EDP Sciences
Free access
Volume 391, Number 2, August IV 2002
Page(s) 681 - 687
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20020825

A&A 391, 681-687 (2002)
DOI: 10.1051/0004-6361:20020825

Dark cloud chemistry in initially H-rich regions

J. M. C. Rawlings1, T. W. Hartquist2, D. A. Williams1 and S. A. E. G. Falle3

1  Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, England
2  Department of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, England
3  Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, England

(Received 12 March 2002 / Accepted 2 June 2002 )

The chemistry in dark regions of dense cores is explored as a function of the initial abundance ratio of H to H 2, on the assumption that some cores form on a timescale and are younger than the time required for the H :H 2 ratio to attain its equilibrium value. Observational diagnostics of non-equilibrium values of the initial H :H 2 ratio are identified. In initially H-rich material, the abundances of OH, NH 3, CN, and HNC are for some time higher than they are in initially H-poor material. In initially H-poor regions, the abundances of CO, species containing multiple carbon atoms in each molecule, and CS are larger for an (observationally significant) period than in initially H-rich material.

Key words: ISM: clouds -- ISM: molecules -- astrochemistry -- molecular processes

Offprint request: J. M. C. Rawlings, jcr@star.ucl.ac.uk

© ESO 2002