tau-Clustering for molecules with large torsional splittings: the nu(7)+nu(8) and 2 nu(8) combination and overtone bands of CH3OH

Line clustering into two groups of differing tau torsional symmetries is co nsidered for parallel infrared vibrational bands of 3-fold internal rotor m olecules with large torsional splittings, such as methanol. In bands involv ing large changes in torsional parameters, the tau -clustering produces a d istinctive pair of Q-branch peaks in the low-resolution spectrum. The origi n of the tau -clustering and the formation of the twin Q-branch peaks are d iscussed together with new subband assignments in Fourier transform spectra of the nu (7) + nu (8) CH3-rock/CO-stretch combination and 2 nu (8) CO-str etching overtone bands of CH3OH, which are good representatives of large an d small changes in torsional parameters, respectively. (C) 2001 Elsevier Sc ience B.V. All rights reserved.