[en] Classical trajectory methods have been used to explore the excitation of vibrations in gas-phase collisions of the nitrogen molecular ion with its parent molecule. The near symmetry of the reactants is shown to result in a high probability that the two molecules are excited by an equal amount of energy. This provides a possible explanation of the molecular beam measurements that show that the total number of vibrational energy quanta excited in the collision is, with a high probability, even

[en] The charge-transfer reaction of helium ions with xenon was investigated with a crossed-beam apparatus at collision energies of 5.1, 29, and 97 eV. In agreement with luminescence studies of the same reaction, the dominant product observed is the 6s ⁴P/sub 1/2/ state of Xe⁺. A deconvolution technique which removes the contribution of this near-resonant state was used to investigate the contribution of other excited states and the ground state to the observed scattering diagram. A highly structured scattering-contour diagram was revealed which allowed positive identification of several excited-state products. These states are formed directly by charge transfer rather than by cascading from higher states; they also exhibit angular-specific and quantum-state-specific scattering. A propensity rule to conserve electronic angular momentum (ΔJ = 0) is also inferred

[en] Two crossed-beam instruments with different geometry and with low pressure and differentially pumped ion sources were used to investigate collision-induced dissociation (CID) of acetone molecular ions activated by He and Ar collisions over the kinetic energy range 0.45--10 eV (center of mass). Long-lived electronically excited state(s) which back-scatter superelastically with conversion of 2.2±0.3 eV of internal energy into translational energy dominate the low collision energy (E_rel <2 eV) CID of the acetone ion. This energy release matches the X left-arrow A electronic excitation energy difference, suggesting a very efficient E→T energy transfer mechanism for this system. The location of the intensity maximum for this mechanism on the relative velocity vector (fully rebound peak) indicates that small impact parameter ''head-on'' collisions trigger this energy transfer process. A curve-crossing mechanism is suggested to rationalize these results. At collision energies of 6 eV and higher the superelastic scattering mechanism is no longer observed. Translationally endothermic forward (but nonzero angle) scattering takes over as the predominant CID mechanism. The dynamics are consistent with the hypothesis that the endothermic CID channel proceeds on the electronically excited surface and involves the efficient T→E excitation of ground state acetone ions

[en] Translational energy changes were measured in the Utah crossed-beam apparatus to explore internal energy changes in the charge transfer reaction He⁺ + Xe → He + Xe⁺. Laboratory angular and energy distributions were taken at angles from 85 to 92⁰. The energy distribution thus obtained was compared with that due to ionization of a xenon beam by electrons and it is concluded that the CT produced xenon beam has a wider energy distribution than that produced by electrons. Comparisons are made with previous measurements to suggest reaction channels and a potential energy diagram of the compound molecule existing during the collision. (G.Q.)

[en] The reaction of N₂⁺ (X,v = o) with H₂ is interesting in that the product N₂H⁺ rather than H₂⁺ appears, though the charge transfer to give H₂⁺ (X,v = o) is exoergic by 0.15 eV and a favorable Franck-Condon Factor exists for the H₂ (X,v = o) → H₂⁺ (X,v = o) transition (FCF approximately 0.087). Usually charge transfer takes over, when it competes with other reaction mechanisms. However an exception is the charge transfer between Ar⁺ and N₂, where the exoergic channel into N₂⁺ (X,v = o) does not appear at an appreciable rate at thermal and suprathermal energies. The inhibition of this exoergic transfer seems to occur due to nonexistent crossings between the Arsup+ - N₂ and N₂⁺ (X,v = o) - Ar potential curves. The same situation may in the case of the N₂⁺ (X,v = o) reaction with H₂ inhibit charge transfer, so that heavy particle transfer (hydrogen abstraction) occurs instead. For N₂⁺ (X,v = 1) however a favorable curve crossing seems to allow for a fast charge transfer. (Author)

No abstract available

[en] A new FTMS research apparatus and first results are described. Reactant ions are prepared by MALDI or Electrospray ion generation, an ion funnel for efficient ion injection, a triple quadrupole mass selector and ion collisional cooling section and an energy selector preceding ion buncher and injector lenses. A high vacuum probe lock presents an orthogonally mounted surface to the ion beam inside the solenoid field. Reflected primary ions and secondary ions are trapped in a forth-order field-corrected Penning Trap and measured by conventional FT methods. This apparatus is our newest tool for investigating mechanisms of collisional activation and dissociation of ions. In this work we compare spectra obtained with carefully controlled multiple collision SORI excitation and single collisional excitation with a perfluoroalkyl self-assembled monolayer (FSAM). Using protonated model peptides and RRKM modeling of their dissociation we deduced accurate dissociation parameters and energy transfer functions for their collisional activation. Similarities and differences in results obtained in SORI and FSAM collisional activation are rationalized in the context of recent collisional dynamics and kinetics results. (author)

[en] The crossed-beam method was used to investigate the charge-transfer reaction of Ar⁺(²P_3/2) with O₂(X³Σ_g^-, v = 0). The percentage of Ar⁺(²P_1/2) in the ion beam could be varied between about 1 and 33% by varying the operating conditions of the high-pressure ion source. Reactive scattering of Ar⁺(²P_3/2) demonstrates that several different electronic states of the O₂⁺ product are populated. Evidence that the ground-state ion appears to be highly vibrationally excited (v = 0-12) is shown. Unreactive scattering of a mixture of Ar⁺(²P_3/2) and Ar⁺(²P_1/2) at 0.85 eV shows that all accessible vibrational states of ground-state O₂ are populated as well as the fine-structure transition of Ar⁺(²P_3/2) and Ar⁺(²P_1/2). (author)