Internal energy distributions deposited in doubly and singly charged tungsten hexacarbonyl ions generated by charge stripping,electron impact,and charge exchange

The distribution Pε of internal energies deposited in W(CO)₆ ^+?. ions upon charge stripping (that is, electron detachment to yield the doubly charged ion in the course of a single kiloelec-tronvolt energy collision) was estimated by a thermochemical method from the measured relative abundances of the doubly charged fragment ions produced. The thermochemical information needed to estimate P/ge was obtained by measuring the threshold translational energy losses associated with charge stripping of the singly charged fragment ions, W(CO) _n ⁺ (n = 0-5). The P(/ge) curve falls exponentially with increasing internal energy. The average energy transferred to W(CO)₆ ^+? upon a 7.8-keV collision with O₂ is 19 eV, yielding W(CO)₆ ^2? ions with an average of 4 eV of internal energy. In its general appearance, the P(ε) distribution associated with charge stripping is similar to the curves obtained from simple collisional activation of either W(CO) ₆ ^+?. or W(CO)₆ ^2+? in kiloelectronvolt energy gaseous collisions. Given that charge stripping occurs by way of an electronic excitation process, this similarity in the energy deposition function is taken to indicate that electronic excitation is also the major mechanism for simple collisional activation in this system at zero scattering angle in the kiloelectronvolt energy regime. The internal energy distribution associated with a related charge-stripping process, charge inversion from the metal carbonyl anions to yield the corresponding cations, was also recorded. This reaction shows a large (～7 eV) average internal energy deposition with a distribution that indicates near-zero probability of formation of unexcited ions. These data are tentatively interpreted in terms of vibrationalelectron detachment. The internal energy distribution associated with an exothermic process, charge exchange [W(CO)₆ ^2+? + O₂ → W(CO) ₊ ^6?+O₂ ^+?], was also characterized. Unexpectedly strong coupling of translational to internal energy is observed, and there is a large probability of depositing internal energies in excess of 10 eV, even though the exothermicity is only 3 eV. Finally, the internal energy distributions associated with the formation of doubly charged W(CO)₆ ^2+? ions by electron ionization have been measured. Unlike the distribution for charge stripping, but like that for singly charged ions generated by electron impact, this distribution shows considerable structure, presumably due to Franck-Condon factors.     

Equilibrium cation exchange on natural heulandite

Corrected selectivity coefficients are determined from the zeolite counter-ion composition and thermodynamic ion-exchange constants by studying ion-exchange equilibria in the system natural heulandite-binary aqueous solution for NaCl, KCl, CsCl, NH₄Cl, Pb(NO₃)₂, LiCl·H₂O, and Ca(NO₃)₂·4H₂O. The sorbent composition after ion exchange from multicomponent aqueous solutions of differently charged electrolytes can be calculated in advance using data for the equilibria of binary exchange.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1474–1477, July, 1990.     

Target dependence of charge exchange X-rays

This paper describes our finding that in slow collisions of Kr²⁷⁺ projectiles with neutral Ne, Ar and O₂ atoms/molecules there is a significant target dependence in the spectra of X-rays originating from electron capture. We also present results of a classical trajectory Monte-Carlo (CTMC) calculation that quantifies the different initial electronic state (n,l) distributions of the captured electrons for these three target gasses.     

Paradigms and paradoxes: fractional electron charge

Structural Chemistry - There is hardly a generic connection between the partial atomic charges, a useful concept in chemistry, and the “fractionalization” of the electron accomplished...     

Equilibrium of point defects and charge transfer in lanthanum cobaltite

The specific conductivity logσ _T and thermal electromotive force coefficient Q _T of perovskite-like lanthanum cobaltite were measured over the temperature range 1173 K ≤ T ≤ 1323 K depending on the partial pressure of oxygen (10⁻⁸ atm ≤ p _{O 2} ≤ 1 atm). The p _{O 2}-T-δ phase diagram of solid LaCoO_3-δ studied earlier was used to recalculate the electric property data into the log σ _T -δ and Q _T -δ dependences. The isoconcentration temperature dependences of specific conductivity (logσ)_δ-1/T and Seebeck coefficient Q _δ-1/T for LaCoO_3-δ were analyzed. The conclusion was drawn that charge transfer was activation in character and had a low activation energy. This was evidence that small-radius polarons (Co ^•_Co and Co ^′_Co ) were responsible for charge transfer in perovskite-like lanthanum cobaltite. The calculated equilibrium constants for the formation of electronic defects and functional dependences of defect concentration [Co ^•_Co ] _T = f ₁(δ) and [Co ^′_Co ] _T = f ₂(δ) were used to analyze polaron transfer parameters in LaCoO_3-δ.

