[en] Trajectory surface hopping calculations have been carried out for collision-induced dissociation (CID) collisions of H₂⁺(v) + Ar and HD⁺(v) + Ar, where the vibrational level v=0, 1, and 2, on the Kuntz-Roach diatomics-in-molecules potential surfaces up to a relative collision energy of 35 eV. The results are compared with earlier calculations for Ar⁺ + H₂(v=0) and Ar⁺ + HD(v=0). Above 10 eV CID is the major product channel. The isotope effect for H⁺ and D⁺ from HD⁺(v) and HD(v=0) strongly favors D⁺ over H⁺ at all energies. Evidence is presented that CID is a two-step process--reaction to form ArH⁺ or ArD⁺ followed by dissociation to Ar + H⁺ or Ar + D⁺ if the energy of the diatomic exceeds its dissociation energy. The modified pairwise energy model, which works well for chemical reaction, is also seen to describe the CID process well

[en] The Pairwise Energy Model (PEM) assumes that the cross section for the reaction cross section for the reaction A+BC→AB+C, where B and C are isotopes of hydrogen, depends on only the pairwise relative energy E_s between A and B. Until now, the PEM has been used to interpret theoretically the isotope effect for the reactions such as O(³P)+HD and Ar⁺(H₂, D₂, and HD). In this paper we carry out extensive quasiclassical trajectory calculations for the three possible reactions CI+H₂ and HD and show that the PEM works very well at high energy. In particular we are able to accurately predict the intramolecular isotope effect at high energy for the reaction of CI+HD using only the cross section data for CI+H₂. To understand that the PEM works so well at high energy, the internal energy distributions for the products are examined. The distributions for three reactions are different at a fixed relative collision energy E but are approximately same at a fixed pairwise energy E_s. This suggests that the PEM works very well at high energy. We believe the conclusions reached here will apply to other A+BC systems

[en] Quasiclassical trajectory calculations were carried out for the reactions of H+H₂ (v=0, j=0) and its isotope variants on the Siegbahn-Liu-Truhlar-Horowitz potential energy surface for the relative energies E between 6 and 150 kcal/mol. The goal of the work was to understand the inter^- and intramolecular isotope effects. We examine the relative motion of reactants during the collision using the method of analysis that monitors the intermolecular properties (internuclear distances, geometry of reactants. and final product). As in other works, we find that the heavier the incoming atom is, the greater the reaction cross section is at the same collision energy. Using the method of analysis we prove that the intermolecular isotope effect is contributed mainly by differences in reorientation due to the different reduced massed. We show that above E=30 kcal/mol recrossing also contributes to the intermolecular isotope effect. For the intramolecular isotope effect in the reactions of H+HD and T+HD, we reach the same conclusions as in the systems of O(³P)+HD, F+HD, and Cl+HD. That is, the intramolecular isotope effect below E=150 kcal/mol is contributed by reorientation, recrossing, and knockout type reactions

[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