1. a Institut fur Physikalische Chemie , TH-Darmstadt, Petersenstr. 20, D-6100, Darmstadt, FRG
2. b Institute of Physics, Jagellonian University , Reymonta 4, 30-059, Kraków, Poland
3. c Institute of Crystallography , USSR Acad. Sci., Leninsky Prosp. 59, 117333, Moscow, USSR