Direct and Superexchange Mechanisms for Optical and Thermal Electron Transfer and the Detectability of the Transition State by Radiative Spectral Emission

Abstract

We have reviewed a number of correlations between kinetic parameters which characterize optical and thermal electron transfer between two molecular sites. The correlations involve directly observables such as the molar absorptivity and emitted spectral distribution for optical and the rate constants for the thermal processes. We have also discussed the possible direct optical detection of the transition state configuration. This is feasible in principle by emission or Raman scattering from the first excited state in the adiabatic limit. The correlations can be extended both to optical and thermal electron transfer between metal or semiconductor electrodes and depolarizer molecules or molecular adsorbates, and to electron transfer in three-level, superexchange systems. In the latter case relations between superexchange rate constants and Raman scattering profiles can be pointed out.

Key Words:

• intervalence transitions
• superexchange
• transition state
• Raman scattering