Non-Empirical Calculations of Reduced Quartic, Sextic, and Octic Constants of Effective Vibrational–Rotational Hamiltonians, Based on the Operator Perturbation Theory

Efremov, I.M.; Millionshchikov, D.V.; Krasnoshchekov, S.V.

Авторы: Efremov I.M., Millionshchikov D.V., Krasnoshchekov S.V.
Журнал: Russian Journal of Physical Chemistry A
Том: 98
Номер: 5
Год издания: 2024
Издательство: Pleiades Publishing, Ltd
Местоположение издательства: Road Town, United Kingdom
Первая страница: 78
Последняя страница: 88
DOI: 10.1134/S0036024424050121
Аннотация: Models based on sets of effective vibrational–rotational Hamiltonians, parameterized by a small number of spectroscopic reduced quartic, sextic, and octic constants, can conveniently describe highly complex vibrational–rotational spectra of free small-atomic molecules containing tens and hundreds of thousands of observable lines in the microwave and infrared range. These parameters are usually determined by solving inverse problems that combine interpreting a spectrum with step-by-step fitting of parameters. Quartic and sextic constants can be routinely calculated for equilibrium nuclear configurations using analytical formulas, while considerable theoretical and computational difficulties are encountered in determining vibrationally excited and octic constants. A theoretical method is proposed for calculating reduced parameters of effective Hamiltonians in the fourth and sixth orders of the operator perturbation theory, and computational algorithms are described. It is shown that in the fourth and sixth orders, the quartic and sextic constants are in better agreement with experiments, respectively. Octic constants obtained in the sixth order can be used for verification or refinement when solving the inverse problem. Theoretical results are illustrated by the example of calculating two isotopologues of the SO2 molecule.
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Non-Empirical Calculations of Reduced Quartic, Sextic, and Octic Constants of Effective Vibrational–Rotational Hamiltonians, Based on the Operator Perturbation Theoryстатья Исследовательская статья

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