Measurements of absolute line strength of the ν1 fundamental transitions of OH radical and rate coefficient of the reaction OH + H2O2 with mid-infrared two-color time-resolved dual-comb spectroscopy

Absolute line strengths of several transitions in the nu<INF>1</INF> fundamental band of the hydroxyl radical (OH) have been measured by simultaneous determination of hydrogen peroxide (H<INF>2</INF>O<INF>2</INF>) and OH upon laser photolysis of H<INF>2</INF>O<INF>2</INF>. Based on the well-known quantum yield for the generation of OH radicals in the 248-nm photolysis of H<INF>2</INF>O<INF>2</INF>, the line strength of the OH radicals can be accurately derived by adopting the line strength of the well-characterized transitions of H<INF>2</INF>O<INF>2</INF> and analyzing the difference absorbance time traces of H<INF>2</INF>O<INF>2</INF> and OH obtained upon laser photolysis. Employing a synchronized two-color dual-comb spectrometer, we measured high-resolution time-resolved absorption spectra of H<INF>2</INF>O<INF>2</INF> near 7.9 mu m and the OH radical near 2.9 mu m, simultaneously, under varied conditions. In addition to the studies of the line strengths of the selected H<INF>2</INF>O<INF>2</INF> and OH transitions, the kinetics of the reaction between OH and H<INF>2</INF>O<INF>2</INF> were investigated. A pressure-independent rate coefficient k<INF>OH+H<INF>2</INF>O<INF>2</INF></INF> was determined to be [1.97 (+0.10/-0.15)] x 10-12 cm3 molecule-1 s-1 at 296 K and compared with other experimental results. By carefully analyzing both high-resolution spectra and temporal absorbance profiles of H<INF>2</INF>O<INF>2</INF> and OH, the uncertainty of the obtained OH line strengths can be achieved down to <10% in this work. Moreover, the proposed two-color time-resolved dual-comb spectroscopy provides a new approach for directly determining the line strengths of transient free radicals and holds promise for investigations on their self-reaction kinetics as well as radical-radical reactions.