1. Laboratoire de Spectrométrie Physique, CNRS UMR 5588, Joseph Fourier University Grenoble, B.P. 87, 38402 St. Martin d'Hères, France; LCPO CNRS-ENSCPB (UMR 5629), Bordeaux 1 University, 16 Avenue Bey-Berland 33607 Pessac France; Instituto de Química, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500 CEP91501-970-Porto Alegre-RS, Brazil; and Cermav-CNRS, B.P. 53, 38041 Grenoble Cedex 9, France