A STUDY OF QUADRATIC PLUS GAUSSIAN PLUS COSINE FUNCTIONS FOR THE SIMULTANEOUS DESCRIPTION OF INTRAMOLECULAR TORSION AND INVERSION

The use of more realistic potential energy functions than the usual double Fourier series expansion is investigated for the description of coupled inversion and torsional motion. A quadratic-gaussian expression is used for the description of the inversion motion whereas a trigonometric expansion is used for the torsion. The coupling between the two motions is introduced into the trigonometric function as a phase factor that depends on the inversion angle. The treatment is applied to the carbonyl hydrogen wagging and methyl torsion in the first excited electronic state of acetaldehyde. The use of experimental results in conjunction with ab initio data for the determination of the potential function is also tested.