1. CEA Marcoule, DCC/DRRV/SEMP Laboratoire de Chimie Théorique et Structurale, 30207 Bagnols sur Cèze Cedex, France, Chemistry Department, University of Reading, Whiteknights, Reading RG6 6AD, U.K., Institute of Physical Chemistry of the Russian Academy of Sciences, 31 Leninsky Prosp., Moscow, Russia, CEA Saclay, DCC, 91191 Gif-sur-Yvette Cedex, France, and CEA Saclay, DSM/DRECAM/SCM (CNRS URA 331), 91191 Gif-sur-Yvette Cedex, France