Laser-induced fluorescence spectroscopy of the A 1Πu–X 1Σ+g transition in jet-cooled C3

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 1Σ+g 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.