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 Title: Near-infrared spectroscopy of ethynyl radical, C2H Author(s): Le, Anh T. Contributor(s): Sears, Trevor; Hall, Gregory Subject(s): Radicals Abstract: The ethynyl radical, \chem{C_2H}, is a reactive intermediate important in various combustion processes and also widely observed in the interstellar medium. In spite of extensive previous spectroscopic studies, the characterization of the near infrared transitions from the \textit{\~{X}}$^{2}$$\Sigma$$^{+}$ state to the mixed vibrational overtone and \textit{\~{A}}$^{2}$$\Pi states is incomplete. A strong band of \chem{C_2H} at 7064 cm^{-1} was first observed in a neon matrix and assigned as the \textit{\~{A}}^{2}$$\Pi$(002)$^{1}$ – \textit{\~{X}}$^{2}$$\Sigma$$^{+}$ transition by Forney et al.\footnote{D. Forney, M.E. Jacox, and W.E. Thompson, J. Mol. Spectrosc. 170, 178 (1995).} Subsequent theoretical work of Tarroni and Carter\footnote{R. Tarroni and S. Carter, Mol. Phys. 102, 2167 (2004).} attributed the strong absorptions in this region to transitions terminating in two upper states, each a mixture of vibrationally excited \textit{\~{X}} states and different zero-order \textit{\~{A}}-state bending levels: a $^{2}$$\Sigma$$^{+}$ symmetry combination of \textit{\~{X}}(0,2$^{0}$,3) and \textit{\~{A}}(0,3,0)$^{0}$$\kappa and a ^{2}$$\Pi$ symmetry combination of \textit{\~{X}}(0,3$^{1}$,3) and \textit{\~{A}}(0,0,2)$^{1}$. Transitions to them from the zero point level of the \textit{\~{X}} state are calculated to differ in energy by less than 10 cm$^{-1}$ and to be within a factor of two in intensity. Diode laser transient absorption was used to record Doppler-limited spectra between 7020 and 7130 cm$^{-1}$, using 193 nm photolysis of \chem{CF_3C_2H} as a source of \chem{C_2H}. Two interleaved, rotationally resolved bands were observed, consistent with a $^{2}$$\Sigma - ^{2}$$\Sigma$ transition at 7088 cm$^{-1}$ and a $^{2}$$\Pi - ^{2}$$\Sigma$ transition at 7108 cm$^{-1}$, in good accord with the Tarroni and Carter calculation. Progress on the assignment and fitting of the spectra will be reported. Acknowledgements: Work at Brookhaven National Laboratory was carried out under Contract No. DE-SC0012704 with the U.S. Department of Energy, Office of Science, and supported by its Division of Chemical Sciences, Geosciences, and Biosciences. Issue Date: 2016-06-23 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper/Presentation Type: Text Language: En URI: http://hdl.handle.net/2142/91216 Sponsor: Work at Brookhaven National Laboratory was carried out under Contract No. DE-SC0012704 with the U.S. Department of Energy, Office of Science, and supported by its Division of Chemical Sciences, Geosciences, and Biosciences. Rights Information: Copyright 2016 by the authors Date Available in IDEALS: 2016-08-22
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