A. Nino et al., A STUDY OF QUADRATIC PLUS GAUSSIAN PLUS COSINE FUNCTIONS FOR THE SIMULTANEOUS DESCRIPTION OF INTRAMOLECULAR TORSION AND INVERSION, Journal of molecular structure, 318, 1994, pp. 237-242
The use of more realistic potential energy functions than the usual do
uble Fourier series expansion is investigated for the description of c
oupled inversion and torsional motion. A quadratic-gaussian expression
is used for the description of the inversion motion whereas a trigono
metric expansion is used for the torsion. The coupling between the two
motions is introduced into the trigonometric function as a phase fact
or that depends on the inversion angle. The treatment is applied to th
e carbonyl hydrogen wagging and methyl torsion in the first excited el
ectronic state of acetaldehyde. The use of experimental results in con
junction with ab initio data for the determination of the potential fu
nction is also tested.