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[en] Today's knowledge about gas phase cluster ions originates mostly from very recent studies. This review summarizes first the potential role of clusters in many fundamental and applied fields and the unique position of clusters between the gaseous and solid state of matter. Then several exciting recent discoveries in cluster physics are discussed. Finally, ionization and concomitant fragmentation of clusters are reviewed in detail, including ionization processes and mechanisms, ionization efficiency, stability of singly and multiply charged ions and the subject of magic numbers. 107 refs.; 2 figs
[en] Highlights: • Quantum defects for observed resonances in H2 above the (1s,3l) limit are reported. • The quantum defects are compared to those calculated for theoretical energies. • Continuity of the state vibrational series through the n = 3 threshold is shown. • Despite extensive vibronic coupling, vibrational motion is predominantly diabatic. Heavy Rydberg behaviour and absolute quantum defects are reported for resonances in the ungerade manifold of H2 above the dissociation limit. The continuity of the vibrational progression of the state through the crossing with the asymptote is demonstrated and a predominantly diabatic picture of the vibrational motion emerges, indicating that the ion-pair resonances possess little state character.
[en] Highlights: • First observation of triiodide anions from ESI of iodide salt solutions. • Absence of other trihalide anions from ESI except for Br3− in low abundance. • Formation of mixed trihalide anions with iodide salt spiking. • Role of physico-chemical characteristics in triiodide anion formation. Electrospray ionization of alkali halide solutions in the negative ion mode results in the formation of cluster ions of the general formula, (MX)nX−. However, alkali iodides form triiodide anion, I3−, in high abundance in addition to cluster ions. Br3− ions are observed in low abundance. Also, mixed tri-halide anions, I2Y−, are observed in high abundance when a small amount (<1%) of KI is added to other alkali halide solutions. These results are explained by the uniquely different physical characteristics of lithium and the iodide ions compared with others in the series.
[en] Mass spectra of van der Waals or hydrogen-bonded clusters feature characteristic lower size limits for the observability of multiply charged ions. The author reviews present knowledge about the origin of this effect, including recent progress in determining decay channels of metastable, multiply charged clusters. 53 refs.; 5 figs
[en] A careful search has been made for dinegatively charged cluster ions. (O2)32- and larger homologs have been observed for the first time.They were produced via electron attachment with near zero energy electrons to neutral O2 clusters formed by nozzle expansion. (Author)
[en] To study the structural and dynamical properties of finite 3D dust clouds (Yukawa balls) new diagnostic tools have been developed. This contribution describes the progress towards 3D diagnostics for measuring the particle positions. It is shown that these diagnostics are capable of investigating the structural and dynamical properties of Yukawa balls and gaining insight into their basic construction principles
[en] Argon clusters were produced in a free supersonic molecular beam expansion of pure argon at room temperature and the photoionization efficiency curves of the trimer through hexamer were measured in the wavelength regions from threshold to 700 A. A study of the Ar+3 photoionization efficiency curve as a function of nozzle stagnation pressure shows that fragmentation of heavier clusters can dominate the spectrum, even near threshold, and even when the nozzle conditions are such that the Ar+4 intensity is only a small fraction of the Ar+3 intensity. The Ar+3 photoionization efficiency curve, obtained using nozzle stagnation conditions such that no heavier ions were detected, exhibits several broad peaks near threshold which show similarities to bands of the dimer. At high nozzle stagnation pressures, the photoionization efficiency curves for Ar+3 to Ar+6 are nearly identical due to the effects of fragmentation. These spectra exhibit two very broad features which are similar to features observed in the solid. The threshold regions for all the positive ions show extremely gradual onsets, making it difficult to determine the appearance potentials accurately. The appearance potentials for Ar+2 and Ar+3 are 855.0 +- 1.5 and 865.0 +- 1.5 A, respectively, yielding a value of 0.18 +- 0.05 eV for the dissociation energy of Ar+3. The appearance potentials for the heavier clusters Ar+4 through Ar+6 are all approximately 870 +- 2 A
[en] Highlights: • Test for heavy Rydberg behaviour in ion-pair states of H2. • Significance of the energy dependence of the quantum defect. • Difference between the ion-pair states of H2 and those of the halogens revealed by the quantum defect. Heavy Rydberg behaviour in the and ion-pair states of H2 and the state of D2, is analysed in terms of the absolute quantum defects of the vibronic levels. The influence of the inner repulsive wall of ion-pair potentials on heavy Rydberg behaviour is considered and shown to determine the size of both absolute quantum defects and their energy dependence.