Laser---Induced Fluorescence of the $C_{2}H$ Radical

Abstract

Four $^{2}\Pi^{-2}\Pi$ vibronic bands and one $^{2}\Phi-^{2}\Phi$ band of $C_{2}H$ have been analyzed in the spectral interval $34500-40000 cm^{-1}$. These bands have been detected by laser-induced fluorescence following the 193 nm photolysis of acetylene. The rotational constants, $B^{11}$ of these bands are in the interval of 1.4397-1.$4534 cm^{-1}$ and the B values are in the range of $1.2132-1.2435 cm^{-1}$. Small spin-orbital constants of the $^{2}\Pi-^{2}\Pi$ transitions were obtained, indicating that the corresponding lower states of these transitions have more than 90\% of the \~X--state character. Based upon the observed dispersed fluorescence spectra from some of the $^{2}\Pi-^{2}\Pi$ transitions, we assign the lower states of these transitions to the high-vibrational levels of the \~X states. The pertinent upper states of these transitions are most likely due to $2^{2}\Pi$ electronic state.