Item

Abstract

The SiH₂D₂ asymmetric top has nine vibrational modes, five of them forming a pentad strongly perturbed by Coriolis interactions. High-level ab initio calculations of SiH₂D₂ have been performed which yield numerous spectroscopic parameters related to the harmonic and anharmonic force fields. The bending pentad comprising ν₄(A₁), ν₇(B₁), ν₅(A₂), ν₉(B₂), and ν₃(A₁) has been studied by high-resolution Fourier transform spectroscopy; the region 600–1050 cm⁻¹ has been investigated with a resolution of ca. 4 × 10⁻³cm⁻¹. Raman BOXCARS spectroscopy has been used for the infrared inactive ν₅ band. The Raman apparatus function was 0.0054 cm⁻¹. Assignments of about 4000 transitions including all bands have been made, mostly employing ground state combination differences techniques, and a global fit has been performed. The fundamentals ν₄ (681.624 cm⁻¹), ν₇ (742.640 cm⁻¹), ν₅ (842.381 cm⁻¹), ν₉ (859.750 cm⁻¹), and ν₃ (942.741 cm⁻¹) are strongly coupled by A-, B-, and C-type Coriolis interactions, and ab initio predictions of these interaction parameters were used to set up a network of interactions that was refined by the experimental data. The global standard deviation for the entire body of data is 7.1 × 10⁻⁴cm⁻¹. Satisfactory synthetic spectra which are very sensitive to relative signs of dipole moment derivatives and Coriolis interaction constants were obtained with the guidance ofab initiocalculations. Finally, fair to good agreement of experimental and ab initio calculated molecular parameters was obtained. For the first time, a complete analysis of the pentad of SiH₂D₂ in the 10–16 μm region has been carried out. A full set of rovibrational parameters is given for these five interacting levels, including first and second order Coriolis interaction constants.