2001ApJ...553..267M

The smallest polyatomic carbon chain, C₃, has been identified in interstellar clouds (A_v∼1 mag) toward ζ Ophiuchi, 20 Aquilae, and ζ Persei by detection of the origin band in its A¹Π_u-X¹Σ⁺_g electronic transition, near 4052 Å. Individual rotational lines were resolved up to J=30, allowing the rotational-level column densities and temperature distributions to be determined. The inferred limits for the total column densities (∼1-2x10¹² cm^–2) offer a strong incentive to laboratory and astrophysical searches for the longer carbon chains. Concurrent searches for C⁺₂, C^–₂, and C^–₃ were negative, but provide sensitive estimates for their maximum column densities.