Geminate recombination of hydroxyl radicals generated in 200 nm photodissociation of aqueous hydrogen peroxide

Abstract

The picosecond dynamics of hydroxyl radicals generated in 200 nm photoinduced dissociation of aqueous hydrogen peroxide have been observed through their transient absorbance at 266 nm. It is shown that these kinetics are nearly exponential, with a decay time of ca. 30 ps. The prompt quantum yield for the decomposition of H 2 O 2 is 0.56, and the fraction of hydroxyl radicals escaping from the solvent cage to the water bulk is 64-68%. These recombination kinetics suggest strong caging of the geminate hydroxyl radicals by water. Phenomenologically, these kinetics may be rationalized in terms of the diffusion of hydroxide radicals out of a shallow potential well (a solvent cage) with an Onsager radius of 0.24 nm.

Ultrafast dynamics for electron photodetachment from aqueous hydroxide

“…[40] A diode-pumped 5 W Nd:YVO laser was used to pump a Kerr lens mode-locked Ti:sapphire laser operating at 80 MHz (Spectra Physics Tsunami). The 45 fs pulses from the oscillator where stretched to 80 ps in a single grating stretcher.…”

Electron Photodetachment from Aqueous Anions. 1. Quantum Yields for Generation of Hydrated Electron by 193 and 248 nm Laser Photoexcitation of Miscellaneous Inorganic Anions

“…1(a) is accounted for by the absorption of 248 nm light by hydroxyl radicals generated by the laser pulse (as shown elsewhere, these radicals escape from the solvent cage in ca. 30 ps [42]). Czapski and…”

“…2S(a)). As explained elsewhere [42], side reactions of hydroxyl radicals (e.g., with peroxide itself [43]) and cross recombination were too slow to compete with rxn. (19) (carbonate radical was formed in 200 ns); the decay of the carbonate radicals was also too slow (5-15 µs) to deplete the concentration of these radicals at t=200 ns ( Fig.…”

Geminate recombination of electrons generated by above-the-gap (12.4 eV) photoionization of liquid water

“…[16] The picosecond transient absorption (TA) measurements were carried out using a 1 kHz Ti:sapphire setup, details of which are given in refs. [16,17,18]. This setup before and after the sample, was monitored using a thermopile power meter.…”

“…[16,17,18 Using the "independent reaction time" (IRT) model developed by Pimblott, [24] which is commonly used to simulate the geminate dynamics of water spurs, the decay water is narrower than in the light water. While the quality of these kinetic traces does not allow us to put accurate confidence limits on these estimates, it is clear from Fig.…”