Detection of C$_{3}$ in Diffuse Interstellar Clouds

Abstract

The smallest polyatomic carbon chain, C$_{3}$, has been identified in interstellar clouds (A$_{v}\sim$1 mag) towards $ζ$ Ophiuchi, 20 Aquilae, and $ζ$ Persei by detection of the origin band in its $A^{1}Π_{u}-X^{1}Σ^{+}_{g}$ electronic transition, near 4052Å. Individual rotational lines were resolved up to $J$=30 enabling the rotational level column densities and temperature distributions to be determined. The inferred limits for the total column densities ($\sim$1 to 2$\times10^{12}$ 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.