Influence of a new potential energy surface on the rotational (de)excitation of HO by H at low temperature

¹ Observatoire de Paris-Meudon, LERMA UMR CNRS 8112, 5 Place Jules Janssen, 92195 Meudon Cedex, France e-mail: marie-lise.dubernet@obspm.fr
² Laboratoire d'Astrophysique, Observatoire de Besançon, UMR CNRS 6091, Université de Franche-Comté, 41 bis avenue de l'Observatoire, BP 1615, 25010 Besançon Cedex, France
³ Laboratoire d'Astrophysique, Observatoire de Grenoble, UMR CNRS 5571, Université Joseph Fourier, 38041 Grenoble Cedex 09, France
⁴ Department of Physical and Theoretical Chemistry, Faculty of Natural Sciences, Comenius University, Mlynska dolina CH1, 84215 Bratislava, Slovakia
⁵ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

Received: 12 June 2006
Accepted: 2 August 2006

Abstract

Aims.Using a newly determined 5D potential energy surface for H₂–H₂O we provide an extended and revised set of rate coefficients for de-excitation of the lowest 10 para- and 10 ortho- rotational levels of H₂O by collisions with para- and ortho-H₂, for kinetic temperatures from 5 K to 20 K.

Methods.Our close coupling scattering calculations involve a slightly improved set of coupled channels with respect to previous calculations. In addition, we discuss the influence of several features of this new 5D interaction on the rotational excitation cross sections.

Results. The new interaction potential leads to significantly different rate coefficients for collisions with para-H₂ . In particular the de-excitation rate coefficient for the 1₁₀ to 1₀₁ transition is increased by up to 300% at 5 K. At 20 K this increase is 75%. Rate coefficients for collisions with ortho-H₂ are modified to a lesser extent, by up to 40%. The influence of the new potential on collisions with both para- and ortho-H₂ is expected to become less pronounced at higher temperatures.