A "KEYHOLE" MODEL OF IVR TO ACCOUNT FOR THE CONTRASTING EIGENSTATE-RESOLVED INFRARED SPECTRA OF 1-BUTYNE AND ETHANOL

$^{1}$ A. M. de Souza, D. Kaur, and D. S. Perry. J. Chem. Phys. 88, 4659 (1988). $^{2}$ A. Mcllroy, and D. J. Nesbitt, J. Chem. Phys. 92, 2229 (1990).Author Institution: Department of Chemistry, University of AkronRecent molecular eigenstate-resolved infrared spectra 1-butyne1-2 and ethanol have given insight into the nature of the couplings responsible for intramolecular vibrational redistribution (IVR) at low energies. In the alkynyl C-II band of 1-butyne, the pattern of the coupling is independent of molecular rotation and is therefore attributed to anharmoic vibrational interactions. In contrast, strong rotational affects are observed in the methyl stretching region of ethanol indicating a Coriolis and/or centrifugal coupling mechanism. The present data on the methyl region of 1-butyne does not exhibit this kind of dramatic rotational effect. Despite the apparent difference in coupling mechanism, the interaction widths and average matrix elements are of similar size in both moleculcs. A ``keyhole'' model of IVR will be presented in order to account for the similarities and difference between the two molecules. According to the model, the primary coupling between the zero-order C-H stretch and the bath is similar for both molecules. i. e. anharmonic in nature. The difference between the molecules lies in way bath states couple to each other. In 1-butyne, the bath-bath coupling is mainly anharmonic in nature but in ethanol Coriolis and/or anharmonic coupling among the bath states is also active. Therefore in ethanol, $K_{\prime}$ and $K_{\prime}$ are no longer good quantum numbers and it is possible for IVR to explore the whole of rotational-vibrational phase space