Effects of electron scavengers in the radiolysis of water vapor

Abstract

Water vapor irradiated with X-rays in the presence of nitrous oxide gives mainly nitrogen and oxygen together with small amounts of hydrogen and, possibly, hydrogen peroxide. The yield of nitrogen, G(N2) = 3.0 ± 0.3, is constant over a wide range of conditions and G(O2) = 1.6 ± 0.3 after an induction period. The hydrogen yield is constant at low doses with G(H2) = 0.45 ± 0.1, but reaches a steady state at higher doses. The nitrogen yield is equated with the yield of scavengeable electrons in water vapor, the value g(e) = 3.0 ± 0.3 being in reasonable agreement with the theoretical value based on W(H2O) = 30 eV. Addition of other electron scavengers to water vapor containing nitrous oxide suppresses the nitrogen yield by competing efficiently for electrons. On the basis of their efficiency in suppressing the nitrogen yield, limiting values for the relative rates of reaction of N2O, SF6, CCl4, and HCl with electrons in water vapor are obtained and comparisons are made with their known electron attachment cross sections in the gas phase.