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Discussion papers
https://doi.org/10.5194/acp-2018-1120
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1120
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 29 Oct 2018

Research article | 29 Oct 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

UV spectroscopic determination of the chlorine monoxide (ClO) / chlorine peroxide (ClOOCl) thermal equilibrium constant

J. Eric Klobas and David M. Wilmouth J. Eric Klobas and David M. Wilmouth
  • Harvard John A. Paulson School of Engineering and Applied Sciences and Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA

Abstract. The thermal equilibrium constant between the chlorine monoxide radical (ClO) and its dimer, chlorine peroxide (ClOOCl), was determined as a function of temperature between 228–301K in a discharge flow apparatus using broadband UV absorption spectroscopy. A third law fit of the equilibrium values determined from the experimental data provides the expression: Keq = 2.16×10−27 e(8533±25K/T)cm3molecule−1. A second law analysis of the data deviates minimally: Keq = (2.06±1.27)×10−27 e(8546±123K/T)cm3molecule−1. From the slope of the van't Hoff plot in the third law analysis, the enthalpy of formation for ClOOCl is calculated, ∆Hf (298K) = 129.9±0.6kJmol−1. The equilibrium constant results from this study suggest that the uncertainties in Keq recommended in the most recent (year 2015) NASA JPL Data Evaluation can be significantly reduced.

J. Eric Klobas and David M. Wilmouth
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J. Eric Klobas and David M. Wilmouth
J. Eric Klobas and David M. Wilmouth
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Short summary
The thermal equilibrium constant governing the partitioning of the chlorine monoxide radical (ClO) and its dimer, chlorine peroxide (ClOOCl), was measured by broadband UV spectroscopy in the temperature range of 228–301 K. Uncertainty in the value of this equilibrium constant produces significant uncertainty in model determinations of expected polar ozone loss extent. The key results of this study indicate that the currently-recommended uncertainty for this reaction may be reduced.
The thermal equilibrium constant governing the partitioning of the chlorine monoxide radical...
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