Diabatic potential energy surfaces of H+ + CO

Ab initio adiabatic and diabatic surfaces of the ground and the first excited electronic states have been computed for the H⁺ + CO system for the collinear (γ = 0°) and the perpendicular (γ = 90°) geometries employing the multi-reference configuration interaction method and Dunning’s cc-pVTZ basis set. Other properties such as mixing angle before coupling potential and before coupling matrix elements have also been obtained in order to provide an understanding of the coupling dynamics of inelastic and charge transfer process.     

Trajectory surface-hopping study of the K + O2 collision: Energy transfer in neutral and ionic products

The K + O₂ collision has been studied at low energy by three-dimensional trajectory surface-hopping calculations. The diabatic potential energy surfaces used to describe the electronic states involved in the collision have been built using an analytical semi-empirical model and have not been fitted to experimental results. The double-peak structure experimentally observed in the energy-loss spectrum for K⁺ production is confirmed; but it appears that the high-energy-loss peak is due to efficient T-V energy transfer and not to electronic excitation of the O₂^? molecular ion. The energy transfer mechanism is explained by a comparison between the vibrational period of the target and the collision time which depends upon the collision energy.     

New ab initio Potential Energy Surfaces for Cl（^2P3/2,^2P1/2）＋H2 Reaction

New global three dimensional potential energy surfaces for the Cl＋H2 reactive system have been constructed using accurate multireference configuration interaction calculations with a large basis set. The three lowest adiabatic potential energy surfaces correlating asymptotically with Cl（^2p）＋H2 have been transformed to adiabatic representation, which leads to a fourth coupling potential for non-linear geometries. In addition, the spin-orbit coupling surfaces have also been computed using the Breit-Pauli Hamiltonian. Properties of the new potential are described. Reaction dynamics based on the new potential agrees with the recent experimental results quite well.     

Excited states of gaseous ions. V. The predissociation of the h2o+ ion

The B?² state of H₂O⁺ is predissociated twice. First, by the ã⁴B₁ state, giving OH⁺ + H fragments via spinorbit coupling interaction. Secondly, by a²A state, giving H ⁺ OH fragments via spin-orbit coupling and Coriolis interactions. A vibrational analysis of the photoelectron band of the B? state of H₂O⁺ and D₂O⁺ is carried out. This provides the vibrational frequencies of the H₂O⁺, D₂O⁺ and HDO⁺ ions, as well as a vibrational assignment of the peaks. The H₂O⁺ ion in its B?²B₂ state is found to have a OH bond length of 1.12 A and a valence angie of 78°.In order to describe the unimolecular fragmentation process, a distinction is introduced between the totally symmetric, optically active vibrational modes, and the antisymmetric ones which are coupled to the continuum. The former are supplied with photon or electron impact energy, but only the latter are chemically efficient. The dynamics of the dissociation process depends therefore on the couplings among normal modes. This is studied in the framework of two models. In Model 1, it is assumed that, as a result of the anharmonicity of the potential energy surface, only even overtones of the antisymmetric vibration are excited by Fermi resonance. In Model II, excitation of the odd overtones is provided by vibronic coupling. Model II is in better agreement with experiment than Model I. Calculated and experimental results have been compared on the following points: isotopic shift on the appearance potential of OH⁺ and OD⁺ ions, shapes of the photoionization curves, fragmentation pattern with 21 eV photons, presence of a unimolecular metastable transition, production of O⁺ ions. All the vibrational levels situated above the dissociation asymptote are totally predissociated. Autoionization is shown in this case to contribute only to the formation of molecular H₂O⁺ ions, and not to that of the OH⁺ fragments. For 21 eV electrons, the contribution due to direct ionization is calculated to represent about 25% of the total cross section, the rest being due to autoionization.     

Time-dependent close coupling for vibrational excitation in three dimensions: Application to H+ - H2

Impact parameter calculations for the non-reactive H⁺ + H₂ (n_i = 0) → H⁺ + H₂ (n_f) collision are reported for energies 10 eV ? E_cm ? 200 eV describing the rotational motion of the molecule in the sudden limit. The time-dependent Schrödinger equation for the vibrational motion has been solved by close coupling techniques expanding the vibrational wavefunction into both harmonic and numerically exact H₂ bound states. The convergence in vibrational basis sets, where up to six vibrational levels are considered, becomes worse with decreasing energy and increasing inelasticity. Furthermore, the harmonic wavefunctions are not suitable over a large range of energies to calculate proper cross sections. The various integral and differential cross sections have been compared with the classical results of Giese and Gentry.     

