The importance of new rate coefficients for deuterium fractionation reactions in interstellar chemistry

Rate coefficients for deuterium fractionation reactions that are important at low temperatures have recently been studied at 10 K in the laboratory for the first time. In this paper, we incorporate these newly measured rates, or values based on them, into existing models of gas-phase interstellar deuterium chemistry. We then compare our results with those obtained previously and with observations of deuterated molecules in dark clouds, specifically TMC-1, L134N and L1544. In general, the new rates tend to reduce the amount of fractionation that can occur in the gas, which may present problems in regions where high molecular deuterium/hydrogen ratios have been observed.