Electrochemical potential dependence of an ultrafast nonequilibrium electron dynamics at Au(111) electrode/aqueous solution interfaces modified with alkanethiols

Femtosecond transient reflectivity measurements were performed for Au(111) electrode/aqueous solution interfaces under electrochemical potential control. Electrode interfaces modified with and without a self-assembled monolayer of alkanethiols were studied in aqueous solutions of HClO₄ and H₂SO₄. Dependence on electrochemical potential, interface modification, and kind of solute anions are observed concerning the transient reflectivity response in 3ps. For Au electrodes in an aqueous HClO₄ solution, the rate of the initial relaxation at an unmodified interface, 6-10 ps^-1, decreased with the electrochemical potential at the potential range where a water dipole rearranged. The rate for alkanethiol-modified interfaces showed a tendency depending on the hydrocarbon chain length. A relative deposited energy from absorbed photon energy was estimated, indicating that interface modification with alkanethiols restricted energy dissipation from the interface. Our trial could contribute not only to develop a study of interaction between a substrate and adsorbed molecules in an ultrafast time scale but also to elucidate elementally processes of electrochemical reactions such as oxidation/reduction reactions at an electrode interface.