The ring molecule oxirane, c-C2H4O, also known as ethylene oxide or oxa-cyclopropane, was detected in the prolific high-mass star-forming region Sagittarius B2(N) by
J. E. Dickens, W. M. Irvine, M. Ohishi, M. Ikeda, S. Ishikawa, A. Nummelin, and Å. Hjalmarson,
Detection of Interstellar Ethylene Oxide (//c//-C<sub>2</sub>H<sub>4</sub>O)
Astrophys. J. 489, 753–757 (1997).
The Haystack, Nobeyama, and SEST telescopes were used to detect 10 lines from the 11,1 – 00,0 near 40 GHz up to J = 8 and up to 255 GHz. Two lines were considered to be marginal detections, and one as blended. A rotational temperature of 18 K was derived.

Subsequently, the molecule was also detected in the hot core (HII) regions G 327.30–0.60 (IRAS 15492–5426), NGC 6334 IRS 1 (IRAS 17175–3544), and G 31.41+0.31 (IRAS 18449–0115) by
A. Nummelin, J. E. Dickens, P. Bergman, Å. Hjalmarson, W. M. Irvine, M. Ikeda, and M. Ohishi,
Abundances of Ethylene Oxide and Acetaldehyde in Hot Molecular Cloud Cores
Astron. Astrophys. 337, 275–286 (1998).

The molecule was also detected in three Galactic center molecular clouds which have low dust temperatures (10–20 K), even lower rotational temperatures (around 10 K), which are moderately dense (a few tenthousand molecules per cubic centimeter), but which are kinetically moderately warm (about 100 K or more). One transition (21,1 – 20,2) was detected with the 100 m GBT telescope near 25 GHz by
M. A. Requena-Torres, J. Martín-Pintado, S. Martín, and M. R. Morris,
The Galactic Center: The Largest Oxygen-bearing Organic Molecule Repository
Astrophys. J. 672, 352–360 (2008).
The column density relative to methanol is reasonable. However, since only one transition was observed, these detections should be viewed with caution.

J. M. Lykke, A. Coutens, J. K. Jørgensen, M. H. D. van der Wiel, R. T. Garrod, H. S. P. Müller, P. Bjerkeli, T. L. Bourke, H. Calcutt, M. N. Drozdovskaya, C. Favre, E. C. Fayolle, S. K. Jacobsen, K. I. Öberg, M. V. Persson, E. F. van Dishoeck, and S. F. Wampfler
reported on
The ALMA-PILS Survey: First Detections of Ethylene Oxide, Acetone and Propanal toward the Low-mass Protostar IRAS 16293–2422
Astrophys. J. 597, Art. No. A53 (2017).
This report is the first one on the detection of ethylene oxide around a low-mass protostar. The Protostellar Interferometric Line Survey (PILS) was carried out with ALMA in its Band 7 (329 – 363 GHz). A total of 20 lines were assigned to oxirane.

A. Bacmann, A. Faure, and J. Berteaud
gave an account of
Cold and Yet Complex: Detection of Ethylene Oxide in a Prestellar Core
ACS Earth Space Chem. 3, 1000 (2019).
They used the IRAM 30 m telescope to detect some lines at 3 and 2 mm toward L1689B.

H. S. P. Müller, J. K. Jørgensen, J.-C. Guillemin, F. Lewen, and S. Schlemmer
presented the
Rotational Spectroscopy of Mono-deuterated Oxirane (//c//-C<sub>2</sub>H<sub>3</sub>DO) and Its Detection Towards IRAS 16293−2422 B
Mon. Not. R. Astron. Soc. 518, 185 (2023).
17 lines, corresponging to 19 transitions with 4 ≤ J ≤ 13 with diverse values of Ka and Kc, were identified in the PILS (Protostellar Interferometric Line Survey) data obtained with ALMA in its Band 7 (329 – 363 GHz). The c-C2H3DO to c-C2H4O ratio is ~0.15, which corresponds to a D-to-H ratio of ∼0.036 per H atom.

H. S. P. Müller, J. K. Jørgensen, J.-C. Guillemin, F. Lewen, and S. Schlemmer
presented more recently the
Rotational Spectroscopy of Oxirane-//2,2-d//<sub>2</sub> (//c//-CD<sub>2</sub>CH<sub>2</sub>O) and Its Tentative Detection Toward IRAS 16293−2422 B
J. Mol. Spectrosc. 394, Art. No. 111777 (2023).
As in the case of the mono-deuterated oxirane above, lines were identifies in the PILS data. Five or six lines are essentially unblended and have a sufficient signal-to-noise ratio, two more lines are blended, and the combination of the contributions account nicely for the emission lines. So the identification was deemed to be somewhat tentative in this line-rich survey. From the estimate of the column density, one can derive a degree of deuteration per H atom of ~0.16, compared to ~0.036 per H atom in the case of c-C2H3DO. Such an enhancement of the degree of deuteration per H atom has also been seen for other doubly deuterated molecules compared to their mono-deuerated variants, such as CHD2CN, CHD2OCHO, CH3OCHD2, CHD2OH, and CHD2CHO.

Contributor(s): H. S. P. Müller; 08, 2012; 01, 2017; 11, 2022; 06, 2023

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