Dirhodium (II,III) caprolactamate visible spectrum as a function of time (1, 3, 5, and 7 h): TBHP (0.27 M) in DCE with 1.0 mol % Rh2(cap)4 without olefinic substrate. Note that dirhodium (II,III) caprolactamate (λmax 507 and 974 nm) is clearly visible even after 5 h and that dirhodium (II,II) caprolactamate (λmax 607 nm) becomes visible as the reaction proceeds.