FOURIER TRANSFORM SPECTRA AND INVERTED TORSIONAL STRUCTURE FOR A $CH_{3}$-BENDING FUNDAMENTAL OF $CH_{3}OH$
Loading...
Date
2000
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
The high-resolution Fourier transform spectrum of $CH_{3}OH$ has been investigated in the $1400-1650 cm^{-1}$ region, containing the $CH_{3}$-bending fundamental bands. Twenty-two perpendicular $\Delta K=+1$ subbands have been identified so far, with origins ranging from 1490 to $1570 cm^{-1}$ for transitions $K=2 \leftarrow 1$ up to $11 \leftarrow 10$ for various torsional symmetries. Assignment of the subbands to the $\nu_{4}$ in-plane ($A^{\prime}$) or $\nu_{10}$ out-of-plane ($A^{\prime\prime}$) asymmetric methyl-bending modes is not yet clear, but the one subband so far observed with resolved K-doublet structure suggests c-type selection rules consistent with a $\nu_{10}$ vibrational assignment. The pattern of the $K$-reduced torsion-vibration energy $\tau$-curves is inverted compared to the normal 1- dimensional picture for $n = 0$ torsional levels, in agreement with prediction based on fitting torsional variation of ab initio $CH_{3}$-bending frequencies to a local mode model. However, the periodicity of the curves is unusual and significantly different from the ground state. The vibrational energy for the bending mode is $1481 cm^{-1}$, and the mean B-value is $0.008 cm^{-1}$ higher than that of the vibrational ground state.
Description
Author Institution: Department of Physical Sciences, University of New Brunswick; Physikalisch-Chemisches lnstitut, Justus Liebig University; Steacie Institute for Molecular Sciences, National Research Council of Canada