Accurate Kinetic Studies of OH + HO2 Radical-Radical Reaction through Direct Measurement of Precursor and Radical Concentrations with High-Resolution Time-Resolved Dual-Comb Spectroscopy

I-Yun Chen; Che-Wei Chang; Christa Fittschen; Pei-Ling Luo

doi:10.1021/acs.jpclett.4c00494

Accurate Kinetic Studies of OH + HO₂ Radical-Radical Reaction through Direct Measurement of Precursor and Radical Concentrations with High-Resolution Time-Resolved Dual-Comb Spectroscopy

J Phys Chem Lett. 2024 Apr 11;15(14):3733-3739. doi: 10.1021/acs.jpclett.4c00494. Epub 2024 Mar 28.

Authors

I-Yun Chen^{1

2}, Che-Wei Chang^{1

3

4}, Christa Fittschen⁵, Pei-Ling Luo¹

Affiliations

¹ Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106319, Taiwan.
² Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan.
³ Molecular Science and Technology Program, Taiwan International Graduate Program, Academia Sinica, 11529 Taipei, Taiwan.
⁴ International Graduate Program of Molecular Science and Technology, National Taiwan University, 10617 Taipei, Taiwan.
⁵ University Lille, CNRS, UMR 8522, PC2A-Physicochimie des Processus de Combustion et de l'Atmosphère, F-59000 Lille, France.

Abstract

The radical-radical reaction between OH and HO₂ has been considered for a long time as an important reaction in tropospheric photochemistry and combustion chemistry. However, a significant discrepancy of an order of magnitude for rate coefficients of this reaction is found between two recent experiments. Herein, we investigate the reaction OH + HO₂ via direct spectral quantification of both the precursor (H₂O₂) and free radicals (OH and HO₂) upon the 248 nm photolysis of H₂O₂ using infrared two-color time-resolved dual-comb spectroscopy. With quantitative and kinetic analysis of concentration profiles of both OH and HO₂ at varied conditions, the rate coefficient k_OH+HO₂ is determined to be (1.10 ± 0.12) × 10^-10 cm³ molecule^-1 s^-1 at 296 K. Moreover, we explore the kinetics of this reaction under conditions in the presence of water, but no enhancement in the k_OH+HO₂ can be observed. This work as an independent experiment plays a crucial role in revisiting this prototypical radical-radical reaction.