A model of the chemistry in hot molecular cores

We present a detailed time-dependent chemical model which has been developed to describe the chemical composition of hot molecular cores in dense star-forming interstellar clouds. We follow the chemical evolution of a cold collapsing clump of gas, including the accretion and subsequent reaction of material on to the surface of interstellar grains, until the density of molecular hydrogen in the clump becomes equal to 10⁷cm⁻³. At this point we halt the collapse and assume that some heating event, perhaps associated with the formation of a nearby star, liberates the molecular mantles back into the gas phase. Comparison between our calculated abundances and those observed in the Orion Hot Core shows that such a model is likely to be qualitatively correct. In particular, the evidence that both hydrogenation and deuteration occur on the grain surface is very strong.