TWO-TOP TORSIONAL ASSIGNMENTS IN THE $A^{1}A_{u}(S_{1}) - X^{1}A_{g}(S_{0})$ TRANSITION OF BIACETYL $CH_{3}C(=O)C(=O)CH_{3}$
Loading...
Date
2004
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
The laser-induced fluorescence excitation spectrum of the biacetyl $A^{1}A_{u}(S_{1}) - X^{1}A_{g}(S_{0})$ transition in the region from 22 182 to $28 000 cm^{-1}$ shows a complicated absorption line spectrum, which is believed to arise from a long progression in the torsional vibrations of the two equivalent methyl tops in this molecule. In this talk we discuss three topics: (i) a numerical calculation of these energy levels using a kinetic and potential energy formalism and preliminary constants from the $literature,^{a}$ (ii) a qualitative description of the calculated energy level pattern using local mode ideas applied to the two equivalent methyl rotors as well as $G_{36}$ permutation-inversion group symmetry species, and (iii) a comparison of the calculated energy levels with the low-resolution spectrum taken in the region from 0 to $500 cm^{-1}$above the A-X band origin at IAMS in Taipei. The levels with one quantum of torsional excitation are best described by a normal mode formulation, but levels with more than one quantum of torsional excitation are better described by a local mode formulation. Good agreement with the low resolution spectrum is obtained, but full confirmation of the interpretation will require high resolution studies of some additional bands.
Description
$^{a}$M. L. Senent, D. C. Moule, Y. G. Smeyers, A. Toro-Labb\'{e}, and F. J. Peqalver, J. Mol. Spectrosc. 164, 66-78 (1994).
Author Institution: Department of Applied Chemistry, National Chiayi University; Department of Applied Chemistry, Institute of Atomic and Molecular Sciences, Academia Sinica; Optical Technology Division, National Institute of Standards and Technology
Author Institution: Department of Applied Chemistry, National Chiayi University; Department of Applied Chemistry, Institute of Atomic and Molecular Sciences, Academia Sinica; Optical Technology Division, National Institute of Standards and Technology