Charge Transfer Cross Sections Research Articles

Charge transfer and Coulomb fragmentation in slow collisions of Xe25+ ions with Ar dimers

We have evaluated removal and charge transfer cross sections for Xe25+–Ar2 collisions at the impact velocity v=0.3a.u. The theoretical method includes the many-electron aspect of the problem and makes use of the classical molecular dynamics (CMD), which includes over-barrier (OB) and tunneling (TU) mechanisms. We have studied the Coulomb fragmentation of the dimer and showed the preference for asymmetric channels.

Differential Cross Sections for Charge Transfer in He-Like System (Li^+, Be^(2+), B^(3+), C^(4+), N^(5+), O^(6+))-Hydrogen Atom Collisions

Differential cross sections for charge transfer have been calculated for a He-like system (Li^+, Be^(2+), B^(3+), C^(4+), N^(5+), O^(6+)) and hydrogen atom collisions in energies ranging from 0.1 to 100 keV using the classical trajectory Monte Carlo method (CTMC). Interactions of the active electrons with the projectile ions have been described by model potentials. The differential cross sections at angles near the diffraction limit (＜0.1 degree) in all systems show a forward peak followed by an asymptotic fall at higher angles.

New Light Shed on Charge Transfer in FundamentalH++H2Collisions

There is no consensus on the magnitude and shape of the charge transfer cross section in low-energy H+ + H2 collisions, in spite of the fundamental importance of these collisions. Experiments have thus been carried out in the energy range 15≤E≤5000 eV. The measurements invalidate previous recommended data for E≤200 eV and confirm the existence of a local maximum around 45 eV, which was predicted theoretically. Additionally, vibrationally resolved cross sections allow us to investigate the evolution of the underlying charge transfer mechanism as a function of E.

A classical analogue for adiabatic Stark splitting in non-hydrogenic atoms

For highly excited low-ℓ states of atoms, a rising electric field causes a mixing between angular momenta that gives rise to Stark states. A relatively simple situation occurs if the electric field is not strong enough to mix states with adjacent principle quantum numbers. If the initial state has slightly lower (higher) energy than the degenerate manifold, then the state adiabatically connects to a Stark state with the electron on the low (high) potential energy side of the atom. We show that purely classical calculations for non-hydrogenic atoms have an adiabatic connection to extreme dipole moments similar to quantum systems. We use a simple map to show that the classical dynamics arises from the direction of the precession of the Runge–Lenz vector when the electric field is off. As a demonstration of the importance of this effect, we perform classical calculations of charge exchange and show that the total cross section for charge transfer and for ionization strongly depend on whether or not a pure Coulomb potential is used.

Ionization cross section data of nitrogen, methane, and propane for light ions and electrons and their suitability for use in track structure simulations

Track structure Monte Carlo simulations are frequently applied in micro- and nanodosimetry to calculate the radiation transport in detail. The use of a well-validated set of cross section data in such simulation codes ensures accurate calculations of transport parameters, such as ionization yields. These cross section data are, however, scarce and often discrepant when measured by different groups. This work surveys literature data on ionization and charge-transfer cross sections of nitrogen, methane, and propane for electrons, protons, and helium particles, focusing on the energy range between 100 keV and 20 MeV. Based on the evaluated data, different models for the parametrization of the cross section data are implemented in the code ptra, developed for simulating proton and alpha particle transport in an ion-counting nanodosimeter. The suitability of the cross section data is investigated by comparing the calculated mean ionization cluster size and energy loss with experimental results in either nitrogen or propane. For protons, generally good agreement between measured and simulated data is found when the Rudd model is used in ptra. For alpha particles, however, a considerable influence of different parametrizations of cross sections for ionization and charge transfer is observed. The ptra code using the charge-transfer data is, nevertheless, successfully benchmarked by the experimental data for the calculation of nanodosimetric quantities, but remaining discrepancies still have to be further investigated (up to 13% lower energy loss and 19% lower mean ionization cluster size than in the experiment). A continuation of this work should investigate data for the energy loss per interaction as well as differential cross section data of nitrogen and propane. Interpolation models for ionization and charge-transfer data are proposed. The Barkas model, frequently used for a determination of the effective charge in the ionization cross section, significantly underestimates both the energy loss (by up to 19%) and the mean ionization cluster size (up to 65%) for alpha particles. It is, therefore, not recommended for particle-track simulations.

Charge transfer in cold Yb++Rb collisions

Charge-transfer cold Yb$^+$ + Rb collision dynamics is investigated theoretically using high-level {\it ab initio} potential energy curves, dipole moment functions and nonadiabatic coupling matrix elements. Within the scalar-relativistic approximation, the radiative transitions from the entrance $A^1\Sigma^+$ to the ground $X^1\Sigma^+$ state are found to be the only efficient charge-transfer pathway. The spin-orbit coupling does not open other efficient pathways, but alters the potential energy curves and the transition dipole moment for the $A-X$ pair of states. The radiative, as well as the nonradiative, charge-transfer cross sections calculated within the $10^{-3}-10$ cm$^{-1}$ collision energy range exhibit all features of the Langevin ion-atom collision regime, including a rich structure associated with centrifugal barrier tunneling (orbiting) resonances. Theoretical rate coefficients for two Yb isotopes agree well with those measured by immersing Yb$^+$ ion in an ultracold Rb ensemble in a hybrid trap. Possible origins of discrepancy in the product distributions and relations to previously studied similar processes are discussed.

