The oxidation of HI at low temperatures and the heat of formation of HO2

The kinetics of the oxidation of hydrogen iodide (HI + O2) at low temperature (414–499 K) in the gas phase by the method of iodination kinetics is complicated by a heterogeneous reaction between hydrogen iodide and oxygen. Present work leads to an upper limit for the bimolecular rate constant k1 for the first and rate‐determining step equation image These data are combined with an estimated A factor A1 = 109.3±0.2 L/mol·s (assuming a tight linear I···H···O— transition state), to calculate the lower limit of the activation energy for the forward reaction E1. This leads to a minimum value for the heat of formation of the HO2 radical, ΔHf298°(HO2) < 3.0 kcal/mol.