Investigation of Coriolis Mixing in Benzene

Author: Runnels, John Hulett

Year: 1983

Degree: Master's thesis

Advisor: Marcus, Rudolph A.

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/yxqj-6804

Abstract

An explanation for some recent observations in the electronic absorption spectrum of benzene by Schlag and coworkers is proposed. Several vibrational lines of the S_0 to S_1 transition have been studied by these authors with the Doppler—free, two—photon technique developed earlier. The resolution of this technique is so high that individual Δ J=0, Δ K=0 rotational lines in the Q—branch of a given vibrational transition may be seen in the electronic absorption spectrum. A major progression in the two—photon spectrum is the 14^1_0 1^n_0 progression. It was found that the 14^1_0 1^0_0 and 14^1_0 1^1_0 transitions had well—resolved rotationalstructure, but the 14^1_0 1^2_0 transition had reduced, not well resolved rotational structure--except for the prominent K=0 lines for small to medium values of J. This suggested to us Coriolis mixing. The model presented here utilizes a suggestion of Riedle et al.The Coriolis coupling to neighboring vibrational states is followed by a rapid radiationless depletion of these states, consistent with the decreased fluorescence yield observed by Wunsch et al. Estimates are made of the density of states of the various symmetries; these estimates are then used to estimate the extent of the relevant Coriolis mixing. The model results in a large decrease in intensity of non—zero K lines relative to the K=0 lines for the 14^1_0 1^2_0 transition, but not for the 14^1_0 1^0_0 and 14^1_0 1^1_0 transitions, in agreement with the experimental observations, making a few assumptions discussed below, but without the use of adjustable parameters. Predictions are then made for the rotational structure of other strong transitions in the two—photon spectrum of benzene.

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