Antimony is known to form well ordered epitaxial monolayers on clean cleaved (110) surfaces of III–V semiconductors like InP, GaP, and GaAs. These monolayers provide ideal candidates for photoelectron diffraction (PED) studies. At low photon energies (40–90 eV) the Sb 4d core level emission can be resolved into two chemically shifted spin-orbit split doublets indicative of the two distinct adsorption sites on the surface. The intensity of these two doublets together with that of the In 4d or Ga 3d subtrate emission was monitored as a function of polar angles and photon energy utilizing an ADES 400 photoelectron spectrometer at the BESSY TGM2 beamline. Strong variation of the intensity ratio of the doublets clearly demonstrates the usefulness of resolving chemical shifts. The experimental results are compared to theoretical calculations using the multiple-scattering cluster model including spherical-wave corrections for different adsorption models of the Sb monolayer.