Xg. Wang et El. Sibert, A nine-dimensional high order perturbative study of the vibration of silane and its isotopomers, J CHEM PHYS, 113(13), 2000, pp. 5384-5400
The vibrations of silane isotopomers with T-d, C-3v, and C-2v symmetry are
studied by means of high order canonical Van Vleck perturbation theory (CVP
T). Transforming the quartic ab initio force field of Martin, Baldridge, an
d Lee [Mol. Phys. 95, 254 (1999)] into curvilinear normal coordinates, CVPT
is used to calculate energies that agree well with experimental data. Both
low energy stretch-bend combination bands and high energy stretch local mo
de bands of silane up to 12 000 cm(-1) are well reproduced. The choice of p
olyad quantum number is discussed with respect to different molecules. Comp
aring sixth- to eighth-order level of theory, most of the levels agree to w
ithin 0.1 cm(-1). Spectroscopic constants are given for all the major isoto
pomers. The construction of the full cubic and quartic resonance operators
for symmetric top species are summarized. The Si-H and Si-D stretch modes o
f T-d and C-3v symmetry species are studied with a 4D stretch variational m
odel using both the fitted three-parameter potential and the quartic ab ini
tio stretch potential. Large energy level differences between these two cal
culations indicate that the fitted potential constants of the stretch varia
tional model are different from those derived directly from the ab initio s
urface. By comparing with the nine-dimensional CVPT calculation, it is show
n that the direct and indirect Fermi resonances are responsible for the ina
bility of the four-dimensional model to fit some stretch levels. (C) 2000 A
merican Institute of Physics. [S0021- 9606(00)01237-X].