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

• Published in: The journal of physical chemistry letters Vol. 15; no. 14; pp. 3733 - 3739
• Main Authors: Chen, I-Yun, Chang, Che-Wei, Fittschen, Christa, Luo, Pei-Ling
• Format: Journal Article
• Language: English
• Published: American Chemical Society 11.04.2024
• Subjects: Letter; Physical Insights into Chemistry, Catalysis, and Interfaces
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.4c00494

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.