1. Department of Physical and Analytical Chemistry, Uppsala University, P.O. Box 579, SE-751 23 Uppsala, Sweden, Physical Chemistry 1, Lund University Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden, and Physics Department, Sao Paulo State University, Sao Jose do Rio Preto, Sao Paulo, Brazil