The reverse reaction rate re-forming βRO 2 in Figure is nonmonotonic, decreasing at higher energies. This is because the zero-point-corrected energies of βQOOH[O] and βRO2Isom are similar (differing by only 2 kJ/mol) and because βQOOH[O] has more freedom of motion than βRO2Isom. This causes the ratio of density of states between transition state and reactant to reach a peak around -60 kJ/mol. Because this isomerization is so fast, in the energy range from -60 kJ/mol through -10 kJ/mol, βRO 2 and βQOOH[O] equilibrate on a 10 ps timescale.