Cavity ring-down UV spectroscopy of the C2Σ+-X2Π electronic transition of CH

Abstract

Abstract Rotationally resolved spectra of the C2Σ+-X2Π electronic system of the CH radical were measured using cavity ring-down spectroscopy in supersonically expanding, planar hydrocarbon plasma. The experimental conditions allowed the study of highly excited rotational levels starting from vibrationally excited states. Here we present some 200+ new or more accurately recorded transitions in the 0–0, 1–1 and 2–2 vibronic bands in the ultraviolet between 30900 and 32400\u202fcm−1 (324–309\u202fnm). The resulting data, compared to earlier measurements, allows for the determination of more precise molecular constants for each vibrational state and therefore more precise equilibrium values. From this an equilibrium bond length of 1.115798(17)\xa0A for the C2Σ+ state is determined. A comprehensive list with observed transitions for each band has been compiled from all available experimental studies and constraints are placed on the predissociation lifetimes.