Analysis of the A - X bands of the ethynyl radical near 1.48 μm and re-evaluation of (X)over-tildestate energies

We report the observation and analysis of spectra in part of the near-infrared spectrum of C2H, originating in rotational levels in the ground and lowest two excited bending vibrational levels of the ground (X) over tilde (2)Sigma(+) state. In the analysis, we have combined present and previously reported high resolution spectroscopic data for the lower levels involved in the transitions to determine significantly improved molecular constants to describe the fine and hyperfine split rotational levels of the radical in the zero point, v(2) = 1 and the (2)Sigma(+) component of v(2) = 2. Two of the upper state vibronic levels involved had not been observed previously. The data and analysis indicate the electronic wavefunction character changes with bending vibrational excitation in the ground state and provide avenues for future measurements of reactivity of the radical as a function of vibrational excitation. (C) 2018 Elsevier Inc. All rights reserved.