1. Département de Chimie Physique, Université de Genève, 30, quai E. Ansermet, CH1211 Geneva 4, Switzerland, Laboratoire de Cristallographie, Université de Genève, 24 Quai Ernest Ansermet, CH1211 Geneva 4, Switzerland, Physics department, Institute for Energy Technology, P.O. Box 40 NO-2027 Kjeller, Norway, and University of Hawaii at Manoa, Department of Chemistry, 2545 The Mall, Honolulu, Hawaii 96822-227