DIFFUSION-LIMITED GEMINATE RECOMBINATION OF O-2 IN SOLID XENON(O)

The thermally activated recombination reaction O+O-2-->O-3 is observed in solid xenon matrices and in free-standing crystals of xenon at 14- 25 K on the time scale 10(2)-10(5) s. The reactants are prepared as sp atially separated O...O-2 pairs immobilized in solid Xe at 10 K by 266 nm photodissociation of O-3 precursor molecules. The temperature depe ndence of the ozone recovery rate yields an activation energy for diff usion of O atoms in solid xenon of 2.0+/-0.5 kJ/mol. This value also r epresents an upper limit to the potential energy barrier to the O+O-2 recombination reaction itself. In dilute samples (mole fraction of ozo ne less than 2X10(-4)) more than 90% of the initial O-3 is recovered d uring the warming cycle. Only a small fraction of O atoms (<20%) escap e geminate recombination with the partner oxygen molecule within the p air and react with other O, molecules or O atoms. The experimental res ults are interpreted within the framework of a continuous diffusion mo del in which the initial spatial distribution of reactants is nonrando m. (C) 1996 American Institute of Physics.