THE SPECTROSCOPY OF 9,10-CYANOMETHYLANTHRACENE IN A SUPERSONIC FREE JET: METHYL GROUP ROTATION
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Date
1997
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Publisher
Ohio State University
Abstract
The molecule 9, 10-cyanomethylanthracene has been studied by means of laser spectroscopy and {ab-initio} calculations. The fluorescence excitation spectrum of cyanomethylanthracene in a supersonic free jet shows a prominent torsional progression due to the hindered internal rotation of the methyl group. A $2-5 cm^{-1}$ splitting of many vibrational bands has been observed. The potential energy curves for methyl group rotation have been obtained with the use of RHF/6-31$G^{*}$* for the ground $(S_{a})$ and CIS/3-21G for the excited state $(S_{1})$. The calculated energy barrier for the methyl rotation in the $S_{0}$ state is $72 cm^{-1}$ and is considerably higher than the $22 cm^{-1}$ barrier calculated for the $S_{1}$ state. The symmetry of the barriers are 6-hold in the $S_{a}$ and 4-hold in the $S_{1}$ states. The methyl torsion is a sensitive probe of the structural changes following $S_{1} \leftarrow S_{0}$ excitation. The possibility of photochemical isomerisation of cyanomethylanthracene to yield Dewar anthracene will be discussed.
Description
Author Institution: Institute of Physical Chemistry, Polish Academy of Sciences; The James Franck Institute and the Department of Chemistry, The University of Chicago; Department of Chemistry, Warsaw University; Department of Chemistry, University of Arizona