Temperature Dependence of the Reaction OH + OH → H2O + O

Rate constants for the disproportionation reaction (1) OH + OH → H2O + O in the range 250–580 K have been measured by flash photolyzing H2O/N2 mixtures and monitoring the decay of OH using quantitative UV resonance spectrometry. The result k1 = (3.2 · 0.8) 10−12 exp (‐242/T) cm3/molecule · s, does not correlate with existing high temperature data and confirms previously suggested non‐Arrhenius behaviour for this reaction. On the basis of all available data the temperature variation of k1 over the range 250–2000 K is best represented by the empirical expression k1(T) = exp (‐27.73 + 1.49 · 10−3T) cm3/molecule · s. The extent of the Arrhenius graph curvature can be reconciled by a “close‐collision” model incorporating the energy variation of accessible product states.