LASER SPECTROSCOPY OF $C_{2}H$: A BAND NEAR $6340 CM^{-1}$

Author Institution: Physics Department, University of New Brunswick$C_{2}H$ is a linear radical found in a variety of terrestrial environments (flames, hydrocarbon photofragments), and is abundant in the interstellar medium. Analysis of its infrared spectrum is complicated by a low-lying electronic state $\tilde{A}^{2}\Pi$, about $3700 cm^{-1}$ above the $\tilde{X}^{2}\Sigma^{+}$ ground state. Strong interactions between $\tilde{A}^{2}\Pi$ and $\tilde{X}^{2}\Sigma^{+}$ make it difficult to assess the vibrational character of the upper states in observed spectra. In the course of near-infrared laser spectroscopic studies of a methane-helium discharge, we observed a $^{2}\Sigma - {^{2}}\Sigma$ band with an origin near $6340 cm^{-1}$. Combination difference comparisons confirmed that lower state was the $000$ vibrational level of the ground state of $C_{2}H$. The upper state may be a vibrational state of $\tilde{X}^{2}\Sigma^{+}$, or of $\tilde{A}^{2}\Pi$ if a bending vibration is involved. We will present the rotational analysis of this band, and will discuss possible vibrational assignments