1. Fritz-Haber-Center for Molecular Dynamics, Hebrew University, Givat Ram, 91904 Jerusalem, Israel, B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, Skaryna Ave. 70, 220602 Minsk, Republic of Belarus, Institut für Chemie, Freie Universität Berlin, Takustrasse 3, D-14195 Berlin, Germany, and Institut für Mathematik, Freie Universität Berlin, Arnimallee 2-6, D-14195 Berlin, Germany