1. J. Heyrovsky Institute of Physical Chemistry, v.v.i, Academy of Sciences of the Czech Republic, Dolejškova 3, CZ-18223-Prague 8, Czech Republic, Institute of Inorganic Chemistry, v.v.i., Academy of Sciences of the Czech Republic, CZ-250 68 Rez near Prague, Czech Republic, ESRF Grenoble, 38043 Grenoble Cedex, France, and Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, Swiss Federal Institute of Technology, CH-1015 Lausanne, Switzerland