Solvated Electron Extinction Coefficient and Oscillator Strength in High Temperature Water

Abstract

The decadic extinction coefficient of the hydrated electron is reported for the absorption maximum from room temperature to 380 degrees C. The extinction coefficient is established by relating the transient absorption of the hydrated electrons in the presence of a scavenger to the concentration of stable product produced in the same experiment. Scavengers used in this report are SF(6,) N(2)O, and methyl viologen. The room temperature value is established as 22,500 M(-1) cm(-1), higher by 10-20% than values used over the last several decades. We demonstrate how previous workers arrived at a low value by incorrect choice of a radiolysis yield value. With this revision, the integrated oscillator strength, corrected by refractive index, is definitely (ca. 10%) larger than unity. This result is fully consistent with EPR and resonance Raman results which indicate mixing of the hydrated electron wave function with solvent electronic orbitals. Oscillator strength appears to be conserved vs temperature.

Theoretical Studies of Spectroscopy and Dynamics of Hydrated Electrons

“…This approximation neglects electron correlation and also assumes that the physical attributes of the hydrated electron system arise from elementary events of single electron character. Although this is not strictly so, as has been demonstrated experimentally, 26,42 these effects appear to be minor. Within the one-electron picture, the electron-water molecule pseudopotential and the classical water force field limit the accuracy of the theoretical treatment.…”

A one-electron model for the aqueous electron that includes many-body electron-water polarization: Bulk equilibrium structure, vertical electron binding energy, and optical absorption spectrum

“…Unlike our previous model ͑PEWP-1͒, 79 which afforded promising results for ͑H 2 O͒ n − clusters but failed to localize the electron in the condensed phase, the new parametrization performs at least as well for clusters ͑as judged by comparison to ab initio benchmarks͒, but also qualitatively reproduces various experimental data for e aq − in bulk water. As Shkrob et al 61,62 and others 29,59 have argued, quantitative reproduction of structural features and experimental parameters may require many-electron quantum mechanics. Nevertheless, the PEWP-2 model affords a VEBE and an optical absorption spectrum that are in far better agreement with experiment than are previous one-electron models, while structural and dynamical features, such as the radius of gyration and diffusion coefficient, are at least qualitatively correct.…”

The Hydrated Electron

“…In these calculations, the polarization response of the water molecules plays a crucial role in amplifying the oscillator strengths of the states in question. This is interesting in view of a measured value of 1.14 for the integrated oscillator strength of the e − (aq ) absorption spectrum (131). A value >1 implies that excitation of e − (aq ) is not strictly a one-electron transition but rather some intensity is borrowed from electrons on water molecules.…”