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 Title: HOT BAND ANALYSIS AND KINETICS MEASUREMENTS FOR ETHYNYL RADICAL, C2H, IN THE 1.49 μm REGION Author(s): Le, Anh T. Contributor(s): Sears, Trevor; Hall, Gregory Subject(s): Mini-symposium: Multiple Potential Energy Surfaces Abstract: Ethynyl, C$_2$H, is an important intermediate in combustion processes and has been widely observed in interstellar space. Spectroscopically, it is of particular interest because it possesses three low-lying electronic surfaces: a ground $^2Sigma^+$state, and a low-lying $^2Pi$ excited electronic state, which splits due to the Renner-Teller effect. Vibronic coupling among these states leads to a complicated, mixed-character, energy level structure. We have previously reported workfootnote{scriptsize{A. T. Le, G. E. Hall, T. J. Sears, textit{J. Chem. Phys.} textbf{145} 074306, 2016 }} on three bands originating from the $tilde{X}(0,0,0),^2Sigma$ ground state to excited vibronic states: two $^2Sigma, -, ^2 Sigma$ transitions at 6696 and 7088 wn and a $^2Pi, -, ^2Sigma$ transition at 7108 wn. In this work, the radicals were formed in a hot, non-thermal, population distribution by textit{u.v.} pulsed laser photolysis of a precursor. Kinetic measurements of the time-evolution of the ground state populations following collisional relaxation and reactive loss were also made, using some of the stronger rotational lines observed. Time-dependent signals in mixtures containing a variable concentration of precursor in argon suggested that vibronically hot C$_2$H radicals were less reactive than the relaxed, thermalized, radical. Two additional hot bands originating in states $tilde{X}(0,1^1,0),^2Pi$ and $tilde{X}(0,2^0,0),^2Sigma$, have now been identified in the same spectral region. In a new series of experiments, we have measured the kinetics of formation and decay of representative levels involving all the assigned transitions, i.e. originating in $tilde{X}(0,v_2,0)$, with $v_2 =0 ,1, mathrm{and}, 2$, in various concentrations of mixtures of precursor, inert gas and hydrogen. The new spectra also show greatly improved signal-to-noise ratio in comparison to our previous work, due to the use of a transient FM detection scheme, and additional spectral assignments seem likely. Both kinetics and spectroscopic results will be described in the talk. _x000d_ _x000d_ textbf{Acknowledgments}: 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 within the Office of Basic Energy Sciences. Issue Date: 6/20/2017 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/96915 DOI: 10.15278/isms.2017.TB05 Date Available in IDEALS: 2017-07-27
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