title: Ionization energies of argon clusters: a combined experimental and theoretical study.
abstract: We have measured appearance energies of Ar(n)+, n<or=30, by electron impact of gas phase clusters. Quantum-chemical calculations have been performed to determine the adiabatic and vertical ionization energies of argon clusters up to n=4 and 6, respectively. The experimental appearance energy of the dimer ion approaches, under suitable cluster source conditions, the adiabatic ionization energy. The agreement with values obtained by photoionization and threshold photoelectron-photoion coincidence (TPEPICO) spectra demonstrates that autoionizing Rydberg states are accessible by electron impact. Appearance energies of larger clusters, though, exceed the TPEPICO values by about 0.5 eV.
authors.affiliation: Institut für Ionenphysik, Leopold Franzens Universität, A-6020 Innsbruck, Austria. olof.echt@unh.edu
authors.forename: O
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authors.lastname: Echt
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authors.lastname: Fiegele
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authors.lastname: Rümmele
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authors.lastname: Probst
authors.forename: S
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authors.lastname: Matt-Leubner
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authors.lastname: Urban
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authors.lastname: Mach
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authors.lastname: Leszczynski
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authors.lastname: Scheier
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authors.initials: TD
authors.lastname: Märk