Atomic Charge Transfer Research Articles

On the formation of H(n=3)dipole moments in collisions of protons on rare gas atoms

We have investigated proton-rare gas atom charge transfer collisions in the energy range from 20 to 100 keV and have extracted the electrostatic dipole moments (EDMs) of the collisionally produced H(n=3) atoms from the optical data. The results show that the EDM decreases with increasing atomic number of the rare gas atoms. Our data provide experimental evidence that post-collisional electrostatic forces do not influence the formation of the EDMs.

Effective atomic charges and charge transfer after photoionization in sulfur compounds and phosphorus compounds

The effective charges, extra-atomic relaxation energy and Madelung potentials are determined in some sulphur and phosphorus compounds using experimental values and calculations. The charge transfers after photoionization are calculated using a transition state model. The charge transfer is proportional to the polarizability of the neighbor atom for the atom under investigation. The extra-atomic relaxation energy for the 1s level is about 0.5–1.0 eV larger than that for 2p level. The effective atomic charges and Madelung potentials are in good agreement with existing theoretical calculations. The obtained data are checked by the independent determination of the effective atomic charges from Madelung potentials for AX n -type molecules.

Ultrafast experiments on intermolecular electron transfer in the benzene - bromine atom charge transfer complex

Ultrafast pump - probe measurements have been made on the benzene - bromine atom charge transfer (CT) complex in CCl 4 and cyclohexane solutions. Ultrafast optical excitation of the CT band of the complex yields an ion pair, which is comprised of a benzene cation and a bromide anion. The rate of charge recombination between the bromide and the benzene cation in the ion pair has been observed to be much faster than the rate of diffusion apart. The charge recombination rate is accelerated at high benzene concentrations as a result of the formation of a benzene dimer cation - bromide ion pair which undergoes much faster charge recombination than the benzene cation - bromide ion pair.

Natural populations and charge transfer in hydrogen and alkali bihalide ions

Equilibrium structural parameters and dissociation energies of the bihalide ions, (MXY) (M = H, Li or Na; X and Y = F or Cl) have recently been calculated [l] at ab initio HF and post-HF(MPn) levels using 6-31+G* and 6-31 l+G* basis sets. All the species were predicted to have a linear structure with a double-minima potential at R(X . . . Y) > &(X...Y). In the case of heterobihalide ions the structure (X-M . . . Y)), where X is a smaller atom than Y, corresponds to the global minimum in the potential energy surface. For the (HXY)species &(X . . . Y) is shorter than the sum of the van der Waals radii, Rx + RY. Owing to the presence of core electrons in Mf (M = Li or Na) and also its larger size, R, (X . . . Y) is longer than Rx + RY in alkali bihalide ions. These anions are binary complexes of a halide ion with hydrogen or alkali halides. Their nature of bonding was deduced by us [l] on the basis of atomic charges, charge transfer (CT) and bond indices obtained at the HF/6-31 l+G* level using the Mulliken population analysis (MPA) [2]. It was found that the CT or valence interaction plays an almost equal important role both in (HXY)and (MXY)-. This is an unacceptable result. In view of the well-known deficiency [3,4] of MPA, both atomic charges and the amount of CT are highly exaggerated especially for the alkali bihalide ions.

ChemInform Abstract: Atom Charge Transfer in Molecular Polarizabilities. Application of the Olson‐Sundberg Model to Aliphatic and Aromatic Hydrocarbons

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Atom charge transfer in molecular polarizabilities: application of the Olson-Sundberg model to aliphatic and aromatic hydrocarbons

The atom monopole-dipole interaction model of Olson and Sundberg is used to calculate molecular dipole polarizability tensors of aliphatic and aromatic hydrocarbons for light in the visible region. Atom monopole and dipole polarizabilities are optimized to fit experimental mean polarizabilities and anisotropies for seven alkanes and five planar aromatic hydrocarbons. For alkanes the best fit is obtained with vanishing atom monopole polarizabilities; i.e., for the model in which no atom charge transfer occurs. For the planar aromatic molecules the best fit is obtained by a model which includes both monopole and dipole atom polarizabilities for the horizontal (in-plane) components and only dipole polarizabilities in the vertical (out-of-plane) components

Effect of intra-atomic Coulomb repulsion on charge transfer in atom scattering on metal surfaces

Charge transfer in atom scattering on metal surfaces is usually described employing the time-dependent Anderson model. In the framework of this model, the electron hopping matrix element is assumed independent of the intra-atomic Coulomb repulsion and the occupation numbers of the adatom orbital. In the present paper, the latter assumption is relaxed. The occupation number dependence of the hopping matrix element is shown to describe the possibility of the formation of neutral, positive and negative ions in a single approach. The connection between the exact quantum mechanical result and the phenomenological master equation approach is outlined. The latter is shown to be valid for typical atom velocities, ν = 0.005−0.001 au, and is most efficient for numerical calculations. Calculated results are used to analyze experimental data for the scattering of alkali atoms on metal surfaces.

