Potential Dependent Shift of Vibrational Frequencies of Carbon Monoxide Adsorbed on Platinum Group Metals:Stark Effect or Electron Back-Donation?

摘要

The stretching vibration of CO adsorbed on Pt and Pt-group metal electrodes shifts with the applied potential.The shift has been explained by Stark effect and/or electron back-donation from the electrode to the 2pi* anti-bonding orbital of CO.Stark effect assumes that the large potential drop at the interface affects molecular vibrations.If Stark effect is responsible,the rate of the spectral changes should be synchronized with the actual potential changes at the interface,i.e.double-layer charging.On the other hand,if the electron back-donation mechanism is responsible,the rate will be much faster than the double-layer charging.To define which mechanism is more responsible to the potential-dependent peak shift,we have examined the rate of the peak shift for potential modulations by surface-enhanced infrared absorption spectroscopy,in which the phase lag of the infrared response with respect to potential modulations is measured [1].