Rotational excitation of 20 levels of para-H2O by ortho-H2 (j2 = 1, 3, 5, 7) at high temperature
F. Daniel1, M.-L. Dubernet2,3, F. Pacaud2 and A. Grosjean4
Departamento Molecular and Infrared Astrophysics, Consejo Superior de Investigaciones
Cientificas, C/ Serrano 121, 28006 Madrid, Spain
2 Université Pierre et Marie Curie, LPMAA UMR CNRS 7092, Case 76, 4 Place Jussieu, 75252 Paris Cedex 05, France e-mail: email@example.com
3 Observatoire de Paris, LUTH UMR CNRS 8102, 5 Place Janssen, 92195 Meudon, France
4 Institut UTINAM, UMR CNRS 6213, 41 bis avenue de l'Observatoire, BP 1615, 25010 Besançon Cedex, France
Accepted: 16 February 2010
Aims. The objective is to obtain the best possible set of rotational (de)-excitation state-to-state and effective rate coefficients for temperatures up to 1500 K. State-to-state rate coefficients are presented among the 20 lowest levels of para-H2O with H2(j2 = 1) and Δj2 = 0, + 2, and among the 10 lowest levels of para-H2O with H2(j2 = 3) and Δj2 = 0, -2.
Methods. Calculations are performed with the close coupling (CC) method over the whole energy range, using the same 5D potential energy surface (PES) as the one employed in our latest publications on water. We compare our CC results both with thermalized quasi-classical trajectory (QCT) calculations using the same PES and with previous quantum calculations obtained between T = 20 K and T = 140 K with a different PES.
Results. Comparisons with thermalized QCT calculations show factors from 1 to 3. Until recently the only other available set of rate coefficients were scaled collisional rate coefficients obtained with He as a collision partner, and differences between CC and scaled results are shown to be greater than with QCT calculations. The use of the CC accurate sets of rate coefficients might lead to re-estimation of water abundance in the astrophysical whenever models include the scaled H2O–He rate coefficients.
Key words: molecular data / molecular processes / ISM : molecules
© ESO, 2010