Hot band analysis and kinetics measurements for ethynyl radical, C2H, in the 1.49 μm region

Le, Anh T.

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https://hdl.handle.net/2142/96915 Copy

Description

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

Issue Date

2017-06-20

Keyword(s)

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.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/96915

DOI

https://doi.org/10.15278/isms.2017.TB05

Copyright and License Information

Copyright 2017 Anh T. Le

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