The γ-radiolysis of water vapour in the presence of NH3 and O2

Abstract

Measurements of H₂ production from pure water vapour as a function of dose indicate that, like liquid water, it is essentially stable to γ radiation. The net yield of H₂ is very low leading to a mean integral value of G(H₂)∼0.007 but the amount of H₂ obtained depends critically on the care taken in cleaning the cells and admitting the water, and it is concluded that previously-published yields are all integral values obtained under a variety of conditions. Measurement of the primary yields in the presence of NH₃ and of NH₃+O₂ gives g(OH)= 6.6±0.2, g(H)= 5.7±0.2, g(H₂)= 0.47±0.01, but no distinction can be made between yields of electrons and H atoms in this work. Primary processes of ionization and charge recombination are considered in view of earlier postulates, together with physical evidence which demonstrates the stability of ion clusters in water vapour even at low pressures. It is suggested that, under certain conditions in the vapour phase, charge neutralization of the H₃O⁺ ion leads to the same yield of radicals as in liquid water.