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Title: Polyad quantum numbers and multiple resonances in anharmonic vibrational studies of polyatomic molecules

Abstract

In the theory of anharmonic vibrations of a polyatomic molecule, mixing the zero-order vibrational states due to cubic, quartic and higher-order terms in the potential energy expansion leads to the appearance of more-or-less isolated blocks of states (also called polyads), connected through multiple resonances. Such polyads of states can be characterized by a common secondary integer quantum number. This polyad quantum number is defined as a linear combination of the zero-order vibrational quantum numbers, attributed to normal modes, multiplied by non-negative integer polyad coefficients, which are subject to definition for any particular molecule. According to Kellman's method [J. Chem. Phys. 93, 6630 (1990)], the corresponding formalism can be conveniently described using vector algebra. In the present work, a systematic consideration of polyad quantum numbers is given in the framework of the canonical Van Vleck perturbation theory (CVPT) and its numerical-analytic operator implementation for reducing the Hamiltonian to the quasi-diagonal form, earlier developed by the authors. It is shown that CVPT provides a convenient method for the systematic identification of essential resonances and the definition of a polyad quantum number. The method presented is generally suitable for molecules of significant size and complexity, as illustrated by several examples of molecules upmore » to six atoms. The polyad quantum number technique is very useful for assembling comprehensive basis sets for the matrix representation of the Hamiltonian after removal of all non-resonance terms by CVPT. In addition, the classification of anharmonic energy levels according to their polyad quantum numbers provides an additional means for the interpretation of observed vibrational spectra.« less

Authors:
;  [1]
  1. Chemistry Department, Lomonosov Moscow State University, Moscow 119991 (Russian Federation)
Publication Date:
OSTI Identifier:
22224087
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 139; Journal Issue: 18; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; HAMILTONIANS; PERTURBATION THEORY; QUANTUM NUMBERS; RESONANCE; VIBRATIONAL STATES

Citation Formats

Krasnoshchekov, Sergey V., and Stepanov, Nikolay F. Polyad quantum numbers and multiple resonances in anharmonic vibrational studies of polyatomic molecules. United States: N. p., 2013. Web. doi:10.1063/1.4829143.
Krasnoshchekov, Sergey V., & Stepanov, Nikolay F. Polyad quantum numbers and multiple resonances in anharmonic vibrational studies of polyatomic molecules. United States. https://doi.org/10.1063/1.4829143
Krasnoshchekov, Sergey V., and Stepanov, Nikolay F. 2013. "Polyad quantum numbers and multiple resonances in anharmonic vibrational studies of polyatomic molecules". United States. https://doi.org/10.1063/1.4829143.
@article{osti_22224087,
title = {Polyad quantum numbers and multiple resonances in anharmonic vibrational studies of polyatomic molecules},
author = {Krasnoshchekov, Sergey V. and Stepanov, Nikolay F.},
abstractNote = {In the theory of anharmonic vibrations of a polyatomic molecule, mixing the zero-order vibrational states due to cubic, quartic and higher-order terms in the potential energy expansion leads to the appearance of more-or-less isolated blocks of states (also called polyads), connected through multiple resonances. Such polyads of states can be characterized by a common secondary integer quantum number. This polyad quantum number is defined as a linear combination of the zero-order vibrational quantum numbers, attributed to normal modes, multiplied by non-negative integer polyad coefficients, which are subject to definition for any particular molecule. According to Kellman's method [J. Chem. Phys. 93, 6630 (1990)], the corresponding formalism can be conveniently described using vector algebra. In the present work, a systematic consideration of polyad quantum numbers is given in the framework of the canonical Van Vleck perturbation theory (CVPT) and its numerical-analytic operator implementation for reducing the Hamiltonian to the quasi-diagonal form, earlier developed by the authors. It is shown that CVPT provides a convenient method for the systematic identification of essential resonances and the definition of a polyad quantum number. The method presented is generally suitable for molecules of significant size and complexity, as illustrated by several examples of molecules up to six atoms. The polyad quantum number technique is very useful for assembling comprehensive basis sets for the matrix representation of the Hamiltonian after removal of all non-resonance terms by CVPT. In addition, the classification of anharmonic energy levels according to their polyad quantum numbers provides an additional means for the interpretation of observed vibrational spectra.},
doi = {10.1063/1.4829143},
url = {https://www.osti.gov/biblio/22224087}, journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 18,
volume = 139,
place = {United States},
year = {Thu Nov 14 00:00:00 EST 2013},
month = {Thu Nov 14 00:00:00 EST 2013}
}