SIMBAD references

Deuterium chemistry in the interstellar medium has drawn a growing attention in the past few years with the discovery of large abundances of the multiply (doubly and triply) deuterated molecules towards star forming regions. According to chemical models, high fractionation can only be achieved when the gas-phase is cold and depleted of species like CO and O. We recently detected D₂CO, the doubly deuterated form of formaldehyde towards a sample of pre-stellar cores and found [D₂CO]/[H₂CO] ratios around 1-10, similar to the ratio measured in protostars, thus confirming the pre-stellar origin of deuterium in formaldehyde. We also detected for the first time in a pre-stellar core H₂D⁺, a fundamental ion in the deuteration process. The deuterium fractionation correlates with the CO depletion in the cores, however the measured D₂CO/H₂CO ratio and H₂D⁺ abundance exceed the predictions of theoretical models by an order of magnitude. The search for H₂D⁺ in more sources is needed to get at a better understanding of deuteration processes, as well as the search for D₂H⁺, which has been proposed to be one of the missing ingredients of chemical models.