Large hydrated electron yields in the gamma radiolysis of acidic, oxygen-containing cysteine solutions

Abstract

The dependence of H 2 yields on cysteine concentration has been studied for aqueous, air-saturated, acidic solutions of cystein. Up to cysteine concentrations of about 5 × 10 −3 kinetic parameters and yields obtained previously for air-free, acidic solutions of cystein may be used to predict quantitatively the hydrogen yields observed. However, above these cysteine concentrations experimental yields are larger than predicted. This difference is interpreted in terms of an increase of hydrated electron yields with increasing cysteine concentration via a spur scavenging mechanism. Calculated hydrated electron yields as high as 4·5 are found are found at cysteine concentration of about 0·1 mol dm −3 and correspond with initial hydrated electron yields observed in pico-second pulse radiolysis studies of aqueous solutions. The concentration dependence of the hydrated electron yields also agrees with that predicted from these pulse radiolysis studies. An unusual effect of oxygen remains unexplained and apparently cannot be attributed to chain reactions occuring in the system.