title: The hydrocarbon ring C3H2 is ubiquitous in the Galaxy.
abstract: We report the discovery of a strong microwave (lambda 1.6 cm) spectral line, the carrier of which is common and widespread throughout the Galaxy.  A survey of a large number of sources shows that the line appears in emission in cold dust clouds, in absorption in the direction of the Galactic center, and exhibits complex profiles toward H II regions.  Toward Cas A and distant H II regions, intervening "spiral arm" clouds produce absorption. For almost all cases, the absorption features show a striking 1 : 1 radial velocity correspondence with those seen, e.g., in H2CO spectra of the same objects.  The data indicate that the line arises between low-lying energy states of  rather polar molecule.  Recent work by Thaddeus, Vrtilek, and Gottlieb, reported in 1985 incorporating the present data, shows that the line in question is the 1(10)-1(01) transition of the small hydrocarbon ring C3H2.
authors.affiliation: Herzberg Institute of Astrophysics, National Research Council of Canada.
authors.forename: H E
authors.initials: HE
authors.lastname: Matthews
authors.forename: W M
authors.initials: WM
authors.lastname: Irvine
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D019443:Cosmic Dust / Q000032:analysis*; D003521:Cyclopropanes / Q000032:analysis* / Q000737:chemistry; D005118:Extraterrestrial Environment; D006838:Hydrocarbons / Q000032:analysis; D008872:Microwaves; D013057:Spectrum Analysis
chemical_list: D019443:Cosmic Dust; D003521:Cyclopropanes; D006838:Hydrocarbons