High energy radiation femtochemistry of water molecules: early electron-radical pairs processes

Y. A. Gauduel; Y. Glinec; J.-P. Rousseau; F. Burgy; V. Malka

doi:10.1140/epjd/e2010-00152-2

2024 Impact factor 1.5

Atomic, Molecular, Optical and Plasma Physics

Eur. Phys. J. D 60, 121-135 (2010)
https://doi.org/10.1140/epjd/e2010-00152-2

High energy radiation femtochemistry of water molecules: early electron-radical pairs processes

Y. A. Gauduel^a, Y. Glinec, J.-P. Rousseau, F. Burgy and V. Malka

Laboratoire d'Optique Appliquée, CNRS UMR 7639, École Polytechnique ParisTech – ENSTA ParisTech, 91761 Palaiseau Cedex, France

Corresponding author: ^a yann.gauduel@ensta.fr

Received: 17 December 2009
Revised: 12 April 2010
Published online: 11 June 2010

Abstract

The damages triggered by ionizing radiation on chemical and biological targets depend on the survival probability of radicals produced in clusters of ionization-excitation events. In this paper, we report on femtolysis (FEMTOsecond radioLYSIS) of pure liquid water using an innovative laser produced high-energy, ultra-short electron bunches in the 2.5-15 MeV range and high energy radiation femtochemistry (HERF) measurements. The short-time monitoring of a primary reducing radical, hydrated electron e $^{-}_{aq}$ , has been performed in confined ionization spaces (nascent spurs). The calculated yield of hydrated electrons at early time, $G({\rm e}^{-}_{aq})_{ET}$ , is estimated to be 6.5 ± 0.5 (number/100 eV) at t ~ 5 ps after the ultrafast energy deposition. This estimated value is high compare to (i) the available data of previous works that used scavenging techniques; (ii) the predictions of stochastic water radiolysis modelling for which the initial behaviour of hydrated electron is investigated in the framework of a classical diffusion regime of independent pairs. The HERF developments give new insights into the early ubiquitous radical escape probability in nascent aqueous spurs and emphasize the importance of short-lived solvent bridged electron-radical complexes [ ${\rm H}_{3}{\rm O}^{+...}$ ${\rm e}_{aq}^{-}$ .. ${\rm OH}]_{n{\rm H}_2{\rm O}}$ (non-independent pairs). A complete understanding of the G( ${\rm e}^{-}_{aq})_{ET}$ value needs to account for quantum aspects of 1s-like trapped electron ground state and neoformed prototropic radicals that govern ultra-fast recombination processes within these non-independent pair configurations. Femtolysis data emphasize that within a time-dependent non-diffusion regime, spatio-temporal correlations between hydrated electron and nearest neighbours OH radical or hydrated proton ( ${\rm H}_{3}{\rm O}^{+}$ ) would assist ultrafast anisotropic 1D recombination within solvent bridged electron-radical complexes. The emerging HERF domain would provide guidance for understanding of ultrashort-lived sub-structure of tracks and stimulate future semi-quantum simulations on prethermal radical reactions.