Methanol and deuterated species: Infrared data,valence force field,rotamers, and conformation

New infrared measurements of gaseous and matrix-isolated methanol and 7 deuterated species are presented and analyzed. A revised assignment for the species CH₃OH(D) and CD₃OH(D) is used to determine 15 significant parameters of a valence force field by a converged simultaneous least-squares adjustment to 44 observed fundamentals. The respective frequencies calculated for the rotamers of CH₂DOH(D) and CHD₂OH(D) turn out to be a valid prediction as they are used to assign 78 observed fundamentals of the species with partially deuterated methyl groups. The values of the 15 force constant parameters are refined by including all 122 observed fundamentals. The force field contains significant deviations from local C_3v symmetry of the methyl group. Such an asymmetry, in the CH-stretching diagonal part, produces a difference of about 10 cm^?1 in the zero point energy of symmetric and asymmetric rotamers of the species with partially deuterated methyl groups. Calculations based on equilibrium structures with and without methyl tilt yield better agreement with observed data in the nontilted case. A preliminary calculation of relative intensities reproduces the major effects of isotopic substitution and rotational isomerism. Experimental evidence for the staggered conformation is obtained from a comparison of observed data with calculated results based on staggered and eclipsed models.