Infrared Spectra of Surface Metal Atom Vibrations. SNIFTIRS Studies in the Far Infrared Region Using Time Resolved FTIR Techniques

摘要

Studies of the vibrations of pure metals have historically been pursued by inelastic neutron scattering (which is sensitive to vibrations of the bulk crystal) and more recently by high-resolution electron energy loss spectroscopy. HREELS (which is more sensitive to vibrations of the metal surface). Direct infrared absorbance techniques provide advantages over both of these methods, since they may be used in more hostile environments (such as at the interface between metal and chemical solutions). They have rarely been applied with much success, however, because of the very effective shielding of the electromagnetic radiation by the metal conduction electrons. This results in an exponential damping of the radiation field as it enters the metal phase, with typical skin depths (1/e damping distances) of only a few tens of nm. This damping improves the sensitivity of infrared absorption measurements to the surface vibrations as opposed to bulk phonons, but limits the magnitude of the absorbance considerably. In this report we demonstrate that reflection infrared vibrational spectroscopy may be used to observe the vibrational structure of metallic species deposited on a metal surface which is under electrochemical control.