Infrared diode laser spectroscopy of C3: the ν3 band of the ã3Πu electronic state

The rotationally resolved infrared spectrum of the ν3 band of the long-lived ã3Πu electronic state of C3 has been observed between 1428 and 1473 cm−1 using a tunable diode laser spectrometer. Metastable C3 was produced in a discharge through a flowing mixture of acetylene and helium. The observed band consists of three R and three P branches, which show staggering due to Λ-type doubling and nuclear spin statistics. The band origin of 1449.5255(22) cm−1 is close to the value of 1455.3 cm−1 determined previously from matrix isolation experiments.