Collisional excitation of water in warm astrophysical media *
I. Rate coefficients for rovibrationally excited states
Laboratoire d'Astrophysique de Grenoble (LAOG), Université Joseph-Fourier, UMR 5571 CNRS, BP 53, 38041 Grenoble Cedex 09, France e-mail: email@example.com
2 Groupe de Recherche en Astronomie et Astrophysique du Languedoc (GRAAL), Université Montpellier II, UMR 5024 CNRS, 34095 Montpellier Cedex 05, France
Accepted: 25 September 2008
Context. The interpretation of water line emission from infrared and submillimetre observations requires a detailed knowledge of collisional rate coefficients over a wide range of levels and temperatures.
Aims. We attempt to determine rotational and rovibrational rate coefficients for H2O colliding with both H2 and electrons in warm, molecular gas.
Methods. Pure rotational rates are derived by extrapolating published data using a new method partly based on the information (phase space) theory of Levine and co-workers. Ro-vibrational rates are obtained using vibrational relaxation data available in the literature and by assuming a complete decoupling of rotation and vibration.
Results. Rate coefficients were obtained for the lowest 824 ro-vibrational levels of H2O in the temperature range 200-5000 K. Our data is expected to be accurate to within a factor of ~5 for the highest rates (10-11 cm3 s-1). Smaller rates, including the ro-vibrational ones, should be generally accurate to within an order of magnitude. As a first application of this data, we show that vibrationally excited water emission observed in evolved stars is expected to be at least partly excited by means of collisions.
Key words: molecular data / molecular processes / ISM: molecules
© ESO, 2008