Laser-Induced Potential Jump at the Electrochemical Interface Probed by Picosecond Time-Resolved Surface-Enhanced Infrared Absorption Spectroscopy

Picosecond time-resolved surface-enhanced infrared absorption spectroscopy (SEIRAS) has been used for the first time to examine the potential jump at the electrochemical interface induced by a visible pulse irradiation. The potential dependent shift of the C−O stretching vibration of CO adsorbed on a Pt electrode was utilized to monitor the potential jump. A 6-cm^-1 red-shift was observed with a time delay of ∼200 ps with respect to a visible pump-pulse irradiation (532 nm, 35 ps duration, 3 mJ cm^-2). The observed red-shift is ascribed to the heating of the in-plane frustrated translational mode of CO and the negative shift of potential. These two contributions can be separated with the aid of the transient of the background reflectivity of the electrode surface. The heating of water layers near the surface is mainly responsible for the potential jump through the orientation change of water molecules. This method is promising as a tool to examine ultrafast electrode dynamics.