Limits on HDS/H2S abundance ratios in hot molecular cores

We have searched for HDS emission in a small number of hot cores. Using observations of H34 2 S, we have derived upper limits to the [HDS]/[H2S] abundance ratio. The upper limits, which are close to 10−3 can be interpreted in two ways, depending on whether grain surface reactions contribute to the formation of H2S. If grains do not dominate, then the H2S observed is formed in hot, post-shocked gas and a ratio close to the cosmic [D]/[H] ratio is expected for [HDS]/[H2S]. This scenario is consistent with our upper limits and with the relatively low abundance ratio found for [HDO]/[H2O] in hot cores but does not seem to account for all of the molecular [D]/[H] ratios observed in hot cores. If grains do dominate the formation of H2S, then the observed upper limit to the ratio is consistent with the formation of ‘hot core ices’ at a temperature of 60–80 K, close to the temperature at which cometary ices are thought to form.