Electron ultrafast proton-coupled

This deuterium isotope effect cannot be explained by a purely electronic process but could be explained by a proton-coupled electron transfer. The population decay rate of the excited state at a fixed energy is successfully decomposed into two components an isotope independent solvation term and a proton-coupled electron transfer term with a marked deuterium effect. The latter terms for the CH3OH overlayer are found to be about twice those for the CH3OD overlayer. Thus, with time-resolved 2PPE, the ultrafast dielectric response of a protic/solvent metal-oxide interface has been revealed. 

Li, B., Zhao, J., Onda, K., Jordan, K.D., Yang, J. and Petek, H. (2006) Ultrafast interfacial proton-coupled electron transfer. Science, 311, 1436—1440. 

This Section addresses, in two sets of two chapters, two recent developments in proton transfer the ultrafast vibrational spectroscopic probing of the microscopic details of proton transfer in water and elsewhere, and the emergence of proton-coupled electron transfer reactions as a major reaction dass. 

PCET rate formalisms are cast primarily in terms of solvent coordinates for both the electron and proton, since both are charged particles that couple to the solvent polarization [5, 24]. In a concerted PCET reaction, the coupled transfer must occur via a common transition state and a common solvent configuration on both solvent coordinates. An ultrafast PCET reaction could be photoinitiated with resonant excitation, and a TOR probe would subsequently reveal the evolution of the two-dimensional reaction coordinate via the solvent response. Working in concert, these experiments would offer a powerful means to evaluate the coupling between the two coordinates in different types of PCET reactions and thus enable the PCET trajectories within the 2D space of Fig. 17.2 to be determined with much greater clarity. 

Ultrafast Interfacial Proton-Coupled Electron Transfer. ... 

Conical intersections (CIs) between electronic potential energy surfaces play a key mechanistic role in nonadiabatic molecular processes [1 ]. In this case the nuclear and electronic motions can couple and the energy exchange between the electrons and nuclei may become significant. In several important cases like dissociation, proton transfer, isomerization processes of polyatomic molecules or radiationless deactivation of the excited state systems [5,6] the CIs can provide very efficient channels for ultrafast interstate crossing on the femtosecond time scale. 

Proton transfer is a particularly important transport process. Beyond acid-base reactions, proton transfer may be coupled to electron transfer in redox reactions and to excited-state chemistry. It is of enormous significance in biochemical processes where it is an essential step in hydrolytic enzyme processes and redox reactions spanning respiration, and photosynthesis where proton motion is responsible for sustaining redox gradients. In relatively recent times, proton transfer in the excited state has undergone significant study, primarily fueled by advances in ultrafast spectroscopy. 

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