Spectroscopy of excited states of carbon anions above the photodetachment threshold

Electronic transitions of C-3(-) and C-5(-) to states lying above the elect ron affinity of the neutral (EA) have been recorded in the gas phase by las er photodetachment spectroscopy. The excited states are identified by compa rison with absorption spectra for the mass-selected ions deposited in neon matrices and with ab initio calculations. The C (2)Sigma(u)(+)-X (2)Pi(g) t ransition and two higher energy band systems are observed for C-3(-), corre sponding to excitation energies more than 1.5 eV above the EA. In the case of C-5(-) the strongest features, at about 0.6 eV above the EA, are attribu ted to close lying (2)Delta(g)-X (2)Pi(u) and (2)Sigma(g)(-)-X (2)Pi(u) tra nsitions. The dominant configurations in these states identify them as long -lived Feshbach resonances. Lifetimes for these resonances in C-3(-) are es timated to be between 200 fs and 3 ps from the band widths.