EDP Sciences
Free access
Volume 493, Number 2, January II 2009
Page(s) 687 - 696
Section Atomic, molecular, and nuclear data
DOI http://dx.doi.org/10.1051/0004-6361:200810712
Published online 20 November 2008

A&A 493, 687-696 (2009)
DOI: 10.1051/0004-6361:200810712

Rotational excitation of formaldehyde by hydrogen molecules: ortho-H $\mathsf{_2}$CO at low temperature

N. Troscompt, A. Faure, L. Wiesenfeld, C. Ceccarelli, and P. Valiron

Laboratoire d'Astrophysique de Grenoble, UMR 5571-CNRS, Université Joseph Fourier, Grenoble, France
    e-mail: afaure@obs.ujf-grenoble.fr

Received 30 July 2008 / Accepted 15 October 2008

Aims. Rate coefficients for the rotational excitation of the ten lowest levels of ortho- ${\rm H_2CO}$ by collisions with H2 molecules are computed for kinetic temperatures in the range 5-100 K.
Methods. Cross sections are obtained from extensive, fully converged, quantum-mechanical scattering calculations using a highly accurate potential energy surface computed at the CCSD(T) level with a basis set extrapolation procedure. Scattering calculations are carried out for H2 molecules in both para and ortho rotational levels.
Results. The present rates are shown to differ significantly from those available in the literature. Moreover, the strength of propensity rules is found to depend on the para/ortho form of H2. Radiative transfer modeling also shows that the new rates have a significant impact on ${\rm H_2CO}$ emission line fluxes and that they should be adopted in any detailed radiative transfer model of ortho- ${\rm H_2CO}$ in cold environments (T $\la$ 30 K).

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

© ESO 2009