Kinetic Isotope Effect on Electron Transfer Rates Across Self-Assembled Monolayers: A Case for Quantum Effects

Long range ET across several self-assembled mon-olayer (SAM) covered Au electrodes is investigated using protonated and deuterated thiols (RSH/RSD). The rate of tunneling is measured using both chronoamperometry and cyclic voltammetry and it shows a prominent KIE. The KIE is ~2 (normal) for medium chain length thiols where the Tafel plot indicate substantial through space tunneling and is ~0.25 (inverse) for long chain thiols where the Tafel plot indicate mostly through bond tunneling. These results imply substantial contribution from the classical modes at the Au-(H)SR interface, which shift substantially on deuteration of the thiols, to the ET process.