1. University of Würzburg, Institutes of Physical and Organic Chemistry, Am Hubland, D-97074 Würzburg, Germany, Laboratoire de Chimie-Physique, Université Paris-Sud, Bât 349, F-91405 Orsay Cedex, France, and Laboratoire Francis Perrin, CEA/DSM/DRECAM/SPAM−CNRS URA 2453, DSM CEA Saclay, F-91191 Gif-sur-Yvette Cedex, France