Structure and ionization potentials of clusters containing heavy elements

Polyanionic Selenium Fragments and Vibrations in NaMSeNClusters

Density functional calculations on the series of clusters NaMSeNpredict different polyanionic selenium fragments depending on the relative amount of sodium. Calculations for Na2SeNclusters givee.g.horseshoe shaped polyanionic selenium chains that are accompanied by two Na atoms. The geometries obtained for NaMSe6clusters are changing from chains to Se2and Se3units highly dependent on the number of Na atoms. These clusters can be investigated experimentally by adding sodium atoms to selenium clusters in the reaction zone of a dual laser vaporization source and depositing them in a nitrogen matrix where they are investigated by Raman spectroscopy. An intense low frequency band between 165 and 225 cm−1is observed that can be attributed by a simple model of dynamical charge to certain vibrational modes with considerable changes of Na–Se bond lengths. The model spectra allow a quite good description of the low frequency Raman band.

Size-selective extended X-ray absorption fine structure spectroscopy of free selenium clusters

In a recent paper [M. Yao et al., J. Synchrotron Radiat. 8, 542 (2001)]], we proposed a new method for the size-selective EXAFS (extended x-ray absorption fine structure) of neutral-free clusters, in which not only the x-ray absorption process but also the deexcitation processes are utilized as the structural information. In order to verify this method experimentally, we have developed the synchronous measurements of EXAFS and photoelectron photoion coincidence and carried them out for a Se cluster beam by utilizing the third-generation intense x-ray source. The EXAFS spectra for Se small clusters have been obtained and compared critically with theoretical predictions.