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A New Torsion-Rotation Fitting Program for Molecules with a Six-Fold Barrier: Application to the Toluene Microwave Spectrum

Published

Author(s)

Vadim V. Ilyushin, Zbigniew Kisiel, Lech Pszczolkowski, Heinrich Maeder, Jon T. Hougen

Abstract

A new program is described for fitting rotation-torsion energy levels in the molecules like toluene, in which the frame (C6H5) has C2v symmetry and the methyl top has C3v symmetry, i.e., for molecules where the internal rotation barrier is expanded in cos6n, where  is the internal rotation angle and n = 1, 2, . The program is based on the theoretical framework developed by S rensen and Pedersen in their application of the Longuet-Higgins permutation-inversion group G12 to the microwave spectrum of CH3NO2. It is specifically designed for six-fold barrier molecules, and allows the user to select almost any symmetry-allowed torsion-rotation term for inclusion in the fitting Hamiltonian. This program leads to a very successful fit of transitions in the toluene microwave spectrum characterized by J  30, Ka  12, and the free rotor quantum number |m|  3. In these fits we included both published and rather extensive unpublished new measurements, for which fits using other torsion-rotation programs have not been very successful. The fit presented here used 23 parameters to give an overall standard deviation of 7.6 kHz for the 362 transitions.
Citation
Journal of Molecular Spectroscopy
Volume
259

Keywords

G12 Permutation-Inversion Group, Internal Rotation, Least-Squares Fit, Microwave Spectrum, Six-Fold Barrier, Toluene

Citation

Ilyushin, V. , Kisiel, Z. , Pszczolkowski, L. , Maeder, H. and Hougen, J. (2009), A New Torsion-Rotation Fitting Program for Molecules with a Six-Fold Barrier: Application to the Toluene Microwave Spectrum, Journal of Molecular Spectroscopy, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=903188 (Accessed April 16, 2024)
Created October 28, 2009, Updated October 12, 2021