Suppression of inhibition of substrate photodegradation by scavengers of hydroxyl radicals: the solvent-cage effect of bromide on nitrate photolysis

In this paper we show that bromide scavenges the · OH radicals formed upon photolysis of nitrate, before they leave the solvent cage. Bromide can thus inhibit the in-cage recombination between · OH and · NO 2 . The consequence is an increased generation of · NO 2 and nitrite and of Br 2 −· + · OH, compared to · OH alone in the absence of bromide. We show that this effect compensates for the lower reactivity of Br 2 −· compared to · OH toward certain organic substrates, e.g. phenol and tryptophan. Our findings could lead to a deep revision of the present views of the role of bromide in saltwater photochemistry.