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

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Abstract
Equilibrium was established in both directions of the proton transferreaction O 2 H + + H 2 ⇄ H 3 + + O 2 proceeding in a flowing afterglow system. The equilibrium constantK was measured from equilibrium concentrations to be 1.05 ± 0.12 at 297°K. Limits to the rate constants were determined to be k forward ≥ 1.4 × 10−10 cm3 molecule−1 · sec−1 and k reverse ≥ 1.3 × 10−10 cm3 molecule−1 · sec−1. The value of K corresponds to a standard free energy change, Δ G 297 0 , of −0.03 +0.07 −0.06 kcal mole −1 and leads to a proton affinity difference P A (O2) − P A (H2) = + 0.002 ± 0.003 eV.