Detection of C3 in diffuse interstellar clouds

The smallest polyatomic carbon chain, C-3, has been identified in interstellar clouds (A(upsilon)similar to 1 mag) toward zeta Ophiuchi, 20 Aquilae and zeta Persei by detection of the origin band in its A(1)II(u)-X(1)Sigma (+)(g) electronic transition, near 4052 Angstrom. 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 (similar to1-2 x 10(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.