1. Institute of Experimental Physics, Warsaw University, Hoża 69, 00-681 Warszawa, Poland
2. Institute of Theoretical Physics, Warsaw University, Hoża 69, 00-681 Warszawa, Poland
3. Dept. of Chemistry, Warsaw Univ. of Technology, Pl. Politechniki 1, 00-661 Warszawa, Poland
4. Inorganic Chemistry Dept., Dortmund University, 44221 Dortmund, Germany