Numerical-Analytic Implementation of the Higher-Order Canonical Van Vleck Perturbation Theory for the Interpretation of Medium-Sized Molecule Vibrational Spectra

Krasnoshchekov, S.V.; Isayeva, E.V.; Stepanov, N.F.

Авторы: Krasnoshchekov Sergey V., Isayeva Elena V., Stepanov Nikolay F.
Журнал: The Journal of Physical Chemistry A: Molecules, Clusters, and Aerosols
Том: 116
Номер: 14
Год издания: 2012
Издательство: American Chemical Society
Местоположение издательства: United States
Первая страница: 3691
Последняя страница: 3709
DOI: 10.1021/jp211400w
Аннотация: Anharmonic vibrational states of semirigid polyatomic molecules are often studied using the second-order vibrational perturbation theory (VPT2). For efficient higher-order analysis, an approach based on the canonical Van Vleck perturbation theory (CVPT), the Watson Hamiltonian and operators of creation and annihilation of vibrational quanta is employed. This method allows analysis of the convergence of perturbation theory and solves a number of theoretical problems of VPT2, e.g., yields anharmonic constants y(ijk) Z(ijk1),and allows the reliable evaluation of vibrational IR and Raman anharmonic intensities in the presence of resonances. Darling-Dennison and higher-order resonance coupling coefficients can be reliably evaluated as well. The method is illustrated on classic molecules: water and formaldehyde. A number of theoretical conclusions results, including the necessity of using sextic force field in the fourth order (CVPT4) and the nearly vanishing CVPT4 contributions for bending and wagging modes. The coefficients of perturbative Dunham-type Hamiltonians in high-orders of CVPT are found to conform to the rules of equality at different orders as earlier proven analytically for diatomic molecules. The method can serve as a good substitution of the more traditional VPT2.
Добавил в систему: Краснощеков Сергей Вадимович

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Numerical-Analytic Implementation of the Higher-Order Canonical Van Vleck Perturbation Theory for the Interpretation of Medium-Sized Molecule Vibrational Spectraстатья

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