1. 1Institutt for fysikalsk kjemi, Norges tekniske høgskole, N-7034 Trondheim-NTH, Norway
2. 2Department of Chemistry, University of Aberdeen, Old Aberdeen, AB 9 2UE, Scotland
3. 3Institut für Anorganische Chemie, Technische Universität Clausthal, D-3392 Clausthal-Zellerfeld, FRG