Torsion and CO-stretching vibration interactions in methanol

Abstract

A model Hamiltonian is constructed to investigate the vibration–torsion–rotational interaction in methanol. The model Hamiltonian is based on the formulation of reduction of Hamiltonian, in which the CO-stretching mode ν 8, the large-amplitude torsion mode ν 12 and the three degrees of freedom that correspond to the overall rotation of the molecule, are considered simultaneously. This Hamiltonian is used to carry out an analysis of already published data for CH 3OH with v co ⩽ 1 (the CO-stretching vibrational quantum number), v t ⩽ 4 (the torsional quantum number), and J ⩽ 5 (the overall rotational quantum number). The relative locations of the CO-stretch vibrational ground state and the fundamental state are well reproduced for torsional states with v t ⩽ 4 and J ⩽ 5. An effective potential energy surface that describes ν 8 and ν 12 modes is obtained from this analysis. The present analyses show that a variety of resonance interactions can affect states for energies larger than 1100 cm −1.