affected by the choice of a basis set for an ab initio ca lculation, by the method of inclusion of electron correlation, by the geome trical model of the molecule, and by the method of determination of nuclear energy levels. The results are also considered for the related acetaldehyd e molecule. The Appendix briefly defines the structure of the energy levels of torsional symmetric top vibrations.