Table of Contents
Laser Chemistry
Volume 1 (1983), Issue 5, Pages 177-183

Observation of Intermode Coupling in the 3μm IR Multiple Photon Excitation of Propylene

Exxon Research and Engineering Co., P. O. Box 45, Linden 07036, New Jersey, USA

Received 14 March 1983

Copyright © 1983 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The mechanism of IR multiple photon excitation through the dense manifold of vibrational states, usually called the quasicontinuum, of a vibrationally excited molecule is one of the unresolved issues in the field of laser chemistry. The effects of deuterium substitution on propylene IR multiple photon excitation are used to identify the vibrational modes leading to efficient excitation. Optoacoustic energy deposition data show that for propylene, 3 μm multiple photon excitation occurs most efficiently at the methyl group, and furthermore that efficient methyl group excitation requires the CH group on the adjacent carbon. Thus 3 μm multiple photon excitation of propylene, while involving energy deposition directly into several spatially discrete intramolecular groups, is found to be enhanced by specific intramolecular couplings. Implications of this result for mechanisms of IR multiple photon excitation are discussed.