Diffusion controlled reactions and exchange reactions in solution. Annual progress report

Aqueous hydrogen peroxide is reduced photochemically by dissolved hydrogen. At hydrogen peroxide concentrations above about 10-3 M, the quantum yields are quantitatively consistent with those calculated from previously published rate constants. At lower concentrations of hydrogen peroxide, observed quantum yields are lower by factors of up to 103 than are those calculated from the same rate constants. The discrepancy indicates that hydrogen atoms are being destroyed by a process having an effective first order rate constant of about 600 sec-1 and setting a maximum kinetic lifetime of about a millisecond for those atoms. This destruction may involve an impurity that is not itself destroyed by reaction with hydrogen atoms. Alternatively, it may involve a previously unobserved reaction of aqueous hydrogen atoms to form H2+ + OH-. The nature of this reaction must be established before it is clear whether or not photochemical space intermittency is a viable technique for measuring the diffusion coefficients of hydrogen atoms in water, but the existence of this reaction is of potential importance to understanding the radiation chemistry of aqueous systems. Articles published under this contract are summarized