Vibrational hot bands of linear C 4 and C 5 arising from a bending vibration with two quanta in the lowest bend: the ( ν3 + 2 ν5) − 2 ν5 band of C 4 and the ( ν3 + 2 ν7) − 2 ν7 band of C 5

Abstract

We report the complete characterization of the hot band ( ν 3 + 2 ν 5) − 2 ν 5 for linear C 4 and the analogous band ( ν 3 + 2 ν 7) − 2 ν 7 for linear C 5 via gas phase, rotationally resolved spectra. C 4 and C 5 were generated using a flowing mixture of acetylene and helium subjected to a hollow cathode discharge. The spectra were recorded using a diode laser spectrometer. Σ–Σ and Δ–Δ transitions were observed for both molecular species. Analyses of these hot bands yielded the following lower state molecular parameters: ν 0 = 1547.3164(5) cm −1, B = 5024.92(18) MHz, D = 0.924(52) kHz, x L = 0.5802(92) cm −1 and q 5 = 10.8890(26) MHz for C 4 and ν 0 = 2166.2331(3) cm −1, B = 2576.524(87) MHz, D = 0.143(13) kHz, x L = 0.409(10) cm −1 and q 7 = 3.9845(15) MHz for C 5. The results were completely consistent with linear structures and support our previous conclusions with regard to semi-rigid linear nature of these two molecular species. This work represents the first conclusive study of a vibrational state with two quanta in the bend for any carbon cluster with four or more atoms.