Surface Photoelectric Effect and Orbital Symmetry: Evidence for Anomalous Dielectric Properties

Ultraviolet photoelectron spectra using He I resonance radiation and Ge(111) surfaces have been measured for both bonding and nonbonding orbitals. In all cases the partial photocurrent from a specific orbital is considerably enhanced for the macroscopic electric field normal to the surface independent of the orbital symmetry. This is interpreted in terms of an anomalous enhancement of the dielectric response due to surface polarization charge within the short electron escape depth (${\lambda }_e\lesssim 10$ Å) at these energies.