Observatoire de Paris
In the ‘70s, while several groups were trying to measure various isotopic ratios in dark clouds (13C/12C, 18O/17O/16O,…), it was quickly realized that the D/H ratio of several molecules was abnormal and deuterated species were found difficult to use in radiative transfer models as surrogate tracers of their main isotopologue when the latter was optically thick. In the early ‘90s, the spin state of H2 started to be considered in chemical networks and ten years later, the full potential of the spin-state dependent deuterium chemistry started to unfold in parallel with the recognition of the important role of the unexpected D2H+ and D3+ isotopologues of hydrogenonium to explain the existence of triply deuterated species, like CD3OH and ND3. The recognition of the slow one-way deuteration of species in cold dark clouds as a potential to trace their evolution started to emerge. Deuterated species in gas phase like N2D+ or on ice, like CHxD(3-x)OH, for x = 1..3 or HxD(2-x)O, for x = 1..2, revealed themselves as potential tracers of several phases of star formation. Their presence or absence and even better their abundance profile were identified as promising tools to estimate the age of starless and protostellar clouds. In this presentation, I will review the various aspects of Deuterium chemistry and briefly address how it can be used to trace star formation, in both low- and high-mass star formation regions.