Electron Transfer Cross Sections Research Articles

Stopping cross sections forN4+→Hat low projectile velocity

We study the time-dependent dynamics of N 4 + ions colliding with atomic hydrogen for projectile energies ranging from a fraction of an eV/amu up to 25 keV/amu using the electron-nuclear dynamics (END) formalism. The END theory obtains the electron-nuclear coupled equations of motion from the time-dependent variational principle employing a coherent state parametrization of the wave function. This approach leads to a simultaneous nonadiabatic dynamics of all the electrons and nuclei. We calculate and discuss dynamical trajectories, deflection functions, final charge states, differential cross sections, and energy loss. Quantum effects of the forward peak scattering are emphasized. Due to the strong interaction between the heavy and the hydrogen atom, a diffuse ion (vide infra) is formed, leading to acceleration or energy gain of the projectile. For the case of the electron transfer cross section, we found that it does not follow the Langevin-type cross section at low projectile energies as reported by other methods. Present results show good agreement with available experimental data.

Extended description for electron capture in ion-atom collisions: Application of model potentials within the framework of the continuum-distorted-wave theory

We perform an extension of the continuum-distorted-wave (CDW) approximation for single electron capture by introducing model potentials to describe the interaction of the active electron with the residual-target and projectile ions. The cross sections for electron transfer in collisions of bare and dressed projectile ions with H and He atoms are calculated and compared with experimental data and previous CDW calculations that make use of approximate analytical wave functions to represent the active electron initial and final states. For electron capture in proton-He collisions into definite final states the present calculations are in better agreement with experiments. We trace the differences in the results from both models to a different behavior at projectile scattering angles close to the Thomas peak. In the case of dressed projectiles with different charge states impinging on H and He the present version of CDW gives a better representation of the filling of the unoccupied orbitals of the dressed ion and, therefore, of the cross section as a function of the impinging ion charge state.

Charge Transfer of O5+and O4+with CO at keV Energies

Charge transfer emission has been reported to be the dominant source of X-rays in cometary atmospheres. The emission model is based on the estimated charge transfer cross sections of solar wind minor/heavy ions and cometary neutrals. We report the results of our measurements on the absolute total one and multielectron transfer cross sections for Oq+ (q = 5, 4) with CO at ~1.5q keV energies using a technique that combines a laser ablation ion source and a reflection time-of-flight mass spectrometer. The total single electron transfer cross sections for O5+ and O4+ ions with CO are 3.42(±0.50) × 10-15 and 2.91(±0.41) × 10-15 cm2, respectively. The cross sections for multielectron transfer are 1.15(±0.37) × 10-15 and 1.03(±0.28) × 10-15 cm2, respectively.

Subshell Differential Cross Sections for Electron Transfer in Collisions of U90+ Ions with Gaseous Targets

Balmer spectra produced in collisions between He-like uranium projectiles and gaseous targets (N2, Ar, Kr, and Xe) were measured at the jet-target area of the ESR storage ring. The X-ray radiation were recorded in coincidence with the down charged projectiles having captured one electron from the target atom. By means of spectra simulation, all the significant Balmer transition lines were identified. Further, the j-differential cross sections for electron capture into projectile subshells were deduced from the well resolved spectra. For the heavier targets, where NRC contributes considerably, systematic deviations between experiment and the continuum distorted wave approximation are observed

Strong double K-K transfer channel in near symmetric collision of Si+Ar at intermediate velocity range

We present a combined study of single and double K-K electron transfer cross sections along with the single and double K-shell ionization of Ar induced by Si projectiles in the energy range 0.9-4.0 MeV u-1. The charge-state dependence of the normal and hypersatellite x-rays was used to derive the cross sections for the one- and two-electron processes, respectively. The enhancement in the fluorescence yields due to multiple vacancies was measured from the energy shifts and intensity ratios of the characteristic x-ray lines to derive K-shell vacancy production cross sections from x-ray production cross sections. The ratio of double to single K-K transfer cross sections is found to be quite large for this nearly symmetric collision system, whereas the ratio of double to single ionization cross sections is quite small. The measured single K-K transfer cross sections are reproduced very well by the two-centre close-coupling calculations whereas the double K-K transfer data are underestimated by the theory based on the independent-electron approximation (IEA). The K-shell ionization cross sections are found to deviate strongly from the calculations based on the continuum distorted wave eikonal initial state (CDW-EIS) and ECPSSR models. The CDW-EIS calculations along with the IEA model grossly underestimate the double ionization cross sections. It is stressed that in the case of two-electron processes the independent-electron model breaks down and the possible role of correlations between K-electrons is discussed.

