Effect of Gamma Radiation on Silica Gel, (II)

Radiolysis of N₂O adsorbed on silica gel degassed at 200, 450 and 600°C has been studied to investigate the behavior of electrons on the gel surface. The G-value of nitrogen as the major radiolytic product increases with an increase of N₂O concentration adsorbed approaching a plateau value which depends on degassing temperature of the gel prior to irradiation. By the competitive electron scavenging of N₂O with several electron scavengers, such as CCl₄, SF₆ and nitrobenzene, initial yield of electrons G (e ^?), and relative rate constant for reaction of electrons with scavenger to that with N₂O, k _s /k _N2O, have been obtained. The G (e ^?) is 3.8 and 2.0 for the gel degassed at 200 and 600°C respectively. In the former gel, the value of k _s /k _N2O is comparable with that in aqueous system, while in the latter, with that in non-polar hydrocarbon such as neopentane. The observed difference may be attributed to the presence of silanol groups and residual water which facilitate some form of hydration of electrons on the gel degassed at low temperature. Despite of the complexity of the heterogeneous system, Hammett's relationship is observed among the reactions of electrons with monosubstituted derivatives of benzene, providing the reaction constant ρ as 2.8.