FARADAY LASER MAGNETIC-RESONANCE SPECTROSCOPY OF VIBRATIONALLY EXCITED C2H

The gas phase spectrum of the C2H radical in the region between 3191 a nd 3342 cm(-1) has been studied using a Faraday LMR spectrometer with a CO overtone laser. The C2H molecules were produced in an electric de glow discharge of normal type containing a mixture of helium, acetyle ne, and hydrogen. We observed two bands of the X(2) Sigma(+) --> A(2) Pi electronic transition with origins at 3321 and 3229 cm(-1). The low er level of both bands was the first excited bending level of the elec tronic ground state X. The upper levels were assigned to two (2) Pi vi bronic levels with term values of 3693 and 3600 cm(-1), respectively. They correspond to mixtures of vibrationally excited levels of the X e lectronic state with the lowest vibronic level of the first excited el ectronic state A. From the analysis of the spectra we could determine the orbital g factors of the upper levels. These parameters are a very sensitive measure for the mixing between the X and A electronic state s. The experimentally derived values were compared with theoretical va lues, obtained by ab initio calculations, and could be explained by th e theoretical model using an improved energy distance between the X an d A states. (C) 1996 Academic Press, Inc.