Thermal-energy charge transfer of Ar+ with H2O: Internal and kinetic energy of the product H2O+

The reaction of Ar⁺ with H₂O has been investigated at near-thermal energy. The product ions H₂O⁺ and ArH⁺ account for 90 and 10% of the total reaction rate, respectively. Kinetic energy measurements and emission spectroscopy of the H₂O⁺ product ions are reported. It is concluded that at least 60% of H₂O⁺ ions are in the X? state with ≈2.4 eV vibrational energy while up to 40% are in the à state with a mean vibrational energy of 1.4 eV; the à state vibrational distribution has been determined. It is shown that both H₂O⁺ states are populated via an energetically “non-resonant” charge transfer process.     

He++N2 Charge Transfer Reaction: An Ab initio Analysis

An ab initio analysis on the involved potential energy surfaces is presented for the investigation of the charge transfer mechanism for the He⁺+N₂ system. At high collision energy, as many as seven low-lying electronic states are observed to be involved in the charge transfer mechanism. Potential energy surfaces for these low-lying electronic states have been computed in the Jacobi scattering coordinates, applying multireference configuration interaction level of theory and aug-cc-pVQZ basis sets. Asymptotes for the ground and various excited states are assigned to mark the entrance (He⁺+N₂) and charge transfer channels (He+N₂⁺). Nonadiabatic coupling matrix elements and quasi-diabatic potential energy surfaces have been computed for all seven states to rationalize the available experimental data on the charge transfer processes and to facilitate dynamics studies.     

Stability constants of the Li+, Na+, H3O+, NH4+, Ag+, and K+ complexes of the cone conformer of tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate in nitrobenzene saturated with water

Abstract  

From extraction experiments in the two-phase water–nitrobenzene system and γ-activity measurements, the stability constants of the tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate (cone)·M⁺ complexes (M⁺ = Li⁺, H₃O⁺, NH₄ ⁺, Ag⁺, or K⁺) were determined in water-saturated nitrobenzene. It was found that these constants increase in the cation order NH₄ ⁺ < K⁺ < H₃O⁺ < Ag⁺ < Li⁺ < Na⁺.     

Solvent extraction of H3O+, NH4+, Ag+, K+, Rb+ and Tl+ into nitrobenzene by using cesium dicarbollylcobaltate in the presence of a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constants corresponding to the general equilibrium M⁺(aq) + 1·Cs⁺(nb) \rightleftarrows \rightleftarrows 1·M⁺(nb) + Cs⁺(aq) taking part in the two-phase water–nitrobenzene system (1 = hexaarylbenzene-based receptor; M⁺ = H₃O⁺, NH₄ ⁺, Ag⁺, K⁺, Rb⁺, Tl⁺; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the ML⁺ complex species in nitrobenzene saturated with water were calculated; they were found to increase in the series of Rb⁺ < K⁺ < Ag⁺, Tl⁺ < H₃O⁺, NH₄ ⁺.     

Charge transfer mechanism in N4+ + He and B3+ + He/H2 ion–atom/molecule collisions

Ab initio potential energy curves and coupling matrix elements of the molecular states involved in the collision of the N⁴⁺(2s)²S and B³⁺(1s²)¹S multicharged ions on the helium atom or molecular hydrogen have been determined by means of configuration interaction methods. The total and partial electron capture cross-sections have been evaluated in the frame of a semiclassic approach in the 1- to 100-keV laboratory energy range and compared to experimental data. A comparative study of both targets is performed in the case of the B³⁺ ion. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Neutral scattering and vibrational excitation in K+Br2 Collisions

Differential cross sections are presented for neutral scattering of K atoms in collisions with Br₂ molecules in the energy range from 20 to 150 eV. In addition energy-loss spectra for the scattered K atoms are shown. The differential cross sections show a large peak near the forward direction. The energy-loss spectra point to considerable vibrational excitation at small angles. The results are attributed to reneutralization from an ion-pair state formed during the collision. In some cases this process can involve three potential surface crossings. The experimental results can be reproduced in simple trajectory calculations on diabatic potential surfaces. The calculations show that the forward scattering is rainbow scattering, caused by the internal motion of the Br₂^? molecular ion during the collision. There is no analog to this rainbow in atom-atom scattering. The internal moti is also responsible for the observed vibrational excitation.     

Vibrational effects in proton and charge transfer in the H+2 + Ar system

Reaction and charge transfer of H⁺₂ + Ar to give ArH⁺ and Ar⁺ have been investigated as a function of H⁺₂ vibrational quantum state and kinetic energy (Ec.m.), using photoionization and guided beam ion optics. Resonance effects are important in charge transfer; proton and charge transfer are closely coupled for Ec.m. 3 eV.     

