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Abstract

We report on the experimental observation of the direct decay of a core vacancy in van der Waals clusters byemission of a fast electron from a neighboring atom. The process can be regarded as an interatomic Coulombicdecay of core holes (core-level ICD). We identify it unambiguously by electron-electron and electron-electron-photon coincidence spectroscopy of the decay of 2pvacancies in Ar clusters. While several earlier works reportedthe absence of this channel, we find core-level ICD to be of considerable significance and quantify the branchingratio of this nonlocal electron emission to conventional local Auger decay as (0.8±0.2)%. Our results aresupported by calculations on smaller clusters and show a reasonable agreement. This report on a successfullyperformed electron-electron-photon coincidence experiment provides a perspective for explorations of matterexposed to ionizing radiation. The observed core-level ICD is proposed to be of general importance for studieson charge redistribution after core-level photoionization where van der Waals clusters are often used as prototypesystems.