Absolute line strength measurements of HO2 radical in the OO-stretching fundamental band between 1088 and 1124 cm-1 using time-resolved dual-comb spectroscopy

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

doi:10.1063/5.0244391

Absolute line strength measurements of HO2 radical in the OO-stretching fundamental band between 1088 and 1124 cm-1 using time-resolved dual-comb spectroscopy

J Chem Phys. 2025 Jan 21;162(3):034302. doi: 10.1063/5.0244391.

Authors

Che-Wei Chang^{1

2

3}, I-Yun Chen^{1

4}, Pei-Ling Luo¹

Affiliations

¹ Institute of Atomic and Molecular Sciences Academia Sinica, Taipei 106319, Taiwan.
² Molecular Science and Technology Program, Taiwan International Graduate Program, Academia Sinica, 11529 Taipei, Taiwan.
³ International Graduate Program of Molecular Science and Technology, National Taiwan University, 10617 Taipei, Taiwan.
⁴ Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan.

PMID: 39812259
DOI: 10.1063/5.0244391

Abstract

Absolute line strength measurements of hydroperoxyl (HO2) radical in the OO-stretching (ν3) fundamental band have been performed by means of mid-infrared time-resolved dual-comb spectroscopy. By employing two sets of dual-comb spectrometers, high-resolution time-resolved spectra of HO2 and HCl, formed in the photolysis reaction system of Cl2/CH3OH/O2, could be, respectively, measured near 1123 and 3059 cm-1. With kinetic simulations, spectral analysis of both HO2 and HCl, as well as the accurate line strength of the HCl R(9) transition at 3059.316 cm-1, an absolute line strength of the ν3 131,13 ← 121,12 F1,2 transitions in HO2 at 1122.983 cm-1 was first determined to be 1.80 × 10-20 cm molecule-1 with a small uncertainty down to 4% under the conditions with low initial concentrations of Cl radical (1.63-1.81 × 1013 molecule cm-3). Furthermore, broadband high-resolution spectra of the ν3 fundamental band of HO2 were recorded in the range of 1088-1124 cm-1 with an average spectral resolution of 0.002 cm-1. By contour fitting the measured broadband spectra with PGOPHER, the line strengths of hundreds of rovibrational transitions were obtained relative to the well-determined HO2 lines at 1122.983 cm-1, and those values were observed to be higher than those tabulated in the HITRAN database by a factor of ∼2.8. Moreover, the absolute band strength of the ν3 fundamental band in HO2 was derived to be 22.3 km mol-1 with an uncertainty of 5%. This work providing precise and detailed spectral data would be crucial in revisiting the theoretical modeling of HO2 geometry and updating the database of the HO2 radical.