Ionic clathrates from aqueous solutions detected with laser induced liquid beam ionization/desorption mass spectrometryIonic clathrates from aqueous solutions detected with laser induced liquid beam ionization/desorption mass spectrometry
Faculty of Sciences. Chemistry
International journal of mass spectrometry. - Amsterdam
185/187(1999), p. 271-279
Clathratelike structures of the alkali metal ions M+ = Li+, Na+, K+ Cs+, and ammonium with water molecules have been investigated with laser induced liquid beam ionization/desorption (LILBID) mass spectrometry. The LILBID process implies the desorption of ions from a thin jet of supercooled water in high vacuum by means of an IR laser pulse. Magic numbered water clusters are observed in the cation mass spectra of K+ and Cs+ halides, but not for Li+ and Na+. Predominant cluster sizes for K+ (H2O)n are n = 16, 20, 25, 27, and for Cs+(H2O)n, n = 18, 20, 22, 24, 27, 29, with the highest signal intensity for n = 20. Water clusters of this size correspond to deformed dodecahedral cage structures (clathrates) with a cation in the cavity, which are known to exist in the gas phase and in the solid state. The possible occurrence of clathratelike clusters in the liquid phase is discussed in the context of the physical chemistry of electrolyte solutions and the LILBID experiment.