Pressure effect on the absorption and photodissociation of O2 near the dissociation threshold

The absorption and photodissociation of O-2 in the UV wavelength region, which result in 03 formation in the atmosphere, are investigated. The relevant absorption is due to Herzberg states, whose forbidden character is partly mitigated under the pressurized condition. The formation of odd oxygen species under pressurized conditions is possible even in the wavelength region longer than the dissociation threshold at 242.4 nm, and its mechanism is discussed. The latter is responsible for the initiation of the laser-induced oxidation of hydrocarbons in hydrocarbon/O-2/supercritical CO2 mixtures at 248 nm. (C) 2003 Japanese Photochemistry Association. Published by Elsevier B.V. All rights reserved.