Rotational excitation of SO by He at low temperature

Details Rotational excitation of SO by He at low temperature Rotational excitation of SO by He at low temperature

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sf2a.conf..499l&link_type=abstract

SF2A-2004: Semaine de l'Astrophysique Francaise, meeting held in Paris, France, June 14-18, 2004. Edited by F. Combes, D. Barret

Astronomy and Astrophysics

Astrophysics

Scientific paper

In the next five years, Herschel and ALMA will open the universe to high spatial and spectral resolution studies at infrared and submillimeter wavelengths: interpretation of the observations in terms of physical and chemical characteristics of the sources will require experimental and theoretical determination of new atomic and molecular data, in particular collisional excitation rates. In this poster, we present new results on collisional excitation of SO by He at low temperature.
In a first step, we have studied the electronic ground state of SO(X3Sigma-) and more precisely the fine structure of the rotational levels that is needed to interpret the observations. The fine structure constants being large, we calculated the eigenvalues and the eigenvectors of the effective hamiltonian, including the fine structure couplings, in order to obtain the energies of the rotational levels.
A new potential energy surface was calculated for the SO(X3Sigma-)+He system, with the RCCSD(T) method and the aug-cc-pVTZ (AVTZ) basis set, using the MOLPRO code. The collisional cross sections were calculated in a close-coupling approach, using the MOLSCAT computer program of Hutson and Green (1995) modified to treat collisions with molecules of 3Sigma- symmetry. The cross sections were obtained for energies up to 200cm-1 which allows to determine rates until 20 °K. We have shown that the recoupling approximation [Green, ApJ, 434, 188 (1994)] often used to obtain cross sections between fine structure levels from cross sections calculated without fine structure, is not valid at low temperature.

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