Extended Data Figure 4. A comparison of the electronic absorption spectra of compound T (red trace) and MMOH^red (blue trace).

T exhibits an absorption band in the near-ultraviolet region, giving rise to its resonance Raman enhancement. Single wavelength time courses of the reaction of 25 μM MMOH^red/MMOB with a 450 μM solution of CH₄ and 450 μM O₂ at 4 °C, pH 7 were recorded throughout the visible region (concentrations after mixing). The absorbance at each wavelength at the time of maximal T formation given by the speciation plot shown in Extended Data Fig. 1b was extracted and used to make the red trace shown.