ABSORPTION SPECTRUM AND DECAY KINETICS OF O2- AND HO2 IN AQUEOUS SOLUTIONS BY PULSE RADIOLYSIS

The absorption spectrum and decay kinetics of O2- radical ions have been investigated in H2O2 and H2 + O2 solutions by the method of pulse radiolysis. The peak absorption at 2400-2450 Å has an extinction coefficient of 1970 M-1 cm-1. In the pH range ∼5 to 9.7, optical absorption assigned to O2- was observed. The decay of O2- absorption is consistent with k(HO2+O2-) = 7.9 × 107 M-1 sec-1. and k(O2-+O2-) < 105 M-1 sec-1. In the pH range below 5, absorption due to HO2 was also observed. The extinction coefficient of HO2 at 2400 Å was measured and equals 1150 M-1 cm-1. Using both our own data and those of Bielski and Schwarz recently reported results, we could account for both sets of data with k(HO2+HO2) = 6.7 × 105 M-1 sec-1. Both kinetic and spectroscopic results indicate that the pK of HO2 radicals may be slightly higher than the previously reported value of 4.5, namely 4.8.