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International audience; A method for spectroscopic characterization of free ionic clusters and nanoparticles utilizing X-ray synchrotron radiation is presented. We demonstrate that size-selected ammonium bisulphate cluster ions, NH4+(NH4HSO4)(n), captured in a linear ion trap, exhibit well-defined core-level absorption edges in the reconstructed fragment-ion abundance spectra. In addition to the specific photo-fragmentation pathways observed at the N1s-, O1s- and S2p-edges, dissociation also occurs as a consequence of clusters colliding with helium present as buffer gas in the ion trap. Separate off-beam experiments were conducted to establish the activation kinetics of these collision induced dissociation processes. Furthermore, it is demonstrated that the electrons released upon photoionization of background helium are too few in number to produce multiply charged cluster ions, and thereby induce fragmentation of the salt clusters, to any significant degree. The mechanisms for photon absorption and subsequent cluster fragmentation are analysed and discussed. In addition to its inherent element specificity, the method holds promise for cluster structure elucidation resulting from the sensitivity of the near edge absorption structure to the local chemical environment of the excited atom.

The changes in lattice and molecular structure of the dodecatungstophosphoric acid hexahydrate (WPA-6) induced by the temperature treatment between 244 and 373 K, were studied in situ by X-ray powder diffraction and Raman spectroscopy. The increase in temperature was followed with the slight modifications of Keggin's anion, expansion of the unit cell and an abrupt change in the crystallite microstructure of WPA-6 what was monitored by the Rietveld and Warren-Averbach methods. Those two discontinuities in the thermal expansion of 4 0 0 interplanar spacing, observed at about 320 and 340 K, are result of the non-convergent reversible phase transition, produced by partial reduction and oxidation of the tungsten, known as an ion with mixed valence. The extraordinary compression of P-Oa bond length [1.61(1) angstroms at 298 K and 1.44(2) angstroms at 373 K], broadening and splitting of V1(P-Oa) bond with the increase in temperature, the abrupt change of crystallite dimension and the strain at 338 K, indicate a modification in the charge distribution followed with the partial reduction of W6+ into W5+ ions (i.e. 'heteropoly blue' formation). The partial reduction is closely related to the change in a dynamic equilibrium between different proton species and hydrated proton entities, such as oxonium H3O+, dioxonium H5O2+, triaquaoxonium H7O3+, etc.