Fig. 2.

Difference spectra {[(L^H)Cu^I(X)]⁺ - [(L^H)Cu^I(CO)]⁺} recorded after 355 nm excitation of [(L^H)Cu^I(CO)]⁺ in tetrahydrofuran at 198 K under a 1 atm mixture of O₂:CO = 7:3. The spectra were recorded at differing delay times: (a, top). 0 to 2 μs where [(L^H)Cu^I(thf)]⁺ (λ_max, 333 nm) converts to a mixture of [(L^H)Cu^I(CO)]⁺ and [(L^H)Cu^II(O₂^•−)]⁺ (λ_max, 425 nm): squares (black spectrum), 0 μs; circles (red spectrum), 0.5 μs; diamonds (blue spectrum), 2.0 μs. The inset is an absorption transient monitored at 425 nm with a superimposed first-order fit (red), k_obs = 3.0 × 10⁶ s⁻¹ and (b, bottom), 2 μs to 40 ms where [(L^H)Cu^II(O₂^•−)]⁺ converts to [(L^H)Cu^I(CO)]⁺: squares (black spectrum), 2 μs; circles (red spectrum) 5 ms; diamonds (blue spectrum), 20 ms. The inset is an absorption transient monitored at 425 nm with a superimposed first-order fit, k_obs = 130 s⁻¹. The spectrum shown in solid green is that calculated as {Abs[(L^H)Cu^II(O₂^•−)]⁺ - Abs [(L^H)Cu^I(CO)]⁺}. Figure adapted from reference 42.