where r f 3 RB * is the rate of 3 RB * formation and γ1 O 2 is the singlet oxygen formation yield for the reaction between 3 RB * and dissolved O 2 . Insertion of eq 7 into the rate law of O 2 consumption, eq 6, leads to eq 8 that we use here to interpret the observed reaction order. )) in experiments with histidine (His, red circles), tyrosine (Tyr, blue triangles), and methionine (Met, yellow squares) performed under similar experimental conditions (see entries 10-11, 14-15, and 18-21 in Table ).