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Ab initio calculations of the Raman intensities of fundamental vibrations of polyatomic molecules using the improved virtual orbital technique

par Raeymaekers, Paul ;Figeys, Hubert ;Geerlings, Pau̧l
Référence Journal of molecular structure. Theochem, 169, C, page (509-530)
Publication Publié, 1988-08

Article révisé par les pairs

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Résumé :

The SOS-IVO method previously successfully applied to the calculation of molecular dipole polarizabilities at equilibrium geometry is used, in conjunction with the finite difference approach for the evaluation of polarizability derivatives, to calculate scattering coefficients and depolarization ratios of vibrational Raman bands. A large basis set, based on Dunning's double and triple zeta s-p basis, is used in which polarization and diffuse functions are introduced ([DTZ/DPP]). Use is also made, in view of its success in equilibrium polarizability calculations, of a reduced basis ([DTZ/DP]) in which only a limited number of polarization functions, simulated by spherical Gaussian orbitals, are included based on symmetry considerations about the polarizability tensor components. The theory is applied to a series of molecules belonging to the C2v (H2O, H2CO), C3v (NH3, CH3CN), C∞v and D∞h (HF and N2) point groups, for which experimental gas phase intensity data are available and for which, in most cases, calculations using more demanding methods (finite field perturbation theory, analytical gradient method) were already available in the literature. Except for shortcomings in the cases of vibrational modes involving the elongation of a triple bond, a satisfactory agreement between theoretical and experimental intensities is obtained, indicating an average deviation factor of about 1.4 between theoretical and experimental polarizability derivative tensor components. The reduced basis performs well, except in the case of some very weak bending modes where recently an extremely high basis set sensitivity has been noticed. © 1988.