Vibrational hot bands of linear C4 and C5 arising from a bending vibration with two quanta in the lowest bend: the (v3 + 2v5) - 2v5 band of C4 and the (v3 + 2v7) - 2v7 band of C5

Abstract

We report the complete characterization of the hot band (v3+2v₅ )-2v₅ for linear C₄ and the analogous band (v3+2v7 )-2v7 for linear C₅ via gas phase, rotationally resolved spectra. C₄ and C₅ 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: v0=1547.3164(5)cm^(-1), B=502492(18)MHz, D=0.924(52)kHz, xL=0.5802(92)cm^(-1) and q5=10.8890(26) MHz for C₄ and v0=2166.2331(3) cm^(-1), B=2576.524(87)MHz,D=0.143(13) kHz, xL=0.409(10) cm^(-1) and q7=3.9845(15) for C₅ . The results were completely consistent with linear structures and support previous conclusions with regard to the 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.