Dark cloud chemistry in initially H-rich regions

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

Corresponding author: J. M. C. Rawlings, jcr@star.ucl.ac.uk

Received: 12 March 2002
Accepted: 2 June 2002

Abstract

The chemistry in dark regions of dense cores is explored as a function of the initial abundance ratio of H to H₂, on the assumption that some cores form on a timescale and are younger than the time required for the H:H₂ ratio to attain its equilibrium value. Observational diagnostics of non-equilibrium values of the initial H:H₂ ratio are identified. In initially H-rich material, the abundances of OH, NH₃, 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.