Here, we use time-resolved in situ resonance Raman spectroscopy to measure the spectrokinetics of O2 activation over well-defined Cu-CHA materials that contain predominantly Cu either at 6-MR isolated or paired Al sites, or mixtures thereof. In situ Raman spectroscopy demonstrates that mono(μ-oxo)dicopper complexes form over extended periods (2 -6 h) similar to those needed to maximize CH3OH yields, which suggests the CuxOy complexes detected by Raman correspond to the Cu(II) species responsible for PMO. In contrast, in situ XAS measurements indicate that Cu(I) converts to Cu(II) intermediates (Cu-O2; e.g., μ-(η 2 :η 2 )peroxo dicopper) on much shorter timescales (< 0.3 h), and therefore, the Cu(I) to Cu(II) transformation detected by XAS may signify the formation of a precursor to PMO-active sites. The combination of DFT+U computed Raman intensities, steady-state Raman spectra, and O-labeling suggest ZCuOH sites activate O2 to form mono(μ-oxo)dicopper species. Rates of formation for the mono(μ-oxo)dicopper complex are measured as a function of O2 (5 -42 kPa O2) and H2O pressure (0 -1 kPa H2O) and temperature (648 -773 K) to probe the series of chemical transformations that occur during O2 activation. These rates depend on the isotopic substitution of water (kH/kD ≥ 2), which suggests that proton transfer may mediate O-O bond cleavage to form mono(μ-oxo)dicopper species. Collectively, these findings provide evidence for the molecular processes that determine the rates at which PMO-active sites form by interactions with O2 and H2O reactants.