GROUP-THEORETICAL TREATMENT OF SELECTION RULES FOR VIBRATIONAL TRANSITIONS IN MOLECULES EXHIBITING LARGE AMPLITUDE TUNNELING MOTIONS
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Date
1989
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Ohio State University
Abstract
As pointed out qualitatively by a number of authors, and as discussed quantitatively recently by Fraser1, tunneling splittings may be significantly changed in excited vibrational states of van der Waals complexes when the tunneling motion necessitates transfer of vibrational excitation from one monomer to the other. For this and other reasons there is at present considerable interest in studies of vibrational transitions in such complexes and other molecules exhibiting tunneling motions. In the present paper we examine from a group theoretical point of view methods for determining selection rules for transitions among the various tunneling-rotational components of the ground and excited vibrational states involved in such studies. For certain cases, which correspond physically to those where vibrational excitation need not be transferred, unambiguous group theoretical predictions, based on rather simple considerations, can be made for the selection rules. For other cases, where vibrational excitation must be transferred from one part of the molecule to another, the simple considerations mentioned above break down, and several different group theoretical ``predictions'' emerge, based on assumptions concerning the signs of the coupling matrix elements leading to the intramolecular energy transfer. These theoretical ideas will be illustrated for molecules like $N_{2}H_{4}, CH_{3}NH_{2}, (HCCH)_{2}$ and $(H_{2}O)_{2}$.
Description
$^{1}$G. T. Fraser, J. Chem. Phys. in press.
Author Institution: Molecular Spectroscopy Division, National Institute for Standards and Technology
Author Institution: Molecular Spectroscopy Division, National Institute for Standards and Technology