Hannover 2003 – scientific programme
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MO: Molekülphysik
MO 12: Poster II
MO 12.7: Poster
Thursday, March 27, 2003, 16:00–18:30, Lichthof
Ionization energies and spatial volumes of the singly occupied molecular orbital in hydrated magnesium clusters [Mg,nH2O]+ — •Bjoern Reinhard and Gereon Niedner-Schatteburg — Fachbereich Chemie, Technische Universitaet Kaiserslautern, 67663 Kaiserslautern, Germany
The vertical and adiabatic ionization energies (VIEs and AIEs) as well as the spatial volumes of the singly occupied molecular orbital (SOMO) of [Mg,nH2O]+, n<20, were determined by ab initio calculations. Ionization energies were evaluated from Koopmans’ theorem and explicitly as differences of the total energies of [Mg,nH2O]+ and [Mg,nH2O]2+ as obtained by Hartree-Fock, post-Hartree-Fock and gradient corrected density functional (DFT) methods. In the case of clusters with a 6-fold coordinated magnesium cation [Mg(H2O)6,(n-6)H2O]+ Koopmans’ theorem fails for n=6-8,10. In contrast this is a valid approximation for all other cluster sizes. The most stable isomers of [Mg,nH2O]+, n=6-9, exhibit significantly enhanced SOMO volumes. This coincides with a significant drop in ionization energies and with an increase in electron correlation. In these clusters Koopmans’ theorem is a crude approximation due to the neglect of electron correlation. The cluster size dependency of orbital relaxation and change in electron correlation upon ionization allows for an analytical fit in terms of the spatial SOMO volume. Reorganization energies and SOMO volumes indicate strong structural changes in the clusters during ionization due to a significant localization of the SOMO in [Mg,nH2O]+, n<6 and n>8.