Ab initio calculations and high-resolution spectroscopy of the bending pentad of SiH2D2 in the 10-16 mu m region

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 spectroscop ic parameters related to the harmonic and anharmonic force fields. The bend ing pentad comprising nu(4)(A(1)), nu(7)( B-1), nu(5)(A(2)), nu(9)(B-2), an d nu(3)(A(1)) has been studied by high-resolution Fourier transform spectro scopy; the region 600-1050 cm has been investigated with a resolution of ca . 4 x 10(-3) cm(-1). Raman BOXCARS spectroscopy has been used for the infra red inactive nu(5) band. The Raman apparatus function was 0.0054 cm-l. Assi gnments of about 4000 transitions including all bands have been made, mostl y employing ground state combination differences techniques, and a global f it has been performed. The fundamentals nu(4)(681.624 cm(-1)), nu(7)(742.64 0 cm(-1)), nu(5)(842.381 cm(-1)), nu(9)(859.750 cm(-1)), and v, (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 gl obal standard deviation for the entire body of data is 7.1 x 10(-4) cm(-1). Satisfactory synthetic spectra which are very sensitive to relative signs of dipole moment derivatives and Coriolis interaction constants were obtain ed with the guidance of ab initio calculations. Finally, fair to good agree ment of experimental and ab initio calculated molecular parameters was obta ined. For the first time, a complete analysis of the pentad of SiH2D2 in th e 10-16 mu m region has been carried out. A full set of rovibrational param eters is given for these five interacting levels, including first and secon d order Coriolis interaction constants. (C) 1998 Academic Press.