Faraday laser magnetic resonance spectroscopy of vibrationally excited C<inf>2</inf>H

Abstract

The gas phase spectrum of the C2H radical in the region between 3191 and 3342 cm-1 has been studied using a Faraday LMR spectrometer with a CO overtone laser. The C2H molecules were produced in an electric dc glow discharge of normal type containing a mixture of helium, acetylene, and hydrogen. We observed two bands of the X2Σ+ → A2∏ electronic transition with origins at 3321 and 3229 cm-1. The lower level of both bands was the first excited bending level of the electronic ground state X. The upper levels were assigned to two 2∏ vibronic levels with term values of 3693 and 3600 cm-1, respectively. They correspond to mixtures of vibrationally excited levels of the X electronic state with the lowest vibronic level of the first excited electronic 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 states. The experimentally derived values were compared with theoretical values, obtained by ab initio calculations, and could be explained by the theoretical model using an improved energy distance between the X and A states. © 1996 Academic Press, Inc.