On the determination of the intramolecular potential energy surface of polyatomic molecules: Hydrogen sulfide and formaldehyde as an illustration

International audienceWe present here an approach for determining the Hamiltonian of polyatomic molecules that allows one to successfully solve the problem of potential energy surface (PES) determination via construction and diagonalization of a Hamiltonian matrix of large dimension. In the suggested approach, the Hamiltonian is very simple and can be used both for any "normal" polyatomic molecule and for any isotopic species of a molecule. Molecules with two to four equivalent X-Y bonds are considered, and for illustration of the efficiency of the suggested approach, numerical calculations are made for the three-atomic (hydrogen sulfide) and four-atomic (formaldehyde) molecules

On the 'expanded local mode' approach applied to the methane molecule: isotopic substitution CH2D2 <--- CH4

International audienceOn the basis of a compilation of the 'expanded local mode' model and the general isotopic substitution theory, sets of simple analytical relations between different spectroscopic parameters (harmonic frequencies, anharmonic coefficients, ro-vibrational coefficients, different kinds of Fermi- and Coriolis-type interaction parameters) of the CH2D2 molecule are derived. All of them are expressed as simple functions of a few initial spectroscopic parameters of the mother, CH4, molecule. Test calculations with the derived isotopic relations show that, in spite of a total absence of initial information about the CH2D2 species, the numerical results of the calculations have a very good correlation both with experimental data, and results of ab initio calculations

On the "expanded local mode" approach applied to the methane molecule

Methane (CH4 ) is one of the main prototypical hydrocarbons and is of great importance in a variety of applications ranging from our understanding of the chemical bonding, structure and quantum dynamics, reaction kinetics to geology, astrophysics, atmospheric and environmental science. On that reason, during more than five last decades both the vibrational and ro-vibrational spectra of methane were a subject of numerous studies (see, for example, M.Hippler and M.Quack, J. Chem. Phys. 116 (2002) 6045. and H.M.Niederer, S.Albert, S.Bauerecker, V.Boudon, J.P.Champion and M.Quack, Chimia 62 (2008) 273 where extensive references to spectroscopic and theoretical works can be found, the complete, very long list being not reproduce here)

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)

High resolution study of the lowest inversion–vibration bands of 15NHD2: Interacting bands ν5/ν6/2ν2

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