RECENT RESULTS FROM PULSE RADIOLYSIS
Authors: SWALLOW A. J. 
Published: January 2008

Abstract— The technique of pulse radiolysis has come into widespread use only within the last few years. It is the high‐energy analogue of flash photolysis, and is providing a new insight into the chemistry of excited states, ions, and free radicals. In the method most commonly used, a pulse of high‐energy radiation (about 1‐1,000 nsec) is applied to the system under investigation (usually a liquid). A steady beam of light passing through the system enables changes in absorbance to be observed over periods from about 1 to 10 nsec after the pulse. Alternatively, any emission resulting from the pulse can be seen. Much of the work has been with aqueous solutions. The hydrated electron has been shown to react only very slowly with water, but it reacts with many solutes with second‐order rate constants of up to about 2 × 1010M‐1 sec‐1. The reactions of products formed can be observed. For example, when hydrated electrons react with carbon monoxide they appear to give rise to hydrated formyl radicals, which react with each other with 2k= 5 × 108M‐1 sec‐1. In the field of substances of biological interest, the formation and reactions of free radicals from riboflavin and nicotinamide adenine dinucleotide have been studied. The rates of numerous other reactions of free radicals, including peroxy radicals, have been measured in aqueous solution. When aliphatic hydrocarbons are irradiated, most of the electrons produced return to the positive ions, but when solutes such as anthracene or naphthalene are present at high enough concentration the electrons can be captured by the solute. Neutralization then occurs rapidly giving rise to excited solute molecules. With styrene as solute, anion formation can be seen and the recombination observed. Other reactions of styrene intermediates have also been observed quantitatively, in the pure state as well as in various solutes. In the irradiation of solutions of iodine in cyclohexane various free‐radical reactions have been observed, the charge‐transfer complex of iodine atoms with the solvent being an important intermediate. Similar complexes have been observed in the irradiation of pure alkyl iodides.RESUMENLa técnica de radiólisis de pulso ha comenzado a usarse ampliamente en los últimos ańos. El método más usado consiste en un pulso de radiación de alta energia, alrededor de 1‐1·000 nsec, aplicado al sistema en investigatión (generalmente un líquido). Un rayo de Iuz constante pasando a través del sistema permite observar cambios en la absorción en periodos de 1 a 10 nsec después del pulso. Alternativamente puede observarse cualquier emisión que resulte del pulso. Se ha demostrado que el electrón hidratado reacciona muy lentamente con agua, pero lo hace con muchos solutos con constantes de velocidad de segundo orden de hasta 2 × 1010M‐1 sec‐1. Cuando los electrones hidratados reaccionan con monóxido de carbono se forman radicales formilo hidratados que reaccionan entre ellos con una 2k= 5 × 108M sec‐1. Se han estudiado la formación de radicales libres y reacciones de riboflavina y nicotinamida adenina dinucleótido. Cuando se irradian hidrocarburos alifáticos, la mayor parte de los electrones producidos retornan a los iones positivos, pero cuando solutos tales como el antraceno o naftaleno estan presentes a alta concentratión pueden capturar los electrones. La neutralizatión ocurre rapidamente aumentando las moléculas de soluto excitadas. Cuando el soluto es estireno puede observarse la formación del anión y la recombinatión del mismo. Se han observado varias reacciones de radicales libres en soluciones irradiadas de iodo en ciclohexano, los complejos “charge‐transfer” de los átomos de iodo con el solvente son intermediaries importantes. Complejos similares se han observado cuando se irradian yoduros de alquilo.