Localized versus delocalized excitations just above the 3d threshold in krypton clusters studied by Auger electron spectroscopy.
ABSTRACT We present Auger spectroscopy studies of large krypton clusters excited by soft x-ray photons with energies on and just above the 3d(52) ionization threshold. The deexcitation spectra contain new features as compared to the spectra measured both below and far above threshold. Possible origins of these extra features, which stay at constant kinetic energies, are discussed: (1) normal Auger process with a postcollision interaction induced energy shift, (2) recapture of photoelectrons into high Rydberg orbitals after Auger decay, and (3) excitation into the conduction band (or "internal" ionization) followed by Auger decay. The first two schemes are ruled out, hence internal ionization remains the most probable explanation.
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ABSTRACT: X-ray absorption spectra of small krypton clusters with average size of ∼15 atoms were measured with Kr2+ ion yields at the Kr 3d5/2 and 3d3/2 region. The second lowest Rydberg transition 3d−16p is redshifted from the corresponding atomic transition, and shows an asymmetric broad shoulder feature. This characteristic feature is attributable to some surface sites with different coordination numbers such as corner, edge and face as previously observed in the Kr 3d photoexcitation and photoelectron spectra. Diffuse Rydberg states are influenced predominantly with induced polarization of the surrounding atoms. On the other hand, the lowest transition 3d−15p is blueshifted, and shows a rather narrow peak. The blueshift arises from short-range repulsive interaction, that is, exchange interaction of the Rydberg electron with the surrounding atoms. The larger coordination number of the nearest neighbor atoms increases both the exchange (blueshift) and induced polarization (redshift) effects. In the higher Rydberg state, the blueshift effect is drastically reduced but the redshift effect is most dominant. Cancelation of these two effects can be expected in the lowest Rydberg transition. The present experimental analysis enables us to discuss the site-dependent and state-dependent exchange interaction.Journal of Electron Spectroscopy and Related Phenomena 11/2008; 166(1):16-20. DOI:10.1016/j.elspec.2008.07.010 · 1.55 Impact Factor
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ABSTRACT: Surface-site resolved Kr 3d5/2−15p and 3d5/2−16p and Xe 4d5/2−16p and 4d5/2−17p Rydberg excited states in small van der Waals Kr and Xe clusters with a mean size of 〈N〉=15 are investigated by X-ray absorption spectroscopy. Furthermore, surface-site resolved Kr 4s−25p, 4s−26p, and 4s−14p−15p shakeup-like Rydberg states in small Kr clusters are investigated by resonant Auger electron spectroscopy. The exchange interaction of the Rydberg electron with the surrounding atoms and the induced polarization of the surrounding atoms in the singly and doubly ionized atoms are deduced from the experimental spectra to analyze different surface-site contributions in small clusters, assuming that the corner, edge, face, and bulk sites have 3, 5–6, 8, and 12 nearest neighbor atoms. These energies are almost proportional to the number of the nearest neighbor atoms. The present analysis indicates that small Kr and Xe clusters with 〈N〉=15 have an average or mixture structure between the fcc-like cubic and icosahedron-like spherical structures.Journal of Electron Spectroscopy and Related Phenomena 01/2011; 183(1):29-35. DOI:10.1016/j.elspec.2010.07.007 · 1.55 Impact Factor