EDP Sciences
Free access
Volume 472, Number 3, September IV 2007
Page(s) 1029 - 1035
Section Atomic, molecular, and nuclear data
DOI http://dx.doi.org/10.1051/0004-6361:20077678

A&A 472, 1029-1035 (2007)
DOI: 10.1051/0004-6361:20077678

Quasi-classical rate coefficient calculations for the rotational (de)excitation of H2O by H2

A. Faure1, N. Crimier1, C. Ceccarelli1, P. Valiron1, L. Wiesenfeld1, and M. L. Dubernet2

1  Laboratoire d'Astrophysique, UMR 5571 CNRS, Université Joseph-Fourier, BP 53, 38041 Grenoble Cedex 09, France
    e-mail: afaure@obs.ujf-grenoble.fr
2  Observatoire de Paris-Meudon, LERMA UMR 8112 CNRS, 5 place Jules Janssen, 92195 Meudon Cedex, France

(Received 19 April 2007 / Accepted 4 June 2007)

Context.The interpretation of water line emission from existing observations and future HIFI/Herschel data requires a detailed knowledge of collisional rate coefficients. Among all relevant collisional mechanisms, the rotational (de)excitation of H2O by H2 molecules is the process of most interest in interstellar space.
Aims.To determine rate coefficients for rotational de-excitation among the lowest 45 para and 45 ortho rotational levels of H2O colliding with both para and ortho-H2 in the temperature range 20-2000 K.
Methods.Rate coefficients are calculated on a recent high-accuracy H2O-H2 potential energy surface using quasi-classical trajectory calculations. Trajectories are sampled by a canonical Monte-Carlo procedure. H2 molecules are assumed to be rotationally thermalized at the kinetic temperature.
Results.By comparison with quantum calculations available for low lying levels, classical rates are found to be accurate within a factor of 1-3 for the dominant transitions, that is those with rates larger than a few 10-12 cm3 s-1. Large velocity gradient modelling shows that the new rates have a significant impact on emission line fluxes and that they should be adopted in any detailed population model of water in warm and hot environments.

Key words: molecular data -- molecular processes -- ISM: molecules

© ESO 2007

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.