Abs. quantum yields for the formation of OH radicals in the laser photolysis of aq. solns. of NO3-, NO2-, and H2O2 at 308 and 351 nm and as a function of pH and temp. were detd. A scavenging technique involving the reaction between OH and SCN- ions and the time-resolved detection by visible absorption of the (SCN)2- radical ion was used to det. the abs. OH yields.