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.