In a previous article we have introduced an alternative perturbation scheme to the traditional one starting from the harmonic oscillator, rigid rotator Hamiltonian, to find approximate solutions of the spectral problem for rotation-vibration molecular Hamiltonians. The convergence of our method for the methane vibrational ground state rotational energy levels was quicker than that of the traditional method, as expected, and our predictions were quantitative. In this second article, we study the convergence of the ab initio calculation of effective dipole moments for methane within the same theoretical frame. The first order of perturbation when applied to the electric dipole moment operator of a spherical top gives the expression used in previous spectroscopic studies. Higher orders of perturbation give corrections corresponding to higher centrifugal distortion contributions and are calculated accurately for the first time. Two potential energy surfaces of the literature have been used for solving the anharmonic vibrational problem by means of the vibrational mean field configuration interaction approach. Two corresponding dipole moment surfaces were calculated in this work at a high level of theory. The predicted intensities agree better with recent experimental values than their empirical fit. This suggests that our ab initio dipole moment surface and effective dipole moment operator are both highly accurate.
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7 May 2012
Research Article|
May 04 2012
Ab initio calculation of the rotational spectrum of methane vibrational ground state
P. Cassam-Chenaï;
P. Cassam-Chenaï
a)
1Laboratoire J. A. Dieudonné, UMR 6621 du CNRS,
Faculté des Sciences
, Parc Valrose, 06108 Nice Cedex 2, France
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J. Liévin
J. Liévin
2
Université Libre de Bruxelles
, Service de Chimie quantique et Photophysique, CP 160/09, 50 Av. F.D. Roosevelt, B-1050 Bruxelles, Belgium
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a)
Electronic mail: cassam@unice.fr.
J. Chem. Phys. 136, 174309 (2012)
Article history
Received:
December 20 2011
Accepted:
April 06 2012
Citation
P. Cassam-Chenaï, J. Liévin; Ab initio calculation of the rotational spectrum of methane vibrational ground state. J. Chem. Phys. 7 May 2012; 136 (17): 174309. https://doi.org/10.1063/1.4705278
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