Subshell Resolved L-K Electron Transfer and Ionization of Yb with Si Ion Impact

We have measured subshell resolved L-K electron transfer cross sections from the L subshell of the Yb target to the vacant K-shell of the Si projectile at energies varying between 2–4.5 MeV/A. In addition, the L subshell ionization cross sections are also obtained for Yb. It is observed that contrary to expectations, the L2 subshell electron transfer as well as ionization cross sections are substantially lower than the corresponding cross sections for the L1 subshell.

Ab initio calculation of the asymmetric electron transfer cross section in the low velocity collision

The one-electron molecule has been studied and the electronic energies of the states n = 1-5 have been determined as a function of the distance R between the two nuclei, in the Born-Oppenheimer approximation. The radial and rotational matrix elements for electron transfer in the collision have been computed and the system of 35 coupled equations describing the collision in the impact parameter approximation has been solved for an initial system composed of an incident ion and a target in the ground state. The signs of the different terms appearing in the radial matrix elements have been carefully re-examined and a clear resonance induced by the avoided crossing of the and states has been proven. The total electron transfer cross section is found to lie between those of the adjacent symmetric systems and and, in this respect, may be called `quasisymmetric transfer'.

Effects of excitation and orbital alignment on electron transfer in -Na collisions

The effects of excitation and orbital alignment on the electron transfer process in - collisions are investigated experimentally and theoretically over a wide range of impact energies. Experimentally, the integral alignment parameter and the ratios between the integral transfer cross sections for targets to that for a target have been determined using an optically prepared target. The results are in good agreement with earlier data at lower energies of Campbell et al. Theoretically, the integral cross section results of our 26-state two-centre atomic orbital close-coupling calculations are in good agreement with all experimental data, including the absolute electron transfer cross section measurements of Daley and Perel. These processes are now well understood over more than three orders of magnitude for the impact energy range.

Electron-Transfer Dynamics at GaAs Surface Quantum Wells

Interfacial electron-transfer dynamics have been characterized for a heterogeneous semiconductor−liquid junction. Molecular beam epitaxy was used to grow As-capped GaAs (100) surface quantum wells. Removal of the As layer created a pristine, low defect, surface which was studied in situ in direct contact with an outer-sphere, ferrocene, redox couple using time-correlated single photon counting. The surface quantum well structure was used specifically to remove field-dependent transport effects from the photocarrier dynamics. Concentration-dependent decay profiles indicate that a significant fraction of electrons undergo electron transfer. A fit to the data gives an electron-transfer cross section of (2.4 ± 0.8) × 10-15 cm2, which corresponds to charge transfer in the adiabatic coupling regime. This work illustrates that the electronic coupling between the solid state and molecular states at the surface can be sufficiently strong to produce adiabatic reaction conditions even for weakly physisorbed outer-sp...

Polarization of Li(2p) produced by -Na(3s) collisions

The differential cross sections for electron transfer in -Na(3s) collisions in the 0.4-14 keV energy range are studied using the impact parameter semiclassical method and a 28-state molecular orbital basis model including a common translational factor. The calculated differential cross section (DCS) for electron transfer to Li(2s) and Li(2p) and the three Stokes parameters of the Li(2p) final state are in excellent agreement with the measured DCS at 1 keV and 3 keV. The energy dependence of the final-state polarization for electron transfer to Li(2p) is explained using animations of the density and current of the electronic wave function complemented by time-dependent molecular state populations. We find that different transfer mechanisms dominate at low and high collision velocities.

Electron nuclear dynamics of charge-transfer collisions of protons with atomic oxygen

The electron nuclear dynamics theory is applied to the study of proton collisions with ground-state oxygen atoms at collision energies of 0.5, 1.0, and 1.5 keV. Total electron transfer cross sections are calculated in reasonable agreement with recent expe

Angular Differential Cross-Section for Electron Transfer in ION-ION Collision

Angular differential cross-sections for the formation of He 0 in collision between fast He+ ions are calculated using distorted wave Coulomb—Born approximation. The interaction potentials satisfy necessary Coulomb bound- ary conditions. In absence of any other theoretical results the present results are compared with the existing experimental data.