Collisional Dissociation of CH3O2+

The collision-induced breakup of CH₃O₂⁺ ions, produced in various binary ion—neutral reactions, was investigated in a drift experiment in the energy range from 0.2 to 1.2 eV. The products observed were HCO⁺ (50%) and H₃O⁺ (50%), independent of the collision energy inducing the breakup. The energy barrier for the breakup is 22 ± 6 kcal/mole.     

Solution raman spectra and normal coordinate analysis of the H3CPH+3 and H3CPD+3 cations

The Raman spectra of solutions of H₃ CPH₃⁺ and H₃ CPD₃⁺ in aqueous concentrated hydrochloric and deuterochloric acid are reported together with polarisation data. A complete vibrational assignment is given on the basis of C_3v, symmetry except for the inactive A₂ mode. A set of valence force constants and potential energy distributions have been calculated from the data of the two isotopes H₃ CPH₃ and H₃⁺ CPD⁺₃. For H₃ CPD⁺₃ the potential energy distribution demonstrates strong interaction between the P-C stretching and the symmetrical PD₃ deformation mode.     

Mobilities of H+3 and HeH+ ions in helium gas and rate coefficient for HeH+ + H2 → H+3 + He

The mobilities of mass-identified H⁺₃ and HeH⁺ ions in helium and the reaction rate coefficient for HeH⁺ + H₂ → H⁺₃ + He have been measured by a drift-tube quadrupole mass spectrometer at 300 K. The zero-field reduced mobilities of H⁺₃ and HeH⁺ ions, corrected to 273 K, are 31.0 ± 0.8 and 23.4 ± 0.6 cm² V^?1 s^?1 respectively. The reaction rate coefficient was found to be (1.26 + 0.16) × 10^?9 cm³s^?1 and was observed to be independent of the mean ion kinetic energy in the range from 0.04 to 0.3 eV.     

Measurements of differential cross sections for vibrational quantum transitions in scattering of Li+ on H2

A pulsed monoenergetic ⁷Li⁺ ion beam (lab. energy 10–40 eV) is scattered from a highly collimated (= 1.5°) H₂ nozzle beam. The time-of-flight spectrum of the ions scattered in the forward laboratory direction shows both a fast peak corresponding to forward center-of-mass scattering and a slow peak corresponding to wide-angle center-of-mass scattering. These peaks have been further resolved to show contributions from individual vibrational quantum transitions. From an analysis of the time-of flight spectra the differential inelastic cross sections for a wide range of angles and energies between 2 eV <E_cm < 9 eV have been determined. The spectra also contain information on rotational inelastic cross sections.     

Theoretical investigation of the Na+ + H2 system. III. Trajectory calculations of vibrationally inelastic collision processes

On the basis of an analytical potential energy surface for the electronic ground state of the Na⁺ + H₂ system reported recently, extensive trajectory calculations have been performed to study the collision dynamics of vibrationally inelastic processes at total energies up to ～3 eV. Special attention is given to the relative efficiacy of translational and rotational energy, respectively, in promoting vibrational energy transfer. Vibrational transitions are found to be substantially enhanced by initial molecular rotation. Furthermore, the applicability of simple models is discussed.     

Lifetimes of N2O+(Ã2Σ+) and COS+(Ã2Π) in selected vibronic levels

Lifetimes of selected vibrational levels of the predissociated òΣ⁺ and Ã²Π electronic states of N₂O⁺ and COS⁺, re- spectively, have been measured. These values have been used in conjunction with previous data on fluorescence quantum yields to obtain predissociation rates for the various vibrational levels.     

A State-selected study of the symmetric charge transfer reaction H2+ + H2

We have measured the relative total charge transfer cross sections of H₂⁺ + H₂ as a function of the vibrational state of H₂⁺, υ′_o = 0–4. using the crossed ion-neutral beam and high-resolution photoionization methods. The experimental results obtained at a center-of-mass collisional energy of 22.5 eV are found to be in excellent agreement with a recent theoretical study.     

Dynamics of the reaction H2+(He,H)HeH+. Influence of various forms of reactant energy on the total and differential cross section

Results of quasiclassical trajectory calculations of reactive processes between He atoms and H₂⁺ (υ, J) molecular ions in the collision energy interval 0.5–5.0 eV (c.m.) for a large number of selected υ, J combinations are analyzed with respect to the influence of the initial translational, vibrational, and rotational energy on the total and differential reaction cross sections. Vibrational energy is more effective in promoting the reaction than translational energy. Small rotational excitation has a negligible effect, whereas high rotational excitation has a similar influence on the reaction cross sections as the vibrational excitation of the same magnitude.