Rotational spectroscopy of mono-deuterated oxirane ($c$-C$_2$H$_3$DO) and its detection towards IRAS 16293$-$2422 B

TL;DR

This study reports the laboratory rotational spectrum of mono-deuterated oxirane, updates its spectroscopic parameters, and reports its first detection in the interstellar medium towards IRAS 16293-2422 B, revealing insights into deuteration processes in star-forming regions.

Contribution

The paper provides the first laboratory measurements and astrophysical detection of mono-deuterated oxirane, improving spectroscopic data and analyzing its abundance in a protostellar environment.

Findings

Detected mono-deuterated oxirane in IRAS 16293-2422 B using ALMA.

Derived a rotational temperature of approximately 103 K for the molecule.

Estimated a D-to-H ratio of about 0.036, indicating early formation in prestellar cores.

Abstract

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 $c$-C$_2$H$_3$DO 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 $T_{\rm rot} = 103 \pm 19$ K, which in turn agrees well with 125 K derived for the $c$-C$_2$H$_4$O main isotopologue previously. The $c$-C$_2$H$_3$DO to $c$-C$_2$H$_4$O ratio is found to be $\sim$0.15 corresponding to a D-to-H ratio of $\sim$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.