Thermal ionization

Abstract: A new method for determination of intrinsic ionization and complexation constants of oxide surface sites from potentiometric titration data is reported Using these experimental properties and the stoichiometry of surface reactions, surface charge, σo, adsorption density, Γi, and diffuse layer potentials, ψd, at the oxide/water interface are calculated The numerical method permits simultaneous calculation of all surface and solution equilibrium states in both simple and complex electrolyte/colloid systems This allows generalization to dilute ion adsorption in systems with complex solution chemistry In electrolyte solutions of moderate or high concentration, the surface charge is dominated by surface complex formation of ionizable surface sites and electrolyte ions In very dilute simple salt solutions the surface ionization reactions are more important H+ and OH− are the principal potential determining ions (pdi), but the electrolyte ions have a minor effect on the calculated surface potential, ψ0 The electrolyte ions and pdi have a joint role in determining the magnitude of the surface charge via their reactions with surface sites The important experimental parameters which characterize these contributions are ΔpKcumptex = p*Kcationint − p*Kanionint and ΔpKa = pKa2int − pKa1int

Abstract: The energy spectrum of electrons produced by multiphoton ionization of xenon atoms has been analyzed with a retarding potential technique. We have shown that the discrete absorption of photons above the six-photon ionization threshold was observable under specified conditions. A simple model based upon inverse bremsstrahlung gives a resonable agreement with the experiments.

Abstract: The site-binding model for the electrical double layer of hydrous oxides reported in a previous paper is applied to the adsorption of metal ions from dilute solution and to complex heterogeneous systems, i.e., amorphous iron oxyhydroxide. More than one stoichiometric surface reaction is usually needed to describe the adsorption behavior of dilute heavy metal ions. If mass law equations for surface reactions of metal ions are corrected for effects of the electrostatic field at the interface, the calculated adsorption density depends upon the type of surface species formed. It is shown that calculations with surface reactions involving hydrolytic complexes of metal ions, e.g., Pb(II), Cd(II), Cu(II), Ag(I), are more consistent with experimental adsorption data than complexation by bidentate surface sites. A table of intrinsic surface complexation constants for various metal ions and oxide substrates is presented. Similar to results reported earlier for major electrolyte ions, the stability constants of surface complexes of heavy metal ions with the silica surface are significantly less than for other oxide surfaces. Empirical surface parameters for model calculations with iron oxyhydroxide are derived and the results are compared with experimental adsorption data for Cu(II) and Ag(I).

Abstract: When an electron hits an atom or ion, it may knock off an electron This process is fundamental in almost all types of gas discharge The reaction is endothermic; hence there is a threshold value in the electron energy below which it does not occur In this paper, the dependence of the yield on the energy just above this threshold is derived The derivation is not rigorous because it circumvents some of the difficulties of the three-body problem by applying ergodicity, albeit in a weakened form The result is that, for atoms, the yield rises as the 1127th power of the energy excess For ions the exponent lies between this number and unity

Abstract: The origin of ions in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is currently a matter of active research A number of chemical and physical pathways have been suggested for MALDI ion formation, including gas-phase photoionization, ion–molecule reactions, disproportionation, excited-state proton transfer, energy pooling, thermal ionization, and desorption of preformed ions These pathways and others are critically reviewed, and their varying roles in the wide variety of MALDI experiments are discussed An understanding of ionization pathways should help to maximize ion yields, control analyte charge states and fragmentation, and gain access to new classes of analytes © 1999 John Wiley & Sons, Inc Mass Spec Rev 17: 337–366, 1998