1. Instituto de Quimica, Universidade Federal de Goias, Goiania GO 74001-970, Brazil, Instituto de Fisica, Universidade de Brasilia, Brasilia DF 70910-900, Brazil, Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland, and Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan, Poland