Detection of C3 in Diffuse Interstellar Clouds

The smallest polyatomic carbon chain, C3, has been identified in interstellar clouds (Av ~ 1 mag) toward ζ Ophiuchi, 20 Aquilae, and ζ Persei by detection of the origin band in its A 1Πu-X 1Σ 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 (~1-2 × 1012 cm-2) offer a strong incentive to laboratory and astrophysical searches for the longer carbon chains. Concurrent searches for C, C, and C were negative, but provide sensitive estimates for their maximum column densities.