     

Applications of charge stripping/charge exchange spectra of organic ions

The application of a new technique which involves the combination of charge stripping and charge exchange processes has been investigated. Ions are charge-stripped in the second field-free region of a triple-sector mass spectrometer (BEE geometry), and then subjected to a charge exchange reaction in the third field-free region. The resulting charge stripping/charge exchange (CS/CE) spectrum is free from interference, which is otherwise common in charge stripping spectra. Comparisons between charge stripping and CS/CE spectra are made in cases where both kinds of spectra are obtainable. In order to assess the applicability of this new technique to studies of isomeric ion structures, species for which charge stripping spectra have previously been unobtainable have been chosen. CS/CE spectra of [C₆H₆]⁺˙, [C₆H₅]⁺, [C₈H₁₀]⁺˙ and [C₇H₇O]⁺ ions from a variety of precursors are recorded: in most cases, sufficient differences are observed to permit distinction between isomeric structures (or mixtures of structures). Previous studies which have shown that stable doubly charged molecular ions of ethane cannot be formed by the charge stripping technique are confirmed from its CS/CE spectrum.     

Homogenous redox catalysis competition between electron exchange and proton exchange

Whether proton exchange and nucleophilic substitution reactions can become competitive with electron exchange reactions in homogeneous redox catalysis processes due to the reduction of bromoesters has been evaluated.Electrochemical data have been correlated with the results of the analyses carried out in solution during, and at the end of, the catalytic reduction processes. Thus, it has been possible to obtain the values of γ (γ = c_RX/c_O, where c_RX is the substrate concentration and c_O that of the catalyst corresponding to pure catalysis conditions whereby only the electron-exchange reaction is observed.The hypothesis that the catalyst (9,10-diphenylanthracene) is dihydrogenated by the substrate according to DISP₂ mechanism is in agreement with the experiments.     

Electron-electron interaction in slow charge exchange collisions

The influence of excited projectile electrons on the charge exchange mechanism is studied in slow collisions of multiply charged ions with atoms. Translational energy spectra for single electron capture are measured for projectile ions being prepared in the ground state and in an excited metastable state. The differences are discussed in terms of the electron-electron interaction, which turns out to be more important in collision systems with projectiles in low charge states.     

Equilibrium space charge distribution in a quadrupole ion trap

A simple model provides a basis for evaluating the ion spatial distribution in a uadrupole (Paul) ion trap and its effect on the total potential (trap potential plus space charge 3 acting on ions in the trap. By combining the pseudopotential approximation introduced by Dehmelt 25 years ago with the assumption of thermal equilibrium (leading to a Boltzmann ion energy distribution), the resulting ion spatial distribution (for ions of a single mass-to-charge ratio) depends only on total number of ions, trap pseudopotential, and temperature. (The equilibrium assumption is justified by the high helium bath gas pressure at which analytical quadrupole ion traps are typically operated.) The electric potential generated by the ion space charge may be generated from Poisson’s equation subject to a Boltzmann ion energy distribution. However, because the ion distribution depends in turn on the total potential, solving for the potential and the ion distribution is no longer a simple boundary condition differential equation problem; an iterative procedure is required to obtain a self-consistent result. For the particularly convenient operating condition, (a _z = -8qU/m? ₀ ² Ω², and q _z =-4qV m? ₀ ² Ω², where U and V are direct current and radiofrequency (frequency, ω) voltages applied to the trap, m/q is ion mass-to-charge ratio, and ?₀ is the radius of the ring electrode at the z=0 midplane], both the pseudopotential and the ion distribution become spherically symmetric. The resulting one-dimensional problem may be solved by a simple optimization procedure. The present model accounts qualitatively for the dependence of total potential and ion distribution on number of ions (higher ion density or lower temperature flattens the total potential and widens the spatial distribution of ions) and pseudopotential (higher pseudopotential increases ion density near the center of the trap without widening the ion spatial distribution).     

Dissociative charge exchange of C3F6

Charge exchange of neutral C₃F₆ by a variety of atomic and molecular ions in the 1 to 25 eV range of collision energies is used to characterize the energies associated with formation of [C₃F₆]⁺˙. The internal energy of the nascent [C₃F₆]⁺˙ ion, assessed by observing the degree to which it fragments, increases with the recombination energy of the charge-exchange reagent. The existence of excited states of the reagent ions is identified from the fragmentation behaviour of [C₃F₆]⁺˙ in the cases of [CS₂]⁺˙, NO⁺, O₂⁺˙, [NH₃]⁺˙ and possibly [CH₄]⁺˙. In addition, the data confirm that the [C₃F₆]⁺˙ parent ion fragments from both the ground state and a long-lived isolated electronic state. The latter is populated by near-resonant charge transfer. Translational excitation contributes relatively little to internal excitation of the charge-exchanged product ion and even less in the case of the isolated state.     

Some charge exchange reactions involving H2O

Charge exchange cross sections for the reaction of O⁺, N⁺, and N⁺₂ with H₂O have been measured over the energy range 0.2–10 eV in the center-of-mass system. The implications of these measurements for recent space experiments are discussed briefly.     

