Vibronic bands of the CCH radical observed by infrared diode laser kinetic spectroscopy

Abstract

Five infrared bands of the CCH radical were observed by diode laser kinetic spectroscopy. Two Π–Π type bands were assigned to hot bands from the (0110) state in X̃ 2Σ+, namely to ν2+ν3−ν2 and 7ν12−ν12. The latter band was found to share the upper state with a Π–Σ type band, of which the lower state was the ground vibronic state. Two other Π–Σ type bands corresponded to transitions from the ν3 state in X̃ 2Σ+ to two vibronic Π states. Simultaneous analysis of all the observed bands yielded molecular parameters with high precision including the ν2 fundamental frequency, which was determined to be 371.6034 (3) cm−1. The parity of each rovibronic level was determined unambiguously because Π–Σ+ transitions were observed, allowing us to choose the signs of K-type doubling constants p and q uniquely.