On the 'Expanded' Local Mode Approach and Isotopic Eff ect (CH2D2/CH3D/CHD3) in the Methane Molecule

Earlier derived, [1] - [3], for the XY2 (C2v) and XY3 (C3v) molecules "expanded local mode model" is applied to the methane-type, XH4, molecules. Value of the ambiguity parameter, sin \_gamma, simple value of all transformation coefficients, l, are obtained for the CH4 molecule. It gives us possibility, on the one hand, 1). to derive simple relations between different spectroscopic parameters (harmonic frequencies, anharmonic parameters and vibrational tetrahedral coefficients, rotational-vibrational and rotational tetrahedral coefficients) of the CH4 molecule, and, on the other hand, 2). on the base of the general isotopic substitution theory (see, e:g:, [4]), to obtain very simple values of transformation l coefficients for di fferent deuterated species, CH3D, CH2D2, and CHD3, of the methane molecule. As the fi nal step, numerous isotopic relations between di fferent spectroscopic parameters of the mother molecule, CH4, and deuterated, CH3D, CH2D2, CHD3, species are derived. Comparison of the derived relations with the experimental values of spectroscopic parameters shows more than satisfactory correlation between the results. [1]. O. N. Ulenikov, R. N. Tolchenov, and Zhu Qing-Shi, Spectrochim. Acta A 52, 1829 - 1841 (1996). [2]. O. N. Ulenikov, S. N. Yurchenko, and R. N. Tolchenov, Spectrochim. Acta A 53, 329 - 334 (1997). [3]. O. N. Ulenikov, R. N. Tolchenov, and Zhu Qing-Shi, Spectrochim. Acta A 53, 845 - 853 (1997). [4]. A. D. Bykov, Yu. S. Makushkin, and O. N. Ulenikov, J. Molec. Spectrosc. 85, 462 - 479 (1981).