Irradiation of gaseous NO2 with the 488 nm line of an argon ion laser during its reaction with C2H4 over a Pt catalyst at 250 C resulted in up to a fourfold increase in the CO2 product yield. This enhancement is believed to result from the reaction of vibrationally excited NO2 with adsorbed C2H4 or a species derived from it. The observed effect disappeared after a period of time due to surface poisoning. Hydroxyl radicals have been detected leaving the surface of Pt and Rh-Pt catalysts during the reaction of H2 and 02 at 600-800 C. The OH radical was detected by its fluorescence at 340 nm induced by a dye laser, both in the gas phase and in an Ar matrix at 10 K. The activation energies for OH production from Pt and Rh-Pt surfaces have been determined.