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Determination of Ionization Energies of Small Silicon Clusters with Vacuum Ultraviolet Radiation

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journal contribution
posted on 2010-03-11, 00:00 authored by Oleg Kostko, Stephen R. Leone, Michael A. Duncan, Musahid Ahmed
In this work we report on single photon vacuum ultraviolet photoionization of small silicon clusters (n = 1−7) produced via laser ablation of Si. The adiabatic ionization energies (AIE) are extracted from experimental photoionization efficiency (PIE) curves with the help of Franck−Condon simulations, used to interpret the shape and onset of the PIE curves. The obtained AIEs are (all energies are in eV) Si (8.13 ± 0.05), Si2 (7.92 ± 0.05), Si3 (8.12 ± 0.05), Si4 (8.2 ± 0.1), Si5 (7.96 ± 0.07), Si6 (7.8 ± 0.1), and Si7 (7.8 ± 0.1). Most of the experimental AIE values are in good agreement with density functional electronic structure calculations. To explain observed deviations between the experimental and theoretical AIEs for Si4 and Si6, a theoretical search of different isomers of these species is performed. Electronic structure calculations aid in the interpretation of the a2Πu state of Si2+ dimer in the PIE spectrum. Time-dependent density functional theory calculations are performed to reveal the energies of electronically excited states in the cations for a number of Si clusters.