Collisional excitation of water in warm astrophysical media I. Rate coefficients for rovibrationally excited states

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 H(2)O colliding with both H(2) 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 H(2)O in the temperature range 200-5000 K. Our data is expected to be accurate to within a factor of similar to 5 for the highest rates (greater than or similar to 10(-11) cm(3) s(-1)). Smaller rates, including the rovibrational 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.