Fourfold Clusters of Rovibrational Energy Levels for H 2S Studied with a Potential Energy Surface Derived from Experiment

Abstract

We report here an optimization of the parameters in an analytical representation of the potential energy function for the electronic ground state of hydrogen sulfide H25 on the basis of experimental data. The calculations are earned out with the MORBID (Morse Oscillator Rigid Render Internal Dynamics) computer program (P. Jensen, J. Mol. Spectrosc. 128, 478-501, 1988; J. Chem. Soc. Faraday Trans. 284, 1315-1340, 1988; in "Methods in Computational Molecular Physics" (S. Wilson and G. H. F. Diercksen. Eds.), Plenum, New York, 1992). In the least-squares fitting, we adjusted 14 parameters to fit a total of 548 rotation-vibration energy spacings involving J ≤ 5 for the four isotopic molecules H 2 32S, D 2 32S, HD 32S, and H 2 34S. The data were reproduced with root-mean-square deviations of 0.134 cm −1 for the rotational energy spacings and 0.422 cm −1 for the vibrational spacings. We have used the fitted potential energy* surface as the starting point for a theoretical investigation of the nearly degenerate, four-member groups of energy levels formed in the rotation-vibration energy spectrum of H 2S. Toward this end, we have calculated the rovibrational energy levels in the vibrational ground state, the ν 2 vibrational state, and the ν 1/ν 3/2ν 2 interacting vibrational states of H 2 32S for J ≤ 40. The rotational energy level patterns obtained for these vibrational states of H 2 32S are very similar in structure to those calculated previously for H 2 80Se (P. Jensen and I. N. Kozin. J. Mol. Spectrosc. 160, 39-57, 1993; I. N. Kozin and P. Jensen, J. Mol. Spectrosc. 161, 186-207, 1993), although there is some difference in detail.