Millimetre and sub-millimetre spectroscopy of doubly deuterated acetaldehyde (CHD₂CHO) and first detection towards IRAS 16293-2422

Context. The abundances of deuterated molecules with respect to their main isotopologue counterparts have been determined be orders magnitude higher than expected from the cosmic abundance deuterium relative hydrogen. increasing number singly and multi-deuterated species detections helps us constrain interplay between gas-phase solid-state chemistry understand better fractionation in early stages star formation. Acetaldehyde is one most abundant complex organic (COMs) star-forming regions its isotopologues already observed towards protostars. Aims. A spectroscopic catalogue for astrophysical purposes built doubly acetaldehyde (CHD 2 CHO) measurements laboratory. With this accurate catalogue, we aim search detect interstellar medium retrieve column density abundance. Methods. Sub-millimetre wave transitions were measured non-rigid CHD CHO displaying hindered internal rotation asymmetrical CHD2 methyl group. An analysis a dataset consisting previously microwave newly ones was carried out an effective Hamiltonian which accounts tunnelling Results. line position out, allowing reproduce 853 transition frequencies weighted root mean square standard deviation 1.7, varying 40 constants. results. Using able detect, first time, low-mass proto-stellar system IRAS 16293-2422 utilising data ALMA Proto-stellar Interferometric Line Survey. Conclusions. detection allowed derivation value 1.3×10 15 cm ?2 uncertainty 10–20%. resulting D /D ratio ~20% found coincident ratios derived other COMs 16293-2422, pointing common formation environment enhanced fractionation.