LASER-INDUCED FLUORESCENCE SPECTROSCOPY OF THE (ALPHA)OVER-TILDE(1)PI(U)-(CHI)OVER-TILDE(1)SIGMA(+)(G) TRANSITION IN JET-COOLED C-3

C3 radicals have been produced in a plasma of rhenium with methane doped in helium and cooled in a supersonic free jet expansion. More than 50 vibronic bands in the laser induced fluorescence spectrum of the à 1Πu-X̃ 1Σg+ electronic transition have been recorded in the region 370-415 nm at 0.4 cm-1 resolution. The observations include bands identified by Gausset et al. (1965) and many bands not previously characterized. Rotational analyses have been made for a majority of the bands and the number of located Renner-Teller levels of the à state has been considerably extended. The (002) level is tentatively identified. A comparison of the experimentally determined energy level pattern in the à state with theoretical predictions has suggested a number of revisions to previous assignments and evidence is presented to contradict suggestions from earlier work that the (020) level of the à state is perturbed. © 1994 American Institute of Physics.