Isotopic shift of vibrational energy levels of molecules: H2S isotopologues
A.D. Bykov, B.A. Voronin
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
Keywords: H2S, hydrogen sulfide, isotopic shift, vibrational level, perturbation theory, Padé-Hermite approximants
Abstract
Determining the isotopic shift of vibrational energy levels of molecules is a challenging task in molecular spectroscopy. Detailed knowledge of the vibrational-rotational energy spectrum is necessary, for example, for laser isotope separation. In this paper, a calculation method based on high-order perturbation theory and summation of series by the method of quadratic Padé-Hermite approximants is proposed. The method is applied to determine the isotopic shifts of vibrational energy levels of all stable hydrogen sulfide isotopologues. Calculations were performed using ab initio intramolecular potential function within a simple quartic force field model. To refine the results, corrections were introduced to account for the error in ab initio data. The results of summation of perturbation theory series coincide with the levels determined by the variational method with accuracy of 10-10-10-2 cm-1. The corrections reduced the root-mean-square error in the available experimental level values to 3.5 cm-1 (0.3%).
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