1. Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany
2. Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany
3. Laboratoire de Chimie Physique Moléculaire, Swiss Federal Institute of Technology Lausanne (EPFL), 1015
Lausanne, Switzerland
4. CNR Istituto di Metodologie Inorganiche e dei Plasmi, CP10, 00016 Monterotondo Scalo, Italy
5. CIMAINA and Dipartimento di Fisica, Università di Milano, 20133 Milano, Italy
6. Department of Physics, University of Trieste, 34128 Trieste, Italy
7. Elettra-Sincrotrone Trieste, 34149 Basovizza, Trieste, Italy