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)-O-center dot radicals formed upon photolysis of nitrate, before they leave the solvent cage. Bromide can thus inhibit the in-cage recombination between (OH)-O-center dot and (NO2)-N-center dot. The consequence is an increased generation of (NO2)-N-center dot and nitrite and of Br-2 (-center dot) + (OH)-O-center dot, compared to (OH)-O-center dot alone in the absence of bromide. We show that this effect compensates for the lower reactivity of Br (2) (-center dot) compared to (OH)-O-center dot 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.