Using angle- and energy-resolved photoyield spectroscopy, we investigate the properties of the multipole plasmon excitation. At higher energies, a systematic dependence of the photoyield on the photon angle of incidence is observed and explained on the basis of classical Fresnel theory, indicating the possibility of obtaining information about optical constants from such measurements. A feature above the multipole plasmon is assigned to the excitation of a bulk plasmon by the photon field.

• Received 9 February 1998

DOI:https://doi.org/10.1103/PhysRevB.58.R4285