Singularity index of the core-level x-ray photoemission spectrum from surface atoms

We calculate the singularity index of the x-ray photoemission spectrum that is excited from a core level near a simple metal surface. Although the surface singularity index is generally different from the bulk singularity index, the former index has almost the same value as the latter. Moreover, using the Thomas-Fermi dielectric screening of point-charge-like core potentials, we investigate qualitatively the singularity index for physisorbed atoms.