Theoretical rotational—vibrational spectrum of SiH 2 (X 1A 1 and a 3B 1)

Abstract

The three-dimensional potential energy and electric dipole moment functions of the X 1A 1 and a 3B 1 states of SiH 2 have been calculated from highly correlated CEPA electronic wavefunctions. The analytic representations of these functions have been used in perturbational and variational calculations of the rotationally resolved absorption spectrum of X 1A 1 SiH 2. In the variational calculations all anharmonicity effects and vibration—rotation couplings have been considered. The equilibrium spectroscopic constants for SiH 2, SiD 2, and SiHD (X 1A 1 and a 3B 1) isotopomers and absolute integrated band intensities are given. The calculated vibrational band origins agree to within 10–40 cm −1 with available gas phase experimental values. It has been shown that due to strong Fermi resonances the 1ν 1 and 2ν 2 bands have almost equal integrated band intensities in the absorption spectrum and overlap with the 1ν 3 band between 1800 and 2300 cm −1. For the most intense transitions absolute line intensities are given. In the electronic ground state of SiH 2 the vibrational band intensities of the fundamental absorption transitions are found to be more intense than the pure rotational transition in the vibrational ground state.