[en] Short communication

[en] Short communication

[en] The formation of fragment ions from C₆₀ due to electron impact ionization leading to a bimodal fragmentation pattern with a minimum around the cluster size of 30 is investigated with help of mass spectrometric techniques. Based on a detailed analysis of the energetics and kinetics of the singly- and multiply-charged fragment ions by two-sector field mass spectrometry (MIKE-scans) we can conclude that on the one hand some of the dissociation reactions proceed via evaporation of an intact C⁺₆ or C⁺₄ unit. (and not via the sequential loss of smaller molecular carbon units). On the other hand, measured appearance energies and the direct observation of sequential C₂-loss reactions confirm that the sequential loss of neutral C₂ units is the dominant production mechanism for C^z+_n fragment ions with sizes 40 < n < 60. (orig.)

[en] We have used mass spectrometric techniques to determine the appearance energies for the formation of small, singly charged C_n⁺ fragment ions (3 <= n <= 10) produced by controlled electron impact on C₆₀ under single collision conditions. The measured appearance energies range from 79 eV (C₃⁺) to 91 eV (C₁₀⁺) and show, within the experimental error bar of ± 5 eV, little variation with the cluster size. This result is distinctly different from the behaviour of the previously measured appearance energies for the large fragment ions C₅₈⁺ to C₄₄⁺ and indicates that the small fragment ions are the result of a different fragmentation pathway. (author)

No abstract available

No abstract available

[en] Electron ionization cross-sections for CO, CO dimers and trimers have been investigated near the threshold with a newly constructed crossed beams apparatus using a hemispherical electron monochromator (HEM) to monochromatize the primary electron beam. The dissociative attachment cross-section curve for CO used to test the new set-up shows, in accordance with the high-resolution study of Stamatovic and Schulz, a vertical onset at the thermochemical threshold (9.63 eV) of the lowest possible DA channel O^-(²P)+C(³P) in excellent agreement with the value of 9.63 eV derived from known thermochemical data, thereby indicating an energy scale accuracy of better than 10 meV. The appearance energies (AE) of some rare gases (Ar, Kr, Xe) and molecules (N₂, O₂, N₂O) measured for calibration purposes agreed with the known ionization energies (IE) of these compounds within 10 meV. Using a novel data handling procedure, involving a simultaneous non-linear weighted least-squares fit of two functions, the following appearance energies were obtained from the measured ionization cross-section curves using the AE(CO⁺) as reference: AE((CO)₂⁺)=13.19±0.10 eV and AE((CO)₃⁺)=12.98±0.34 eV. These values are in fair agreement with ionization energies values obtained in a high-resolution photoionization experiment by Ng and co-workers yielding 13.05±0.04 and 12.91±0.04 eV, respectively. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

No abstract available

[en] Using a two sector field mass spectrometer in combination with a crossed beams ion source we have obtained direct experimental evidence that C₆₀ fragment ions such as C₅₈,C₅₆,C₅₄,...produced by electron impact ionization of C₆₀ may be formed by unimolecular decay of the C₆₀ parent ion involving sequential loss of C₂. Moreover, by comparing experimental and theoretical breakdown graphs the overriding conclusion is that in the case of C₅₆^z+ production (with z=1,2,3) sequential loss of two C₂ units dominates over the loss of a single C₄ unit. copyright 1996 The American Physical Society

[en] This book contains the abstracts of the papers presented at the III Meeting of the Structure and Reactivity of Molecular Ions-SRMI European Network. Content: 1 - Invited talks: - Non adiabatic ion-atom collisions by crossed molecular beams; - Competitive isomerization and dissociation of energy selected organic ions; - Charge transfer effects on the range, strength, and anisotropy of interatomic forces; - A trajectory study of the reaction O^- + HF → OH + F^-; - Calculations on reaction dynamics of ions; - Mid-infrared spectra of ionic proton-bound complexes: intramolecular interactions and solvation effects; - A product-state resolved study of the reaction of O^- with D₂ and H₂; - Differential cross sections, measured with Guided-Ion-Beams; - Vector correlation analysis for electron-ion coincidences experiments. Photoionization of O₂ in the 20-25 eV region; - Dissociation of COS⁺ ion by photoionisation - Experiments and ab-initio calculations; - State-selected ion-molecule reactions at low collision energies; - Calculation of resonances in molecular complexes; - Ion-molecule reactions: Applications for on-line monitoring of volatile organic compounds at ppb concentrations; - CRESU studies of electron attachment at low temperatures; - Spectroscopy and astrophysics of molecular ions; - Reactions of H₃O⁺.(H₂O)_0,1,2,3, NO⁺ and O₂⁺ with some organic molecules. 2 - Poster session: - Toward ultrahigh mass resolution detection of 25 atmospheric trace gases: a preliminary study using the Orsay Tricyclotron; - Investigation of volatile organic compounds in urban air by proton-transfer mass spectrometry (PTR-MS); - Chemical reaction of dications: a beam scattering study of CF₂D⁺ and CF₂⁺ formation in CF₂⁺⁺ D₂ collisions; - Reactions in collisions of fine structure state selected argon ions with H₂, and Krypton ions with CH₄, measured with a new PEPICO apparatus; - Charge-transfer reactions between fast neutral ions and stored ions in the new TITAP apparatus; - Rotational relaxation of N₂⁺(X²Σ_g, v = 0, J) probed by laser-induced charge transfer with Ar; - Charge transfer of krypton ions with methane molecules from thermal energy to 10 eV; - Crossed molecular beam study of chemiluminescent inelastic collisions in the Rb-Rb* system; - Association versus charge transfer in the reaction of O₂⁺ and Xe⁺ with acetonitrile; - Semiclassical coupled wave packet treatment of the reaction H₂⁺(v) + Ar → ArH⁺ + H; - Pairwise energy model applied to exothermic ion-molecule reactions; - A combined experimental and theoretical study of the charge exchange-excitation reaction: He⁺ + H₂ → HeH⁺ + H*; - Effect of translation-to-vibration resonances on low energy H⁺ + O₂(X ³Σ_g^*, v = 0) → H⁺ + O₂⁺(2 Π_g, v'') charge transfer cross section; - Energy dependence of the isomerization of HCN⁺ to CNH⁺ via ion molecule reactions; - Thermodynamic data on the HCN/HCN⁺ system; - Alignment and orientation of auto-ionized oxygen atoms produced by O₂ photodissociation; - Molecule frame photoelectron angular distribution in oriented CF₃X (X= Cl, Br) using the ARPEPICOI technique; - Spectroscopy and reactivity of ionic benzene-water clusters; - Stability and reactivity of water cluster ions; - Existence of two internal energy distributions in jet formed heteroclusters: examples of the anthracene-argon system (n≤6); - Configuration dependence of electron transfer in jet cooled van der Waals complexes: experiment and modelling; - Dissociative recombination of rare gas hydrides; - Photoionization and EELS studies of fluoranthene and fullerenes; - Cheap and correct potential surfaces for ionic clusters; - Accurate ab initio calculations of potential energy curves and transition dipole moments of the Ar₂⁺ system; - High resolution infrared absorption spectrum of N₄⁺; - Surface induced dissociation of molecular and cluster ions; - Electron impact ionization and attachment under high energy resolution; - Radiation emission from the ion-ion recombination reaction of NO⁺ with Cl^- and I^-; - Dissociative ionization of methyl chloride and methyl bromide by collision with metastable neon atoms; - A quasi-classical and approximate quantum mechanical study of the isotope effect in proton transfer elementary reactions: the Ne + HD⁺ → NeH⁺ (NeD⁺) + D(H) system