A comparative study of isoelectronic and isogyric reactions.: Part 2. Molecular orbital calculations of diatomic sulfides, oxides and halides

Enthalpies of reaction for reactions involving diatomic sulfides and oxides have been calculated at the MP n/6–31G ∗∗ ( n = 2–4) and MP4SDTQ/6–311G(2df,2pd) levels. Enthalpies of formation and singlet-triplet and doublet-quartet energy splittings have also been obtained. The species investigated include ArS + , ArO + , NeS +, NeO +, ArCl + , NeCl +, HS and HS +. The reactions investigated include proton transfer, halogen atom transfer and charge transfer. In order to facilitate the study of reaction enthalpies, the reactions have been divided into four categories: (1) isogyric and the reactant and product pairs are isoelectronic; (2) isogyric and the reactant and product pairs are valence isoelectronic; (3) isogyric; (4) not even isogyric. The results from this study are compared to those from our earlier study. It is found that the MP4SDTQ/6–311G(2df,2pd) enthalpies of reaction reproduce the experimental enthalpies within 3.5 kcal mol −1 for all but nonisogyric reactions. MP n/6–31G ∗* results reproduce the higher level computational results and the experimental results consistently well only for reactions in category (1). There is also disagreement in the energy splittings obtained with the two basis sets. Finally, some suggestions are made to experimentalists about ion-molecule reactions that may produce the above ions.

Electron transfer in nuclear reactions

The influence of nuclear reactions on atomic charge transfer in energetic ion-atom collisions is studied within a two-channel model for the reactions and the impulse approximation for electron capture. Large interference structures in the capture probability are found for the test reactions 12C(d,p)13C, 180(p,∝)15N, 19F(p,∝)160 and 32S(p,p′)32S.

Electron correlation effects on charge transfer and energy dissipation in atom or ion scattering from metal surfaces

Electron correlation effects on charge transfer and energy dissipation in atom or ion scattering from metal surfaces

Electron correlation effects on charge transfer and energy dissipation in atom or ion scattering from metal surfaces

The charge transfer and the energy dissipation in the scattering of a particle from a metal surface is investigated within the framework of the time-dependent Newns-Anderson model laying stress on the effects of the intra-atomic Coulomb interaction on the particle. The final energy distributions of the electronic system are calculated by the perturbational expansion with respect to the electron hopping matrix element between the particle and the metal surface. The numerical results up to the fourth order terms are presented for the hydrogen scattering from the tungsten surface.

Influence of nuclear reactions on electron transfer in energetic ion-atom collisions.

The influence of inelastic nuclear scattering on atomic charge transfer in asymmetric ion-atom collisions is described within a new theory, combining a two-channel model for the nuclear reaction with the impulse approximation for electron capture by the projectile. Test calculations of the capture probability during the reaction {sup 18}O({ital p},{alpha}){sup 15}N indicate that inelastic nuclear reactions are a more transparent probe for the atomic transition amplitudes than elastic resonances.

Properties and limitations of an ion guide

A flexible electrode hose of 1 m length and with a diameter of 18 mm, consisting of two helically wound wires has been built. Its ability to guide a low-energy Ar ion beam of 1 keV and 100 μA has been tested with electrode potentials up to 500 V. The Smooth Approximation of the equation of motion leads to a focussing effective boundary potential and to a critical glancing angle for ion beam reflection. Similarities with light and neutron guides are discussed. Measurements of the guided ion beam show that the beam is attenuated by atomic charge transfer along the 1 m path due to gas flow from the ion source, that beam losses occur due to fringing fields at the entrance and exit of the guide, which could be prevented in an improved version, and that the defocussing potential caused by the space charge of the low-energy heavy-ion beam diminishes the critical glancing angle severely. With thermal electrons the ion beam cannot be charge-neutralized within the two-wire structure.

Quantum‐chemical investigation on hydrogen bonding interaction of hydrogen fluoride dimer at various mutual orientations

AbstractHydrogen bonding interaction in hydrogen fluoride dimer has been investigated by quantum‐chemical calculation with 6‐311G** basis set at various mutual orientations. Atomic charges and charge transfer have been calculated by means of potential‐derived method, and decomposition of hydrogen bonding interaction has been executed. The calculation results show that there is a variation range for the energy‐stable orientations, the charge transfer in the range presents maximum value, and the charge transfer interaction plays a decisive role in the hydrogen bonding.

