A charged particle passing near a spherical body engenders real collective excitations which contribute to the stopping power. The greatest contributions occur at small impact parameters where many multipoles are excited on the spherical surface. An analytical form for these contributions is obtained for spheres that are sufficiently small that retardation is negligible and which are characterized by a spatially local, frequency-dependent dielectric function. Results are given for a variety of materials for which the optical-uv properties are known.

• Received 25 September 1986

DOI:https://doi.org/10.1103/PhysRevB.35.7365