A phenomenon of partial localization of core holes has been discovered. Fourth-order Green's function and large-scale configuration interaction calculations have been carried out on the N 1s x-ray photoelectron spectrum ͑XPS͒ of a linear NiN 2 cluster. The N 1s core holes in the ionized states of the cluster are to varying extent delocalized between the two geometrically inequivalent nitrogen atoms. In some of the states the core holes are significantly delocalized. Good agreement with the

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... imental spectra of the N 2 /Ni(100)c(2 ϫ2) chemisorption system is obtained, which makes clear that the effect is to be expected also in this solid-state system. The partial localization of core holes leads to distinct interference effects in the angularly resolved XPS. This can be used for the experimental detection of the effect. The effect is more pronounced for NiP 2 , which is also studied here.