Electronic and geometric structure of doped rare-gas clusters:
surface, site and size effects studied with luminescence spectroscopy |
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Authors: | R von Pietrowski K von Haeften T Laarmann T Möller L Museur A V Kanaev |
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Institution: | 1. Hamburger Synchrotronstrahlungslabor HASYLAB at Deutsches Elektronen Synchrotron DESY, Notkestr. 85, 22603, Hamburg, Germany 2. Lehrstuhl für Physikalische Chemie II, Geb?ude NC, Raum 7/33, Ruhr-Universit?t Bochum, Universit?tsstr. 150, 44780, Bochum, Germany 3. Max-Born Institute, Max-Born str. 2a, 12489, Berlin, Germany 4. Institut für Atomare Physik, Technische Universit?t Berlin, Hardenbergstr. 36, 10623, Berlin, Germany 5. Laboratoire de Physique des Lasers LPL, CNRS, Institut Galilée, Université Paris-13, 93430, Villetaneuse, France 6. Laboratoire d'Ingénierie des Matériaux et des Hautes Pressions LIMHP, CNRS, Institut Galilée, Université Paris-13, 93430, Villetaneuse, France
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Abstract: | The electronic and geometric structure of rare gas clusters doped with
rare-gas atoms Rg = Xe, Kr or Ar is investigated with fluorescence excitation
spectroscopy in the VUV spectral range. Several absorption bands are
observed in the region of the first electronic excitations of the impurity
atoms, which are related to the lowest spin-orbit split atomic 3P1
and 1P1 states. Due to influence of surrounding atoms of the
cluster, the atomic lines are shifted to the blue and broadened
(“electronical cage effect”). From the known interaction potentials and
the measured spectral shifts the coordination of the impurity atom in
ArN, KrN, NeN and HeN could be studied in great detail.
In the interior of KrN and ArN the Xe atoms are located in
substitutional sites with 12 nearest neighbours and internuclear distances
comparable to that of the host matrix. In NeN and HeN the cluster
atoms (18 and 22, respectively) arrange themselves around the Xe impurity
with a bondlength comparable to that of the heteronuclear dimer. The results
confirm that He clusters are liquid while Ne clusters are solid for N≥
300. Smaller Ne clusters exhibit a liquid like behaviour. When doping is
strong, small Rgm-clusters (Rg = Xe, Kr, Ar, m≤10 2) are formed
in the interior sites of the host cluster made of Ne or He. Specific
electronically excited states, assigned to interface excitons are observed.
Their absorption bands appear and shift towards lower energy when the
cluster size m increases, according to the Frenkel exciton model. The
characteristic bulk excitons appear in the spectra, only when the cluster
radius exceeds the penetration depth of the interface exciton, which can be
considerably larger than that in free Rgm clusters. This effect is
sensitive to electron affinities of the guest and the host cluster. |
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Keywords: | 36 40 -c Atomic and molecular clusters 36 40 Mr Spectroscopy and geometrical structure of clusters 73 20 -r Electron states at surfaces and interfaces |
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