The struggle for precise rate constants in gas phase reaction kinetics:: The reaction H+O2 ⇆ HO+O

A short sketch of the history over the last 100 years of the H-2-O-2-system in general and of the H + O-2 reversible arrow HO + O reaction in particular is given. Only after revision of the enthalpy of formation of OH in the year 2000, experimental and theoretical rate constant determinations approach an agreement within about 10 percent. Further improvements of the modeling depend on more precise thermochemical data for the reaction and on a detailed analysis of the contributions from all electronic states arising from the four open electronic shell species involved. Vibrational zeropoint energy problems of OH in classical trajectory calculations and detailed angular momentum couplings in adiabatic channel treatments have also to be mastered.