Hydroxyl radical consumption following photolysis of vapor-phase hydrogen peroxide at 266 nm: Implications for photofragmentation laser-induced fluorescence measurements of hydrogen peroxide

Abstract

The decay of OH concentration following photolysis of room-temperature vapor-phase hydrogen peroxide is studied as a function of photolysis fluence at 266 nm in an open air environment. The rate of decay is found to increase with increasing photolysis fluence, i.e., with increasing number of photodissociated H2O2(g) molecules. Single-exponential functions approximate the OH concentration decay rather well, even for higher photolysis levels, and the decay time is shown to be inversely proportional to the H2O2(g) concentration. For fluences of about 450 mJ/cm2 the difference between a single-exponential decay and measured data is becoming evident after approximately 150 μs. Calculations based on a chemical kinetics model agree well with experimental data also for times >150 μs. By combining the model with measurements, the actual photolysis levels used in experiments are estimated. The best fit between measured data and the model suggests that about 1.1% of the H2O2(g) molecules are dissociated with a photolysis fluence of ∼450 mJ/cm2, in reasonable agreement with a Beer–Lambert based estimation. Excitation scans did not unfold any differences between OH spectra recorded at different photolysis fluences.