Nonadiabatic Electron Transfer at Metal Surfaces

Abstract

The present article treats the role of the density of electronic states ρ_F at the Fermi level of a metal in affecting the rate of nonadiabatic electron transfer. The rate constant k_(ET) is calculated for the electron transfer across an alkanethiol monolayer on platinum and on gold. The ρ_F of platinum is about 7.5 times that of gold, the difference being mainly due to the d band of Pt. In spite of this difference, the electron transfer rate constant k_(ET) calculated in the present paper increases only by a factor of about 1.8, instead of the factor of about 7.5 expected using ρ_F alone. Implications of these results for present and past experiments are described. Bands which are weakly coupled (e.g., the d-band of Pt in the present case) contribute much less to the rate constant than is suggested by their density of states ρ_F. Thereby, k_(ET) is approximately independent of ρ_F in two cases: (1) adiabatic electron transfer and (2) nonadiabatic electron transfer when the extra ρ_F is due to the d electrons. Experiments which can test the latter are discussed.

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