Study of the stretching vibrational band intensities of XH_4 molecules employing four-dimensional ab initio (X=C and Sn) and effective (X=C and Si) dipole moment surfaces

摘要

Stretching vibrational band intensities of XH_4 molecules were investigated employing four-dimensional ab initio (X=C and Sn) and effective (X=C and Si) dipole moment surfaces (DMS) in combination with the local mode potential energy surfaces. The ab initio DMS of CH_4 and SnH_4 calculated at the coupled cluster CCSD(T) level of theory reproduced most of the observed intensities within a factor of 1.5. The effective DMS of CH_4 and SiH_4 were obtained by adjusting some selected high-order terms in the ab initio DMS to fit the observed intensities. They were applied to the corresponding deuterated isotopomers yielding better results than the ab initio DMS. The intensities of the combination bands are mainly due to he interbond cross terms in the DMS for SiH_4, GeH_4, and SnH_4, while for CH_4, both diagonal and cross terms are important. The relatively strong combination band that has comparable intensity with the pure overtone was predicted at the fourth local mode manifold for SnH_4.