HERMAN-WALLIS EFFECTS IN THE OVERTONE SPECTRUM OF HCN
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Publisher:Ohio State University
In our investigations of the visible overtone spectrum of HCN, using the technique of cavity ring down spectroscopy, we have found perpendicular transitions (which are much weaker than nearby parallel transitions) show systematic Herman-Wallis effects, with the R branch being enhanced and the P branch decreased in intensity compared to the line strengths predicted by the Honl-London factors. Recent work by Maki and Quapp on the near-IR spectrum has also found Herman-Wallis effects in a large number of bands. We have developed a theory for the effect, based upon a mixed variational and perturbative treatments. Anharmonicity is treated by diagonalizing the vibrational Hamiltonian in a large basis set of vibrational functions made up of products Morse oscillator functions for the stretching modes and harmonic oscillator functions for the bending mode. Rovibronic interactions are treated to second order in perturbation theory. In this treatment, Herman-Wallis effects arise from both Coriolis interactions in both first and second order and from centrifugal distortion in first order. We have done calculations using the empirical potential energy surface of Carter, Handy, and Mills, and the ab initio electric dipole function calculated by Botschwina and co-workers.
Author Institution: Princeton University, Princeton, NJ 08544
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