FLASH PHOTOLYSIS STUDY OF MECHANISM OF OZONIDE ION DECAY IN BASIC AQUEOUS HYDROGEN PEROXIDE

A study has been made at 27 ± 2° of the rate of decay of the 4300-Å absorption peak of the ozonide ion produced by the flash photolysis of hydrogen peroxide in aqueous alkaline solutions. The observed decay in every case followed the course of a first-order reaction. The rate constants increased with increase in H2O2 concentration and decreased with increase in the concentration of base and dissolved molecular oxygen. A longer lived species was formed in part at the same rate as the ozonide decayed. Spectral and kinetic evidence suggests that this longer lived species is ozone. The main reactions explaining the results are O3- →k1 O2 + O-, O2 + O- →k2 O3-, O- + HO2- →k3 O2- + OH-, and O3- + O2- →HOH O3 + HO2- + OH- for which k1 = 2.81 ± 0.14 × 103 sec-1 and k2/k3 = 3.6 (±0.3). The marked increase in stability of O3- at high (NaOH) can be explained on the basis of the formation of the ion pair: Na+ + O3- = NaO3, the equilibrium constant for which is 2.24 ± 0.11 M-1.