Line Strengths of Torsion-Rotation Transitions of Methanol for J less than or equal} 14 and vt less than or equal} 2 From Hamiltonian Based Calculations

Published

November 9, 1998

Author(s)

M A. Mekhtiev, P D. Godfrey, Jon T. Hougen

Abstract

Line strengths have been obtained for methanol, based on matrix elements of the dipole moment operator evaluated in a set of torsion-rotation eigenfunctions. The latter were obtained from the parameters and effective Hamiltonian giving the best spectral fit available for a data set containing J less than or equal} 20, K less than or equal} 14 and v_t less than or equal} 1 microwave and far infrared transitions. The dipole moment function was represented as a Fourier expansion in the torsional angle γ. Values for the permanent components υ_a and υ_b were obtained from experiment; values for their cos3γ variation and for the sin3γ variation of υ_c were obtained from quantum chemistry molecular orbital calculations. The approach described allows calculation of the line strength for any transition which satisfies the general selection rule A₁ <-> A₂, or E <->E. A complete set of such line strengths for all methanol torsion-rotation transitions involving levels with J less than or equal} 22, K less than or equal} 14 and v_t less than or equal} 2, and with intensities and frequencies above the rather small cutoff limits of 10^-6u2 and 1 kHz, respectively, together with individual contributions from the permanent and γ-varying dipole moment components, have been tabulated and are available from the anonymous ftp.monash.edu.au/pub/chem/1998a site.

Citation

Journal of Molecular Spectroscopy

Pub Type

Journals

Keywords

infrared spectroscopy, intensity calculations, methanol, microwave spectroscopy, rotational lines, theory

Citation

Mekhtiev, M. , Godfrey, P. and Hougen, J. (1998), Line Strengths of Torsion-Rotation Transitions of Methanol for J {less than or equal} 14 and v_t {less than or equal} 2 From Hamiltonian Based Calculations, Journal of Molecular Spectroscopy (Accessed July 27, 2024)