1. Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany, Service de Chimie Moléculaire, CEA/Saclay, F-91191 Gif-sur Yvette Cedex, France, Laboratoire LI2C, Université Pierre et Marie Curie, Boîte no. 51, 4 place Jussieu, 75252 Paris Cedex 05, France, and Department of Physical Chemistry, University of Florence, Cagliari, and Department of Applied Mathematics, Australian National University, via della Lastrucci 3, Sesto Fiorentino, 50019 Florence, Italy