1. a Research Laboratory for Crystal Physics , Hungarian Academy of Sciences , P.O. Box 132, H-1502 , Budapest , Hungary
2. b Chemical Laboratory , University of Kent , Canterbury, Kent , CT2 7NH , United Kingdom
3. c Universität Osnabrück, Fb. Physik , D-49069 , Osnabrück , Germany
4. d Department of Chemistry , University of Aberdeen , Aberdeen , AB9 2VE , United Kingdom