State-to-state cross sections in collisions

In continuation of recently published total capture cross sections for electron transfer from Na(3s) and Na(3p) initial states, we report detailed partial cross sections from coupled-channel calculations using a one-electron model for the collision system. Results are presented for Na(3p) excitation and for capture into various subshells of He where some experimental results are available. We shall focus, in particular, on state-to-state integral cross sections for electron transfer from aligned or oriented Na(3p) states into aligned and oriented states where experimental results may become available. We predict significant alignment and orientation anisotropies in the energy range in singlet as well as triplet channels. We show that previous deviations between experiment and theory in estimating the alignment anisotropy parameter for total capture may be related to the omission of the states in the capture channels.

Extension of classical trajectory Monte Carlo calculations to ion–Rydberg-atom collisionsin a magnetic field

Theoretical electron transfer cross sections for 1.3--130 eV/amu singly charged ions colliding with Rydberg atoms (n=28, m=2) in a magnetic field up to 4 T are presented. Both paramagnetic and diamagnetic interactions are taken into account for the initial state and the collision. Cross sections are calculated within the classical trajectory Monte Carlo model. A method to create a classical ensemble of electrons in a nonseparable Hamiltonian allows the initial quantum stationary states to be modeled. The effect of the magnetic field on electron capture is analyzed in terms of the field-induced alteration of the initial state, as well as the direct influence on the collision dynamics.

Photogenerated hot electron dynamics at GaAs (100) surfaces

MBE grown GaAs (100) surface quantum wells were studied using time-resolved two-photon photoemission spectroscopy where the electron distribution was directly determined. Relaxation lifetimes from 50 to 450 fs were measured and were found to be dependent on the energy of the excited electron distribution. Radiative lifetimes at the semiconductor - liquid interface were obtained using time-correlated single-photon counting. From the concentration dependence and other studies, we estimate that the electron transfer cross section is comparable to the molecular cross sections, i.e. electron transfer approaches the adiabatic limit and conditions are optimal for hot electron capture. This work provides parameters to make the hot electron transfer channel competitive with electron relaxation enabling a future generation of solar cells exploiting hot electrons.

A scaling law for charge transfer cross-sections

Based upon the extended classical over-barrier model, a simple scaling relation has been proposed for electron transfer cross-sections of collisions between low energy, highly charged ions and neutral particles. It is shown that the presently available experimental cross-sections are reproduced well with this scaling law.

Convergent TCAO close-coupling calculations for electron transfer, excitation and ionization in intermediate keV collisions

Our recently developed two-centre atomic orbital (TCAO) close-coupling method is applied to - H(1s) collisions in the impact energy range from . Convergent cross sections are obtained for this system by using a large number of bound and pseudostate basis functions on the target and a limited number of bound states on the projectile. Cross sections for electron transfer to 1s, , , and , for excitation to , , and and for ionization are presented and compared with available experimental data and other theoretical calculations. The accuracy of the previous TCAO close-coupling calculations is challenged and the reliability of some experimental data for this system is questioned.

Electron transfer into high-n states of Be3+ in slow Be4+-He collisions

We study electron transfer in Be4+-He collisions at 2-150keV/u. The system is described in the semiclassical close-coupling formalism. By considering only one active electron, cross sections for electron transfer could be determined for final states ranging up to the Be3+ n = 9 states. We study also transitions from an initially excited He 2 1S state.

Angular Differential Cross-Sections for Electron Transfer in Collisions between Proton and He+(1s) Ions

Angular differential cross-sections for the formation of H, as a result of electron capture by proton from He+ (1s) at the centre-of-mass energies from 4 to 24 keV, are calculated using distorted wave Coulomb-Born approximation. The total interaction potentials in the prior-interaction channel and in the post-interaction channel are considered. Coulomb boundary conditions are taken care of with the proper choice of the perturbation potentials in both the prior and the post channels. A prior-post discrepancy is noted. Existing theoretical results are presented along with the present results.

Alignment effects in electron transfer: Experimental studies for singly charged ion collisions with Na(3p) atoms

This paper reports experimental results for the influence of target excitation and orbital alignment on the electron-transfer process in ion–Na(3s, 3p) collisions. Systematic experimental investigations with a range of simple ions reveal a similar behavior of the electron-transfer cross-section parameters as a function velocity. The experimental findings are compared with atomic and molecular orbital calculations.