1. Institute of Physical Chemistry, Polish Academy of Sciences, Department III, Kasprzaka 44/52, 01-224 Warsaw, Poland, Laboratoire de Physique de l'Ecole Normale Supérieure de Lyon, 69364 Lyon cedex 07, France, and Department of Mathematics and Natural SciencesCollege of Science, Cardinal Stefan Wyszyński University, Dewajtis 5, 01-815 Warsaw, Poland