Geminate recombination dynamics studied via electron reexcitation: Kinetic analysis for anion CTTS photosystems

Recently, it became practicable to study geminate recombination dynamics of solvated electrons in polar liquids by using short pulses of light to reexcite these electrons back into the conduction band of the liquid and observe a change in the fraction of electrons that escape geminate recombination. In this Letter, the potential of this technique to provide additional insight into the recombination dynamics of electrons generated by charge-transfer-to-solvent (CTTS) photodetachment from monovalent anions in polar liquids is studied theoretically. The resulting expression accounts for the recent results from B.J. Schwartz's group at UCLA for electron photodetachment from Na- in tetrahydrofuran.Comment: 12 pages, 1 figure; to be submitted to Chem. Phys. Let

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

The picosecond geminate recombination kinetics for hydrated electrons generated by 200 nm two photon absorption (12.4 eV total energy) has been measured in both light and heavy water. The geminate kinetics are observed to be almost identical in both H2O and D2O. Kinetic analysis based upon the independent reaction time approximation indicates that the average separation between the electron and its geminate partners in D2O is 13% narrower than in H2O (2.1 nm vs. 2.4 nm). These observations suggest that, even at this high ionization energy, autoionization of water competes with direct ionization.Comment: 10 pages + 2 figures, submitted to Chem. Phys. Letter

Laser-plasma accelerator based femtosecond high-energy radiation chemistry and biology

International audienceRegarding the different protocols used for external cancer radiotherapy (X or. rays, electron, proton or ions beams) or radioimmunotherapy (Auger electron emitting radionuclides), the initial energy deposited in integrated biological systems (biomolecular and sub-cellular targets) represents a decisive parameter for the primary and more delayed radiation damage. A short-range energy distribution governs mainly (i)) the early survival probability of secondary electrons, (ii)) the spatio-temporal distribution of short-lived reactive radicals inside nascent tracks, (iii)) the primary biomolecular alterations triggered by low energy secondary electrons. The thorough understanding of these fundamental processes requires a real-time investigation of primary radiation events, typically in the temporal range 10(-14) - 10(-11) s. Laser-plasma accelerators based High Energy Radiation Femtochemistry (HERF) represents a newly emerging interdisciplinary field which can be driven in strong synergy with the generation of ultrashort particle beams in the MeV energy domain. The innovating developments of HERF would favour the investigation of prethermal radiation processes in aqueous and biochemically relevant environments. In this way, the quantum character of a very-short lived low-energy electron state (p-like configuration) represents a promising sub-nanometric probe to explore early radiation processes in native tracks. The specific properties of ultra-short electron beams accelerated by TW laser are very useful for future developments of spatio-temporal radiation biophysics in complex biological systems such as living cells

Spatio-temporal radiation biology: an emerging transdisciplinary domain. Preface

International audienc

Synergy between low and high energy radical femtochemistry

International audienceThe deleterious effects of ionizing radiation on integrated biological targets being dependent on the spatio-temporal distribution of short-lived radical processes, a thorough knowledge of these early events requires a real-time probing in the range 10(-15) - 10(-10) s. This manuscript review is focused on the synergy that exists between low (1-10 eV) and high (MeV) energy radiation femtochemistry (LERF, HERE respectively). The synergy remains crucial for the investigation of primary radical processes that take place within the prethermal regime of low energy secondary electrons. The quantum character of very-short lived electron in a prehydrated configuration provides a unique sub-nanometric probe to spatially explore some early radiation-induced biomolecular damage. This approach would foreshadow the development of innovative applications for spatio-temporal radiation biology such as, (i)) a highly-selective pro-drug activation using well-defined quantum states of short-lived radicals, (ii)) the real-time nanodosimetry in biologically relevant environments, and (iii)) the ultrashort irradiation of living cell