  The abundances of deuterated molecules with respect to their main
isotopologue counterparts have been determined to be orders of magnitude higher
than expected from the cosmic abundance of deuterium relative to hydrogen. The
increasing number of singly and multi-deuterated species detections helps us to
constrain the interplay between gas-phase and solid-state chemistry and to
understand better deuterium fractionation in the early stages of star
formation. Acetaldehyde is one of the most abundant complex organic molecules
(COMs) in star-forming regions and its singly deuterated isotopologues have
already been observed towards protostars. A spectroscopic catalogue for
astrophysical purposes is built for doubly deuterated acetaldehyde CHD2CHO from
measurements in the laboratory. Submillimetre wave transitions were measured
for the non-rigid doubly deuterated acetaldehyde CHD2CHO displaying hindered
internal rotation of its asymmetrical CHD2 methyl group. A line position
analysis is carried out allowing us to reproduce 853 transition frequencies
with a weighted root mean square standard deviation of 1.7, varying 40
spectroscopic constants. A spectroscopic catalogue for astrophysical purposes
is built from the analysis results. Using this catalogue we were able to detect
for the first time CHD2CHO towards the low-mass protostellar system IRAS
16293-2422 utilizing data from the ALMA Protostellar Interferometric Line
Survey. The first detection of the CHD2CHO species allows for the derivation of
its column density with a value of 1.3x10^15 cm^-2 and an uncertainty of
10-20%. The resulting D2/D ratio of ~20% is found to be coincident with D2/D
ratios derived for other complex organic molecules towards IRAS~16293-2422,
pointing at a common formation environment with enhanced deuterium
fractionation.
