Isotopic dependence of recombination kinetics in water

Abstract

The decay of the hydrated electron solvated by D/sub 2/O molecules, e/sub aq//sup /minus// (D/sub 2/O), and the OD radical as well as the reactions of the precursor of the hydrated electron have been investigated in D/sub 2/O solution by using the Argonne stroboscopic pulse radiolysis system. These processes have been compared to the analogous reactions in H/sub 2/O. The decay of the electron is slower in D/sub 2/O relative to the corresponding species in H/sub 2/O, while the decay of the hydroxyl radical and the efficiencies of the electron scavengers in reducing the initial yield of the hydrated electron are comparable in both solvents. The OD radical absorbance decays to 0.75 /plus minus/ 0.06 of its initial value from 200 ps to 3.0 ns. This parallels that for the OH radical (0.74 /plus minus/ 0.06). The similarity of the electron scavenging efficiencies indicate a hydrated electron precursor that exists in a distinct, localized state for both D/sub 2/O and H/sub 2/O. The slower decay of the electron in D/sub 2/O has been interpreted as a greater thermalization distance and a broader initial spatial distribution for the electron in D/sub 2/O compared to H/sub 2/O. The spurs of the D/submore » 2/O and H/sub 2/O systems have been modeled by using a spherically symmetric electron distribution around a Gaussian hydroxyl radical core. The computer simulations agree quite favorably with the experimental results.« less