The vibrational overtones of SiH₄ isotopomers: experimental wavenumbers, assignment, ab initio dipole moment surfaces and intensities

The overtone spectra of SiHD3, SiH2D2 and SiH3D in the range 2000–9000 cm−1 have been measured up to 720000 Pa m using a Bruker 120HR interferometer. The transition frequencies and intensities are reported. The observed band centers are found to be in good agreement with the predictions from high order canonical Van Vleck perturbation theory (CVPT) calculations. A four-dimensional Si–H stretching dipole moment surface (DMS) has been determined from coupled cluster [CCSD(T)] methods and expanded using a bond dipole model and a Cartesian model. The band intensities of the Si–H and Si–D stretching transitions have been computed employing these expansions and a local mode force field optimized to the observed band centers. The calculations agree reasonably well with observations for most bands. The vibrational intensity anomaly in the third local mode manifolds is partly reproduced and is attributed to the cancellation of linear and quadratic terms in the DMS