1. J. W. Goethe -University Frankfurt/M., Institute of Physical and Theoretical Chemistry, Max-von-Laue-Strasse 7, D-60438 Frankfurt/M, Germany, J. W. Goethe -University Frankfurt/M., Institute of Biophysics, Max-von-Laue-Strasse 1, D-60438 Frankfurt/M, Germany, TU Dresden, Physical Chemistry/Electrochemistry, Bergstr. 66b, D-01062 Dresden, Germany, and Universidade de Vigo, Departamento de Quimica Fisica, Campus Universitario, 36310 Vigo, Spain