Equilibrium of Br− and Cl− exchange on strong-basic anion-exchanger

The equilibrium of Br^– and Cl^– exchange is studied on the strong-basic anionexchangers. Quantitative characteristics which can be used for elaboration of dual-temperature separation processes have been obtained. An empirical equation for the dehydration extent of an anion in a phase of a sorbent has been suggested, allowing one to calculate the Br^– and Cl^– exchange equilibrium constants on the anion-exchanger in a wide temperature range.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2083–2089, December, 1994.     

Radial exchange density and electron delocalization in molecules

The six-dimensional exchange density Gamma(X)(r1,r2) is a measure of electron delocalization at the Hartree-Fock level. Fixation of r1 to a constant point results in a three-dimensional function, which displays electron delocalization that originates from r1 in position space. In this work, the dimensionality of Gamma(X)(r1,r2) is lowered from six to four by integration with regard to r2 over sphere surfaces of radius d, centered at r1 = r. The resulting radial exchange density Gamma(X)(d,r) is visualized for constant d values as a function of r. This approach indicates regions of position space which are origins of delocalization over a certain distance d. The shape of these regions very strongly depends on d. Structures similar to pi orbital densities are observed at large d values (4.5 au) in unsaturated carbon compounds, while smaller values (1.5 au) can result in structures, which resemble the Laplacian of the electron density. The abundance of different spatial structures inherent in the radial exchange density implies interesting capabilities for the orbital-independent interpretation of electronic structures in position space.     

The role of electron exchange in cidep

An alternative vector model of chemically induced electron polarization is introduced and a scheme for exhibiting the role of exchange is described.     

Atomic radii scales and electron properties deduced from the charge density

A procedure to represent Hartree-Fock electron densities in atoms [L. Fernandez Pacios, J. Comp. Chem., 14 , 410 (1993)] defines ρ(r) as a reduced expansion of exponential functions. These analytically modeled densities (AMDs) are used in this article to develop a simple computational procedure for analyzing different atomic radii scales implemented in the commercial software system MATHEMATICA. The analysis is focused on the physical information associated to a given atomic radius as deduced from calculations depending on ρ(r). The amount of electron charge contained in the sphere of the given radius as well as the distinct contributions to the potential energy integrated up to that radius are obtained within the AMD formulation for main-group atoms H—Kr. The ASCII file needed to run the procedure within MATHEMATICA is also presented. © 1995 by John Wiley & Sons, Inc.     

Prospects for ultracold carbon via charge exchange reactions and laser cooled carbides

Strategies to produce an ultracold sample of carbon atoms are explored and assessed with the help of quantum chemistry. After a brief discussion of the experimental difficulties using conventional methods, two strategies are investigated. The first attempts to exploit charge exchange reactions between ultracold metal atoms and sympathetically cooled C(+) ions. Ab initio calculations including electron correlation have been conducted on the molecular ions [LiC](+) and [BeC](+) to determine whether alkali or alkaline earth metals are a suitable buffer gas for the formation of C atoms but strong spontaneous radiative charge exchange ensure they are not ideal. The second technique involves the stimulated production of ultracold C atoms from a gas of laser cooled carbides. Calculations on LiC suggest that the alkali carbides are not suitable but the CH radical is a possible laser cooling candidate thanks to very favourable Frank-Condon factors. A scheme based on a four pulse STIRAP excitation pathway to a Feshbach resonance is outlined for the production of atomic fragments with near zero centre of mass velocity.     

Equilibrium constants of ion exchange reactions between fatty acid monolayers and dissolved counterions

Equations for equilibrium constants of ion exchange between fatty acid monolayers and subsolution counterions are derived. The approach of Matsubara et al. [4], where the monolayer is considered as a two-dimensional regular mixture is employed, but the different molar volumes of its components are taken into account. Using the equations obtained theK _ex values are calculated on the basis of published data on the monolayer composition in the systems Cd²⁺/HArch, Ba²⁺/HArch, Ca²⁺/HSt, Pb²⁺/ HSt and Cu²⁺/HSt. The stability constants of the corresponding soaps formed in the monolayer are also obtained.     

Derivatized fullerenes bearing multiple electron donors: synthesis and charge transfer properties

A series of methano-C60 adducts bearing up to six electron donating N,N-dimethylaniline units (denoted as D compounds), along with their analogues without the dimethylamino groups as references (R compounds), were synthesized. The redox properties of the D compounds in solutions were evaluated spectroscopically in reference to the R compounds. According to UV/vis absorption results, there are obviously ground-state intramolecular charge-transfer complexes in the D series, and the charge-transfer effects apparently become saturated with only two donor units in the molecule. The photoinduced intramolecular electron-transfer properties of the D compounds were investigated via fluorescence measurements. The emission from intramolecular exciplexes can be found only in the D molecule with two electron donor units. Throughout the D series, the fluorescence properties are highly sensitive to the solvent polarity, with the emission completely quenched for all of the molecules in a polar solvent like methylene chloride. Mechanistic implications of the results are discussed.     

Nonlinear X-ray diffraction. Determination of valence electron charge distributions

A new, nonlinear X-ray diffraction technique is described which permits the direct experimental determination of the valence electron charge density in a wide variety of covalently bonded materials.