1. JILA, National Institute of Standards and Technology, University of Colorado and Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309, USA
2. Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles, 50 av. F.D. Roosevelt, CP 160/09, 1050 Brussels, Belgium
3. Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands