The response of the substrate on the catalyst surface depends on the relative dynamics of the system to the kinetics of the surface steps (i.e., reactions, desorption). For a catalyst oscillating between two states as a square waveform with amplitude of ΔU and frequency (f ~ τ -1 ), the optimum time-averaged turnover frequency will occur when the time scale of each state is approximately the same as the time scale of the individual surface steps. Referred to here as "surface resonance", the resonant frequencies depicted in Figure permit the surface coverage of B* to vary (θ min < θ B < θ max ) without stabilization before switching surface states.