  We present experimental and theoretical results for the variation of the O 1s
intensity from a NiO(001) surface as the excitation energy is varied through
the Ni 2p1/2,3/2 absorption resonances, and as the incidence angle of the
radiation is varied from grazing to larger values. For grazing incidence, a
strong multi-atom resonant photoemission (MARPE) effect is seen on the O 1s
intensity as the Ni 2p resonances are crossed, but its magnitude decreases
rapidly as the incidence angle is increased. Resonant x-ray optical (RXRO)
calculations are found to predict these effects very well, although the
experimental effects are found to decrease at higher incidence angles faster
than those in theory. The potential influence of photoelectron diffraction
effects on such measurements are also considered, including experimental data
with azimuthal-angle variation and corresponding
multiple-scattering-diffraction calculations, but we conclude that they do not
vary beyond what is expected on the basis of the change in photoelectron
kinetic energy. Varying from linear polarization to circular polarization is
found to enhance these effects in NiO considerably, although the reasons are
not clear. We also discuss the relationship of these measurements to other
related interatomic resonance experiments and theoretical developments, and
make some suggestions for future studies in this area.
