Generalized Ramsauer-Townsend resonance in angle-resolved photoemission extended fine-structure oscillations

We observe a resonance in the scattering amplitude for S(1s) photoelectrons from Ni atoms and interpret this resonance as a dip in the Ni atom partial cross section for electron scattering related to the Ramsauer-Townsend effect. This generalized Ramsauer-Townsend effect occurs at a particular energy and angle rather than in the total elastic cross section. We show that the resonance energy is sensitive to curved-wave corrections and, after including multiple-scattering effects, we derive the S---Ni bond length in c(2×{}2)S/Ni(100) from the angle-resolved photoemission extended fine-structure oscillations arising from the scattering of S(1s) photoelectrons off of nearest-neighbor Ni atoms in the presence of the generalized Ramsauer-Townsend resonance. We find this bond length to be 2.20±{}0.03 A{} corresponding to a S-Ni interplanar distance (d_⊥) of 1.32±{}0.04 A{}.