2002A&A...391..681R

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.