Primary trapping and solvated electron yields. Part 1. Recombination kinetics. Part 2. Correlation between G-value and neutralization efficiency

Abstract

The isothermal decay of luminescence emitted in frozen hydrocarbons as a result of the recombination of trapped electrons with aromatic solute cations has been studied in relation to theoretical models for the primary processes of radiolysis. The kinetics were determined on a time scale extending from -20 to 800 ns, with radiations of different LET.In polar liquids the influence of physical as well as chemical properties of the solvent on the yield G(e,,,) at a given time ( t = 3 ns) has been investigated: in particular, evidence was found of the existence of a correlation between the survival probability of eGlv and the efficiency factor of the eS;,,-cation recombination, which had so far been assumed to be limited only by diffusion.* bPBD = 2-(4-butylphenyl) 5-(4-biphenylyl)l,3,4-oxadiazole. PTP = p-terphenyl.

Picosecond Pulse Radiolysis of Propylene Carbonate as a Solute in Water and as a Solvent

“…The mechanism of water radiolysis is the best known . Comparison with other solvents is the way to establish a general description …”

“…1 Comparison with other solvents is the way to establish a general description. 2 The radiolysis also enables the observation of electrons solvated in various liquids and the comparison of their optical and reactivity properties (alcohols, amines, ethers, alcanes). 3,4 Recent radiolysis studies have been devoted to the group of ionic liquids.…”

Femtosecond Two-Photon Ionization and Solvated Electron Geminate Recombination in Liquid-to-Supercritical Ammonia

“…This interpretation was further corroborated by a stopped-flow measurement of the kinetics of the reaction using solvated electrons from a metal ammonia solution on the one hand and ammonium cations from a solution of NH 4 Br in liquid ammonia on the other . At 223 K, the measured second-order rate constant for reaction is 1.2 × 10 6 M –1 s –1 , which is several orders of magnitude smaller than the calculated diffusion limit of 5.0 × 10 11 M –1 s –1 . , A lower limit for the reaction barrier can be estimated from thermochemical data published by Schindewolf according to whom the reaction enthalpy for reaction is +30 kJ/mol, while the reaction entropy is −12 J/mol K. Thus, the charge neutralization is not only endothermic but in the temperature range studied here, also endergonic by at least 33 kJ/mol! Therefore, the charge neutralization reaction can safely be neglected …”

“…This fraction represents a solvated electron population that appears quasi-stationary on the subnanosecond time scale of the experiment and becomes apparent as an asymptotic pump-induced absorption for long pump–probe delays. Nongeminate recombination of solvated electrons in liquid ammonia is temporally very well separated from the geminate recombination and occurs in a homogeneous second-order reaction on time scales well in excess of 1 ns extending even into the microsecond regime. − …”

“…Reaction was found to be diffusion-controlled. , In other words, the reaction of the solvated electron with NH 2 radicals under formation of the amide anion features no significant energy barrier, and consequently, every encounter between the two particles is reactive. In this case, the temperature and density dependence of the reaction rate is governed by the diffusion coefficients of the recombining particles.…”