Gas phase electronic spectrum of T-shaped AlC2 radical.

Gas phase electronic transitions for the C 2B2<--X 2A1 and D 2B1<--X 2A1 band systems of T-shaped AlC2 (C2v) radical have been measured in the 345-475 nm range. Vibrational analyses of both band systems are reported. Simulation of several rotationally resolved bands confirms previously obtained rotational parameters for the C 2B2 state. The radical is produced by ablating an aluminum rod in the presence of acetylene gas. The resulting supersonic molecular beam is probed using both mass-selective resonant two-color two-photon ionization and laser induced fluorescence. Ab initio calculations and vertical electronic excitation energies help the assignment. Vibrational frequencies for the X 2A1, C 2B2, and D 2B1 states have been determined. Rotational analysis of a number of bands yields spectroscopic constants for one vibronic state in the C 2B2 manifold and the origin band of the D 2B1<--X 2A1 system.