THEORETICAL ROTATIONAL VIBRATIONAL-SPECTRUM OF SIH2 (X1A1 AND A 3B1)

The three-dimensional potential energy and electric dipole moment functions of the X1A1 and a B-3(1) states of SiH2 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 X1A1 SiH2. In the variational calculations all anharmonicity effects and vibration-rotation couplings have been considered. The equilibrium spectroscopic constants for SiH2, SiD2, and SiHD (X1A1 and a B-3(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 1nu1 and 2nu2 bands have almost equal integrated band intensities in the absorption spectrum and overlap with the 1nu3 band between 1800 and 2300 cm-1. For the most intense transitions absolute line intensities are given. In the electronic ground state of SiH2 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.