Multiple-scattering approach to oxygen K near-edge structures in electron-energy-loss spectroscopy of alkaline earths.

The multiple-scattering approach to the calculation of fine structure in inner-shell electron-energy-loss spectroscopy is based on a muffin-tin potential approximation. In order to extract information on atomic environment and charge transfer, it is essential to understand the relationship between the near-edge structures and the crystal potential. We compare the oxygen K near-edge structure of MgO, CaO, and SrO calculated with two commonly used ground-state muffin-tin potential models for ionic materials. Although the muffin-tin potential and the phase shifts are quite different, we found that these two models are both capable of yielding near-edge structure which is in reasonable agreement with the experimental spectra. Our results suggest that multiple-scattering calculations may not be able to differentiate between these two models for the muffin-tin potential. It appears that the near-edge structure is more affected by geometry than possible charge transfer.

Reactions of Kr+, Kr2+, Xe+ and Xe2+ ions with several molecular gases at 300 K

The reactions of the atomic ions Kr+ and Xe+ and the molecular ions Kr2+ and Xe2+ have been studied with several molecular gases at 300 K using a selected ion flow tube (SIFT). In some of the atomic ion reactions differential reactivity was observed between the spin-orbit states (2P3/2, 2P1/2) of the ions and, when this was so, the lower energy 2P 3/2 state of both ions was observed to react more rapidly than the 2P1/2 state, in accordance with the findings of previous work. Whereas charge transfer was the only reaction mechanism observed for the atomic ions, both charge transfer and inert gas/reactant molecule switching were observed in several reactions of the molecular ions, the latter process producing ions such as KrCH4+ and XeC2H2+. By considering the kinetics of the near-thermoneutral charge transfer reactions of Kr2+ with N2O and Xe2+ with COS, the dissociation energies of the molecular ions have been determined to be <or=1.15 eV for Kr2+ and <or=1.05 eV for Xe2+, both these upper-limit values being in good agreement with previous experimental and theoretical values.

The self-consistent band structure of PtS2obtained by the linear muffin-tin orbital method in the atomic sphere approximation

The self-consistent band structure and the density of states of the layer compound PtS2 have been calculated using the linear muffin-tin orbital method in the atomic sphere approximation. This calculation includes the relativistic mass-velocity and Darwin terms but excludes the spin-orbit coupling. The Barth-Hedin local exchange-correlation potential was used. The results confirm the semiconducting nature of PtS2, and the band structure obtained is in good agreement with the authors' optical experimental measurements. The results are discussed in terms of charge transfer and local coordination of the constituent atoms.

Analytic cross sections for charge transfer of hydrogen atoms and ions colliding with metal vapors

Analytic formulas are given for the total cross sections, σ, for the charge transfer in collisions of H +, H − and H with metal vapors. The cross sections considered are σ 10, σ 0−1, σ 1−1, σ 01, σ −10, and σ −11, where the subscripts represent the initial and the final charge state of the projectile. The functional form of the formulas is a modification of the semiempirical formula proposed by Green and McNeal for σ 10 of H + in gaseous atoms and molecules. Values of adjustable parameters in the formulas have been determined by least-squares fits to a compiled set of experimental data. The root-mean-square deviation of the data from the formula is from 7 to 34% for each type of cross section. The main cause of larger deviations is the discrepancy among the data.

Applications of accelerator-based low-energy positron beams in atomic physics

Applications of LINAC-based positron beams in atomic physics are described. The following broad subject areas are treated; e+ mobility and momentum transfer cross section determinations, angularly resolved and integral cross sections for e+-atomic processes plus charge transfer (Ps formation) type experiments, experiments with tunable positronium beams and experiments with thermal Ps sources. In addition, some discussion is given concerning the use of channel electron multiplier arrays (CEMAs) in conjunction with charge coupled devices (CCDs) as position sensitive detectors.

The classical theory of charge transfer and ionisation processes in collisions between complex atomic ions

The classical theory of charge transfer and ionisation of hydrogen atoms by protons, first developed by Abrines and Percival (1966), is extended to the case in which the interactions between the three particles are not of pure Coulomb type. The model adopted is one in which only the active electron is treated explicitly; the two residual atomic ions are considered to be simply polarisable cores. The two-body interactions are represented by semiempirical central potentials and additional three-body terms are included in order to allow fully for polarisation.