5314027770

POSTER SESSION. H25

SITE SYMMETRY AND EFFECTIVE HAMILTONIANS FOR H₂X MOLECULES IN THE LOCAL MODĘ LIMIT

V.M. MIKHAILOY, O.V. NAUMENKO, M.A. SMIRNOY. Insti-tute of Atmospheric Optics, SB RAS. Tomsk, Russta. 634055.

The quasidegeneracy of stretching vibration frequencies u>i and is known to tako place in H₂X molecules. The cj\ - uą difference has a trend to decrea.se as the mass m\ of central atom incrcased. Even at the lowest values of rotational quantuin nuinbers the rotational sublevels of (100) and (001) local modę pair are strongly perturbed by Coriolis-type interaction.

In the contribution the principal symmetry asperts are considered in view of construction of effectivc rotational Hamiltonians for quasidegenerate vibrational stat.es of molecules in interest. It has been shown that in the local modę limit the effcctive Hamiltonian for rotational dependence of Coriolis-type accidental resonance don’t depend on the ordering schernes of the terms in the expansion of the initial Hamiltonian similar to the case of the effective Hamiltonian for the isolated vibrational State.

The site symmetry of the effective Hamiltonian for the stretching modes of H>X molecules at the condition mu m\ is reduced to Cs symmetry as compared with C₂y symmetry of the initial Hamiltonian. The analysis of dynamie symmetry rcduction and the local modę pairs energy spectra structure has been donc for nonlinear H₂X molecules and their deuterated rnodification HDX. The admissible applications of represented approach to theories of mean square vibration amplitudes and MW and IR linę intensitics are discussed for molecules in interest. The effective Hamiltonian representations in various vibrational coordinates are also discussed for the case under consideration.

The symmetry rcduction efTects of the effective Hamiltonian following from the hypothe-sis of frozen central atom motion have been illustrated on the H₂S molecule IR-spectra identification.