1. Laboratoire de Chimie et Physique Quantiques, CNRS Université Toulouse III 118 route de Narbonne 31062 Toulouse France
2. Present address: Zernike Institute for Advanced Materials and Groningen Biomolecular Sciences and Biotechnology Institute University of Groningen Nijenborgh 4 9747 AG Groningen The Netherlands
3. Present address: MESA+ Institute for Nanotechnology University of Twente, P.O. Box 217 7500 AE Enschede The Netherlands
4. Department of Chemistry University at Buffalo, State University of New York Buffalo NY 14260-3000 USA
5. Hylleraas Center for Quantum Molecular Sciences Department of Chemistry University of Oslo Oslo Norway