Volume 531, July 2011
|Number of page(s)||9|
|Section||Atomic, molecular, and nuclear data|
|Published online||21 June 2011|
Collisional excitation of sulfur dioxide in cold molecular clouds*
CAB. INTA-CSIC. Department of Astrophysics. Crta Torrejón km 4. Torrejón de Ardoz, Madrid, Spain
2 LERMA and UMR 8112 of CNRS, Observatoire de Paris-Meudon, 92195 Meudon Cedex, France
3 Laboratoire d’Astrophysique de Grenoble, UMR 5571-CNRS, Université Joseph Fourier, Grenoble, France
Received: 26 November 2010
Accepted: 5 April 2011
We present collisional rate coefficients for SO2 with ortho and para molecular hydrogen for the physical conditions prevailing in dark molecular clouds. Rate coefficients for the first 31 rotational levels of this species (energies up to 55 K) and for temperatures between 5 and 30 K are provided. We have found that these rate coefficients are about ten times more than those previously computed for SO2 with helium. We calculated the expected emission of the centimeter wavelength lines of SO2. We find that the transition connecting the metastable 202 level with the 111 one is in absorption against the cosmic background for a wide range of densities. The 404−313 line is found to be inverted for densities below a few 104 cm-3. We observed the 111−202 transition with the 100 m Green Bank Telescope towards some dark clouds. The line is observed, as expected, in absorption and provides an abundance of SO2 in these objects of a few 10-10. The potential use of millimeter lines of SO2 as tracers of the physical conditions of dark clouds is discussed.
Key words: molecular processes / ISM: molecules / ISM: abundances
Tables 5 and 6 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A103
© ESO, 2011
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