Determination of the proton affinity from the kinetics of proton transfer reactions. IV The equilibrium O2H++H2⇄ H3++O2 and the relative proton affinity of O2 and H2

Equilibrium was established in both directions of the proton transfer reaction O2H++H2⇄ H3++O2 proceeding in a flowing afterglow system. The equilibrium constant K was measured from equilibrium concentrations to be 1.05 ± 0.12 at 297°K. Limits to the rate constants were determined to be kforward ≥ 1.4 × 10−10 cm3 molecule−1 · sec−1 and kreverse ≥ 1.3 × 10−10 cm3 molecule−1 · sec−1. The value of K corresponds to a standard free energy change, Δ G2970, of −0.03+0.07−0.06 kcalmole−1 and leads to a proton affinity difference P A (O2) − P A (H2) = + 0.002 ± 0.003 eV.