The effect of surface interband transitions (SIT) on surface plasmon dispersion was investigated by high-resolution electron-energy-loss spectroscopy for Ag(001). We demonstrate that the anomalous linear dispersion on this face, which is at variance with the parabolic form present for the other low Miller index surfaces, is due to a SIT between Shockley states that nearly matches the surface plasmon frequency. The anomaly is eliminated when the substrate undergoes a missing-row reconstruction induced by oxygen adsorption that removes the SIT.

• Received 16 December 1999

DOI:https://doi.org/10.1103/PhysRevB.61.7324