We prepared a sample of mono-deuterated oxirane and studied its rotational
spectrum in the laboratory between 490 GHz and 1060 GHz in order to improve its
spectroscopic parameters and consequently the calculated rest frequencies of
its rotational transitions. The updated rest frequencies were employed to
detect c-C2H3DO for the first time in the interstellar medium in the
Atacama Large Millimetre/submillimetre Array (ALMA) Protostellar
Interferometric Line Survey (PILS) of the Class 0 protostellar system IRAS
16293−2422. Fits of the detected lines using the rotation diagrams yield a
temperature of Trot=103±19 K, which in turn agrees well with 125
K derived for the c-C2H4O main isotopologue previously. The
c-C2H3DO to c-C2H4O ratio is found to be ∼0.15
corresponding to a D-to-H ratio of ∼0.036 per H atom which is slightly
higher than the D-to-H ratio of species such as methanol, formaldehyde, ketene
and but lower than those of the larger complex organic species such as ethanol,
methylformate and glycolaldehyde. This may reflect that oxirane is formed
fairly early in the evolution of the prestellar cores. The identification of
doubly deuterated oxirane isotopomers in the PILS data may be possible judged
by the amount of mono-deuterated oxirane and the observed trend that multiply
deuterated isotopologues have higher deuteration rates than their
mono-deuterated variants.Comment: 10 pages total; Mon. Not. R. Astron. Soc., accepte