Oxirane in the ISM

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-C2H4O)
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.

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