1. Department Chemie, Johannes Gutenberg-Universität Mainz 1 , Duesbergweg 10–14, D-55128 Mainz, Germany
2. Fachrichtung Chemie, Universität des Saarlandes 2 , D-66123 Saarbrücken, Germany
3. Hylleraas Centre for Quantum Molecular Sciences, Department of Chemistry, University of Oslo 3 , P.O. Box 1033, N-0315 Oslo, Norway
4. Theoretical Chemistry, Vrije Universiteit Amsterdam 4 , 1081HV Amsterdam, The Netherlands