ULTRAFAST MEASUREMENTS ON DIRECT PHOTOINDUCED ELECTRON-TRANSFER IN A MIXED-VALENCE COMPLEX

A direct measurement of the kinetics of intramolecular photoinduced metal-metal charge transfer has been made, i.e. [GRAPHICS] where the solvent is H2O or D2O and k(ET) signifies the reverse-electron-transfer (ET) rate coefficient. The apparent reverse-electron-transfer kinetics are nonexponential with a limiting rate constant, k(lim) = k(t) where t --> infinity, equal to (8 +/- 3) x 10(11) s-1. This is close to the theoretical predictions from the model of Sumi and Marcus (classical vibrational modes), k(ET,SM) = 10(13) and 5 x 10(12) s-1, and from the model of Jortner and Bixon (quantum mechanical vibrations), k(ET,JB) = 1.2 x 10(12) s-1. The parameters required for these theories were estimated by resonance Raman spectroscopy, static absorption spectroscopy, and recently published transient Stokes shift measurements.