1. Institute of Physics, University of Neuchâtel, rue Emile-Argand 11, CH-2009 Neuchâtel, Switzerland, Department of Chemistry, Durham University, Durham, DH1 3LE, U.K., Swiss Norwegian Beamlines at ESRF, BP-220, 38043 Grenoble, France, and Laboratoire de Crystallographie, École Polytechnique Fédérale de Lausanne, BSP, CH-1015 Lausanne, Switzerland