John P. Maier

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 A. 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.

Bound electronic states X1Σ+, a3Π and A1Π of C2B-

Large-scale electronic structure calculations were performed to generate a three-dimensional potential energy function for the X1Σ+ state of C2B-. Spectroscopic constants and anharmonic ro-vibrational levels were calculated variationally and by perturbation theory using this function. The ground state possesses an equilibrium geometry with ReCC=1.270 Aand ReCB=1.461 A, the fundamental vibrational transitions are predicted at ν1CB(J=0)=1014.7 cm-1, ν2(J=1)=125.4 cm-1 and ν3CC(J=0)=1935.4 cm-1 (exp. 1936.3 cm-1). The difference electron density plot showed that the negative charge is almost entirely localized in the boron lone pair and the BC bond region. The A1Π–XΣ+Te excitation energy was calculated to be 23722 cm-1 confirming the assignment made for the transition detected at T0=23131 cm-1 in a neon matrix. For the A1Π state an equilibrium geometry with ReCC=1.324 Aand ReCB=1.396 Awas obtained. The vertical excitation energy of the a3Π–X 1Σ+ transition is predicted at 15306 cm-1. Both excited states lie below the vertical detachment energy calculated at 25845 cm-1.