Figure 3.

Reaction between MV-CcO and O₂ at 20^oC. Difference Raman spectra were calculated at the indicated times after initiation of the reaction between MV-CcO and O₂ by subtracting the spectrum recorded with ¹⁸O₂ as a substrate from that obtained with ¹⁶O₂. All porphyrin vibrations cancel in the difference spectra, whereas vibrations of bound oxygen appear as derivative-shaped features. Full scale of the ordinate axis is 28% of the porphyrin ν₇ mode in the absolute spectra. Each trace is an average of several isotope-difference spectra (1–1.5 × 10⁶ shots per isotope total) obtained in independent experiments.