1. Institute of Inorganic Chemistry, Rheinische Friedrich-Wilhelms-Universität, Gerhard-Domagk-Straße 1; Bonn D-53121 Germany
2. Mulliken Center for Theoretical Chemistry, Rheinische Friedrich-Wilhelms-Universität, Beringstr. 4; Bonn D-53121 Germany
3. School of Chemistry and Molecular Biosciences; University of Queensland, Brisbane St. Lucia; QLD 4072 Australia
4. Private Institute of Theoretical Chemical Physics, Via Dr. A. Sciarone Nr. 2; Muralto CH-6600 Switzerland