On the determination of the intramolecular potential functions for a polyatomic molecule : H2S

International audienceOne of the most important problems of modern molecular physics connected with the study of vibrational-rotational spectra of molecules is the problem of determining the intramolecular potential function (IMPF) of molecules. This problem is important primarily because the knowledge of the potential function is the key point for a solution of the Schrödinger equation

Oб определении внутримолекулярной потенциальной функции многоатомной молекулы H2S

In modern molecular physics, there are two basic methods of determining the intramolecular potential function of polyatomic molecules. The first method is ab initio calculations and the second is the so-called semi-empirical method in which the Hamiltonian parameters are varied by direct construction of the Hamiltonian matrix. In the present work, the second approach is discussed on the example of the XY2 three-atomic molecule of the C2v symmetry. On the one hand, it is extremely simple for implementation, and on the other hand, it considerably extends the capability of application of the traditional semi-empirical methods. The approach suggested involves two aspects that make it advantageous in comparison with traditional approaches: a) the developed calculation scheme of diagonalization of matrices of huge dimensions and b) introduction of such vibrational coordinates that allow both the kinetic part of the Hamiltonian and the potential function to be expressed in a very simple form

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)

Analysis of high excited "hot" bands of the SO2 molecule

The main goal of the present study is to analyse rotational structures of highly excited "hot" vibrational bands, v1+2v2-v2 and 2v2+v3-v2, v2+3v3-v2 and 2v1+v2+v3-v2, and v2+2v3-v2. All of these bands are located in the region of considerably stronger bands, v1 + v2 and v2 + v3, 3v3 and 2v1+v3, and 2v3, respectively . On that reason, as the first step of analysis, we made assignments of transitions belonging to these strong bands. As the result of analysis, we were able to assign three times more transitions to the bands v1 + v2 , v2 + v3, and 3v3 (3360 transitions with Jmax. = 78 and Kmax.a = 27 to the band v1 + v2, and 2380 transitions with Jmax. = 69 and Kmax.a = 24 to the band v2 + v3, and about 2200 transitions with Jmax. = 60 and Kmax.a = 19 to the band 3v3) and four times more transitions to the 2v1+v3 and 2v3bands (about 2300 transitions with Jmax. = 69 and Kmax.a = 20 to the band 2v1+v3 and more than 4500 transitions with Jmax. = 76 and Kmax.a = 26 to the band 2v3) than it was known in the before literature. After "cleaning" the experimental spectrum from transitions belonging to the strong bands, assignment of transitions of "hot" bands was made on the basis of calculation scheme derived in Ref. [1]. As the result, 1230 transitions with Jmax. = 60 and Kmax.a = 20 were assigned to the band v1+2v2-v2, and 990 transitions with Jmax. = 59 and Kmax.a = 16 were assigned to the band 2v2+v3-v2, and 230 transitions with Jmax. = 35 and Kmax.a = 10 to the band v2+3v3-v2, and 115 transitions with Jmax. = 26 and Kmax.a = 11 to the band 2v1+v2+v3-v2, and 885 transitions with Jmax. = 32 and Kmax.a = 17 to the band v2+2v3-v2. The set of spectroscopic parameters, determined from the fit of all the obtained energy levels, reproduces experimental line positions with the accuracy close to experimental uncertainties. Obtained results can be used in different both pure scientific, and applied problems of physics, chemistry, astrophysics, etc. [1]. O. N. Ulenikov, E. S. Bekhtereva, O. V. Gromova, S. Alanko, V.-M. Horneman, and C. Leroy, Molec. Phys., 108, 1253, (2010)

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

International audienc