TOFs are computed at fixed N 2 , O 2 , N and O presssures and at zero conversion. N radical densities are estimated from N 2 dissociation fractions measured at similar plasma conditions and O 2 dissociation fractions assumed to be one order of magnitude greater than N 2 . 27-31 N 2 and O 2 are assumed to have the same vibrational temperature, and the vibrational energy distributions and the consequent effects on the kinetics of N 2 and O 2 dissociative adsorption are modeled following Mehta et al (Supplementary Methods and Supplementary Fig. ). Fig. compares TOFs at a Pt step as a function of conditions. Thermal TOFs (black line) over Pt(211) increases with T but are vanishingly small at even the highest temperature.