Enhanced deuterium fractionation in dense interstellar cores resulting from multiply deuterated H3+

In this Letter, we present the first results from updated models of interstellar deuterium chemistry that now include all possible deuterated isotopomers of H-3(+). We find that in regions of high density and heavy depletion, such as prestellar cores, the inclusion of HD2+ and D-3(+) enhances the fractionation of ionic and neutral species significantly. Our models are the first to predict the very high atomic D/H ratios (greater than or equal to0.3) necessary for grain-surface chemistry models to reproduce the high formaldehyde and methanol fractionation seen in star-forming regions.