Detection of Singlet Oxygen in Radiolysis of Aerated Aqueous Solutions

Abstract— The detection of singlet oxygen ( 1 O 2 ) in the γ‐radiolysis of air saturated aqueous solutions may be achieved by using a selective method under such conditions that other strongly reactive intermediates such as −OH radicals do not react or are prevented from giving the same reaction. Since all or most 1 O 2 acceptors also react with −OH radicals, the elimination of OH radicals with appropriate scavengers may be necessary. A recently developed method for the detection of 1 O 2 in neutral aqueous solutions based on the bleaching of p ‐nitrosodimethylaniline (RNO) in a solution containing an imidazole derivative, has been used in this work to detect 1 O 2 in γ‐radiolysis. In the system imidazole + RNO, the reaction between 1 O 2 and imidazole produces a trans ‐annular peroxide which leads to the bleaching of RNO. The bleaching of RNO depends in a characteristic way on the concentration of different imidazole derivatives at high concentrations. This dependence is the same in certain photolysis experiments (where only 1 O 2 reacts in this way) and in radiolysis. The bleaching of RNO, as induced by the reaction between 1 O 2 and imidazoles, is also observed in the presence of ethanol which scavenges all −OH radicals but does not react with 1 O 2 or trans ‐annular peroxide. Moreover, in the absence of imidazole, the addition of ethanol to a dilute solution of RNO protects it completely against −OH radical attack. Thus, the results of these experiments indicate that 1 O 2 may be formed in the radiolysis of air saturated aqueous solutions in a relatively low yield G( 1 O 2 ) ∼ 0.1–0.3.