Rotational spectroscopy of oxirane-2,2-d2, c-CD2CH2O, and its tentative detection toward IRAS 16293-2422 B

We prepared a sample of oxirane doubly deuterated at one C atom and studied its rotational spectrum in the laboratory for the first time between 120 GHz and 1094 GHz. Accurate spectroscopic parameters up to eighth order were determined, and the calculated rest frequencies were used to identify $c$-CD${}_2$CH${}_2$O tentatively in the interstellar medium in the Atacama Large Millimeter/submillimeter Array Protostellar Interferometric Line Survey (PILS) of the Class 0 protostellar system IRAS 16293-2422. The $c$-CD${}_2$CH${}_2$O to $c$-C${}_2$H${}_4$O ratio was estimated to be $\sim$0.054 with $T_{\mathrm{rot}}=125$ K. This value translates to a D-to-H ratio of $\sim$0.16 per H atom which is higher by a factor of 4.5 than the $\sim$0.036 per H atom obtained for $c$-C${}_2$H${}_3$DO. Such increase in the degree of deuteration referenced to one H atom in multiply deuterated isotopologs compared to their singly deuterated variants have been observed commonly in recent years.