Detection of Interstellar Ethylene Oxide (c‐C2H4O)

Abstract

We report the identification of 10 transitions that support the detection of the small cyclic molecule ethylene oxide (c-C₂H₄O) in Sgr B2N. Although one of these transitions is severely blended, so that an accurate intensity and line width could not be determined, and two other lines are only marginally detected, we have done Gaussian fits to the remaining seven lines and have performed a rotation diagram analysis. Our results indicate a rotation temperature T_rot = 18 K and a molecular column density N(c-C₂H₄O) = 3.3 × 10¹⁴ cm^-2, corresponding to a fractional abundance relative to molecular hydrogen of order 6 × 10^-11. This is a factor of more than 200 higher than the abundance for this molecule suggested by the "new standard" chemistry model of Lee, Bettens, & Herbst. This result suggests that grain chemistry might play an effective role in the production of c-C₂H₄O. No transitions of this molecule were detected in either Sgr B2M or Sgr B2NW.