Evolution of the charge localization process in xenon cluster ions: From tetramer to dimer cores as a function of cluster size.

The charge localization process in Xe+N cluster ions (N=40– 20 000) is investigated with fluorescence spectroscopy methods. New discrete and continuous luminescence bands in the visible and near infrared spectral range are observed and are assigned to radiative transitions of ionic dimers, trimers and tetramers inside Xe clusters. The bands are related to the 5p5 2P1/2 →5p5 2P3/2 transition of electronically excited atomic Xe ions and the 6p→6s transitions of electronically excited Xe neutrals. The dependence of the size of the ionic centers on the Xe cluster size is discussed. In large clusters discrete lines are due to embedded dimer emission and they are identified as 2(1/2)u→1(3/2)g transitions between different vibrational levels. Line positions are blue-shifted by 30 (→±1) meV with respect to free molecular dimer ions. The energy shift is due to the interaction of the surrounding neutral Xe cluster atoms with the embedded ionic Xe molecules.