PHOTOCHEMISTRY OF OZONE IN SOLID MIXTURES WITH ARGON

The photochemistry of solid ozone and solid solutions of ozone in argon has been investigated at 10-30 K using 266 nm laser irradiation and detection by ultraviolet and infrared absorption spectroscopies. Pure ozone is converted to O-2 with a quantum yield of 2.0+/-0.3 (independent of temperature) due to reaction of each photolytically generated O atom with a second ozone molecule. The quantum yield decreases when O-3 is diluted in argon because geminate recombination of O+O-2 becomes competitive with the O+O-3 reaction. Photodissociation of ozone monomers is thought to occur by direct cage escape, which forms a separated O+O-2 pair. This is the first experimental study in which the temperature dependence of the escape probability has been systematically investigated. The apparent activation energy of the process, 0.38+/-0.08 kJ/mol, is consistent with excitation of librations of ozone in the argon lattice, which brings it into orientations that are favorable for direct cage escape of the O atom.