Torsional Splittings in Small-Amplitude Vibrational Fundamental States of Methanol-Type Molecules

Published

May 1, 2001

Author(s)

Jon T. Hougen

Abstract

Group-theoretical methods are used to show that inverted torsional splittings in fundamental levels of small-amplitude vibrations of methanol-like molecules can be understood (and parameterized) in terms of the splittings induced when a high-barrier torsional ground state pair of states of ^tA + ^tE symmetry in the molecular symmetry group G₆ (isomorphic with C_3v) is allowed to interact with small-amplitude vibrational modes of symmetry ^vE in G₆. Such doubly degenerate ^vE vibrational modes arise rather naturally in G₆ for those vibrations of the methyl top in methanol or acetaldehyde (point group C₈) that are analogs of the degenerate stretch, bend, and rocking motions of the methyl group in CH₃-C=C-H (point group C_3v). The present treatment is somewhat different, but still fundamentally similar (as a comparison of model parameters shows), to the recent local mode explanation of inverted torsional splittings in the ^vE + ^vA₁ set of three C-H stretching vibrations in methanol.

Citation

Journal of Molecular Spectroscopy

Volume

207

Issue

No. 1

Pub Type

Journals

Keywords

degenerate vibration, group theory, internal rotation, inverted torsional splitting, vibration-torsion interaction

Citation

Hougen, J. (2001), Torsional Splittings in Small-Amplitude Vibrational Fundamental States of Methanol-Type Molecules, Journal of Molecular Spectroscopy (Accessed April 26, 2024)