H atom yields in the radiolysis of water

Experimental measurements of molecular hydrogen including the use of isotopic techniques are combined with track model calculations to determine H atom yields in the radiolysis of water. The production of H atoms in the radiolysis of water is relatively small, but is important for fundamental considerations. H atoms are formed by the decay of excited states of water at the sub-picosecond timescale and by hydrated electron reactions during the diffusion-kinetic evolution of the ion track up to microseconds. The competition between H atom loss by combination reactions and its formation by reactions of the hydrated electron makes prediction of the H atom kinetics very difficult. H atom yields determined by subtraction of total molecular hydrogen production in neat water from that observed in the formate solutions is found to agree well with the more direct measurement of HD using deuterated formate as a scavenger. H atom yields are found to decrease with the evolution of the radiation track and decrease with increasing LET. Monte Carlo track model calculations are used to analyze the measured experimental yields and to elucidate the underlying H atom kinetics in the radiolysis of water.