TR3 spectra of various heme proteins studied and corresponding kinetics of the νFe-His mode during NO rebinding: Mb-H64V mutant (A), DHP (C), Cyt c (E), Hb (G), and the corresponding kinetics of the mode νFe-His (B, D, F, and H) calculated according to rate equations using time constants and yielding τD as in Table 1. The blue dashed curve in the lower panels represents the absorption kinetics to be compared to that of the mode νFe-His.