SIMBAD references

We present new models of interstellar deuterium chemistry that include more multiply deuterated species than previously considered. We first describe the updates that have been made, and compare the results given by two different underlying networks at the low temperatures and high densities characteristic of prestellar cores. We then use the models to explain recent observations of CO depletion and D₂CO/H₂CO ratios in prestellar cores. We find limited agreement between our models and observations for constant density scenarios, but for two of these cores we demonstrate reasonable agreement when we take the density structure of the core into account.