Theoretical and computational study of internal motions in some smallmolecules

This work contains studies in theoretical and computational spectroscopy of methanol, partially deuterated silane, and bismutine. Vibrational spectra of methanol have been simulated in the fundamental, first C-H stretching overtone, and O-H stretching overtone regions using both normal and local mode models. A vibration-torsion local mode model based on curvilinear internal coordinates has been employed to find a physical interpretation for torsionally splitted vibrational energy levels of methanol. A high-level ab initio quartic anharmonic force field for methanol has been computed and used in the calculation of normal mode spectroscopic parameters with perturbation theory. Ro-vibrational spectroscopic parameters for the near local mode stretching states of H3SiD have been calculated from an ab initio force field and applied to the analysis of high-resolution Fourier transform infrared and laser-photoacoustic spectra. Corrections to the bond stretching kinetic energy coefficients have been calculated due to the presence of rigid constraints in the bending degrees of freedom for C3v pyramidal molecules stibine, ammonia, bismutine, and arsine. Stretching vibrational overtone spectra of bismutine have been analyzed with a simple stretching vibrational local mode model.