The UV–Vis spectrum of the ClCO radical in the catalytic cycle of Cl-initiated CO oxidation

Creators: Chao, Wen¹; Skog, Robert²; Frandsen, Benjamin N.^{2, 3}; Jones, Gregory H.^{1, 4}; Pham, Kayla T.⁵; Okumura, Mitchio¹; Sulbaek Andersen, Mads P.^{6, 7}; Percival, Carl J.⁸; Winiberg, Frank A. F.⁸

1. California Institute of Technology
2. University of Helsinki
3. Tampere University
4. University of Florida
5. Columbia University
6. California State University, Northridge
7. University of Copenhagen
8. Jet Propulsion Lab

Abstract

In Venus’s mesosphere, the observation/model discrepancy of molecular oxygen, O₂, abundance has been a long-standing puzzle. Chlorine atoms have been proposed as a catalyst to oxidize carbon monoxide through the formation of chloroformyl radicals (ClCO), removing O₂ and ultimately generating CO₂. However, relevant kinetic studies of this catalytic cycle are scarce and highly uncertain. In this work, we report the spectrum of the ClCO radical between 210–520 nm using a multipass UV–Vis spectrometer coupled to a pulsed-laser photolysis flow reactor at 236–294 K temperature and 50–491 Torr pressure ranges. High-level ab initio calculations were performed to simulate the observed spectrum and to investigate the electronic structure. In addition, we observed the formation of molecular chlorine, Cl₂, and phosgene, Cl₂CO, suggesting that both the terminal chlorine and the central carbon in the ClCO radical are reactive towards chlorine atoms. Most importantly, the reported spectrum will enable future measurements of essential kinetic parameters related to ClCO radicals, which are important in regulating the O₂ abundance in Venus’s mesosphere.

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Acknowledgement

The experimental research herein was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). Financial support was provided by the NASA Solar System Workings program. W.C. thanks for the fellowship support from the Josephine de Karman Fellowship Trust. R.S. thanks the Doctoral Programme in Chemistry and Molecular Sciences (CHEMS-DP) at the University of Helsinki for support. B.N.F. thanks for the fellowship support from the Carlsberg Foundation grant number CF22-0754. Computational resources for R.S. and B.N.F. were provided by the Finnish IT Center for Science (CSC). B.N.F. and R.S. acknowledge Research Council of Finland Center of Excellence VILMA grant number 346369.

Data Availability

Supporting data about error analysis, analysis of the A-band vibronic structure, details of theoretical calculations are summarized in the supplementary information. Raw data of Figures shown in this work is available on the Caltech DATA repository at https://doi.org/10.22002/s58nj-d4j78.

Supplemental Material

Transparent Peer Review file (PDF)

Supplementary Information (PDF)

Additional Information

Communications Chemistry thanks Arnaud Mahieux and the other, anonymous, reviewers for their contribution to the peer review of this work. Peer review reports are available.

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