where 𝑘𝑘 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 is the rate constant for ZCuOCuZ formation, 𝑃𝑃 𝑖𝑖 is the partial pressure of species i, a and b represent the power-law dependence of rates on 𝑃𝑃 𝑂𝑂 2 and 𝑃𝑃 𝐻𝐻 2 𝑂𝑂 , respectively, and [𝐶𝐶𝐶𝐶(𝐼𝐼)] is the number of Cu(I) species. The conversions of O2 and H2O remain differential (< 1%) throughout the formation of ZCuOCuZ complexes, because these reactants are introduced with molar flowrates that greatly exceed the consumption of Cu(I) ions within the sample over the relevant timescales for ZCuOCuZ formation (1 -150 ks). As such, the rate of ZCuOCuZ formation can be stated in a form that reflects a pseudo-first-order dependence on [Cu(I)]