The effect of an increased elemental D/H ratio on deuterium fractionation in the cold interstellar medium

Measurements using the Far Ultraviolet Spectroscopic Explorer (FUSE) show that the gas-phase D/H ratio in the solar neighborhood is highly variable and suggest that the elemental abundance of deuterium in the Galactic disk may be higher than previously thought. We investigate in this Letter the possible consequences of such an enhanced D/H ratio on the deuterium fractionation in singly and multiply deuterated molecules in cold, dense gas. We show that a modest increase in the elemental abundance of deuterium can lead to significant enhancements in abundances of multiply deuterated species.