[1] Univ Barcelona, Dept ECM, Fac Fis, Barcelona 08028, Spain
[2] Univ Barcelona, IN2UB, Barcelona 08028, Spain
[3] Calif State Univ Northridge, Dept Chem & Biochem, Northridge, CA 91330 USA
[4] Swiss Fed Inst Technol Lausanne EPFL, Lab Theoret Phys Chem, Inst Sci & Ingn Chim, CH-1015 Lausanne, Switzerland