Energy-dependent relative charge transfer cross sections of Cs++ Rb(5s, 5p)

Magneto optical trap recoil ion momentum spectroscopy is used to measure energy-dependent charge exchange cross sections in the Cs+ + Rb(5s, 5p) system over a range of projectile energies from 3.2 to 6.4 keV. The measurements are kinematically complete and yield cross sections that are differential in collision energy, scattering angle, and initial and final states.

Atomic and Molecular Databases and Data Evaluation Activities at the National Institute for Fusion Science

We have constructed and opened atomic and molecular (AM) numerical databases for collision processes important for fusion research. Our databases are accessible through the Internet; the data are retrievable and are displayed as a table or a graph. The databases have been used for data evaluation. Critical assessments of AM data have been carried out since 1978 for electron impact ionization and excitation cross sections, rate coefficients, and charge-transfer cross sections of atom-ion collisions, for helium, carbon, oxygen, etc. Evaluated data are fitted to analytic formulas that have physically correct asymptotic behavior. As another type of evaluation, recommended data sets were selected for electron impact excitation rate coefficients of Fe atoms and ions. Because a large amount of data exists, recommended data are not fitted to analytic formulas, but all data are available as electronic files via the Internet. In addition to AM data, physical sputtering yields and backscattering coefficients are also stored as databases, and empirical formulas have been obtained since the 1980s. All evaluated data are published as research reports of the Institute for Plasma Physics of Nagoya University and the National Institute for Fusion Science of Japan. It is important to establish a systematic way for data evaluation by international collaborations to develop an evaluated AM database required for fusion research.

Investigation of charge transfer and ionization in He-like systems (Li+, Be2+, B3+, C4+, N5+, O6+)-hydrogen atom collisions in Debye plasmas

The charge transfer and ionization cross sections have been calculated for He-like system (Li+, Be2+, B3+, C4+, N5+, O6+) and hydrogen atom collisions in Debye plasmas for energies ranging from 1 to 500 keV using the classical trajectory Monte Carlo method. Interactions of the active electrons with the projectile ions have been described by model potentials. Cross sections are determined in both screening and unscreening environments, and a comparative study between both environments has been carried out. In particular, an interesting feature of sudden increase in the ionization cross sections at lower velocities is also observed in all the systems like pandey et al. [M. K. Pandey et al., Phys. Plasmas 19, 062104 (2012)] calculations for O8+ + H collision. The feature of sudden increase in ionization cross sections at lower velocities and the effect of plasmas condition on it are explained in terms of the classical trajectory framework. We have found the cross sections for both capture and ionization are dependence on Debye screening lengths throughout the collision energies range, but are particularly pronounced at low projectile collisions energies. The calculated cross sections for the unscreened case are found in reasonable agreement with available experimental and theoretical results.

Electron transfer in collisions of keV potassium ions with methane molecules

Absolute total electron transfer cross sections have been measured for the K+–CH4 system, at impact energies 0.5–3.5keV. The charge transfer cross sections show a monotonic increasing behaviour as a function of the incident energy. Semiempirical calculation is in good agreement with the present cross-section data.

Charge-Transfer Cross Sections of Slow Doubly and Triply Charged Carbon Ions from CO and CO<sub>2 </sub>Molecules

collisions with CO and CO2 molecules in the energy range of 0.35 to 3.0 keV per initial charge number based on the initial growth rate method. Most of the present single- and multiple-charge-transfer cross sections show weak energy dependence over the observed collision energy range. For CO2 molecules, the present data smoothly join with the previously measured data in the energy range greater than 10 keV. The cross sections for total charge transfer, which are summations of single- and multiple-charge-transfer cross sections, are compared with a simple over-barrier model and available scaling laws.

Isotope Effect on Charge Transfer Cross Sections of Slow <sup>7</sup>Li<sup>+ </sup>Ions in Collisions with H<sub>2</sub>, HD, and D<sub>2 </sub>Molecules

Isotope Effect on Charge Transfer Cross Sections of Slow <sup>7</sup>Li<sup>+ </sup>Ions in Collisions with H<sub>2</sub>, HD, and D<sub>2 </sub>Molecules

Single- and double-charge transfer in slow He2+–He collisions

The single- and double-electron capture processes in He2+–He collisions are investigated by the fully quantum-mechanical molecular orbital close-coupling method employing a basis containing 15 gerade and 14 ungerade molecular states. The energies and wavefunctions of He22+ molecular states included in the study are determined ab initio by the multireference single- and double-excitation configuration interaction method. The dominant capture mechanisms are discussed and the integral and differential charge transfer cross sections are calculated in the energy range of 0.0005–17.5 keV/u and compared with other available experimental and theoretical results.

State-selective charge exchange in slow collisions of Si3+ ions with H atoms: A molecular state close coupling treatment*)

Charge transfer cross sections are calculated by employing both the quantal and semiclassical ε(R) molecular orbital close coupling (MOCC) approximations in the adiabatic representation and compared with other theoretical and experimental results

Charge transfer and fragmentation in C60 + C6+ collisions

We have evaluated charge transfer and fragmentation cross sections in C60+C6+ collisions. The collision has been studied using a semi-classical model in which the electronic degrees of freedom are quantum mechanically treated. For the fragmentation we have used statistical mechanics based methods. Competition between evaporation and fission (C2 vs C2+ emission) has been studied as a function of the charge of the parent C60q+ and the energy deposited in the collision.

State-selective charge transfer and excitation in ion-ion interactions at intermediate and high energies

Boundary Corrected Continuum Intermediate State (BCCIS) approximation and Classical Trajectory Monte Carlo (CTMC) methods are applied to calculate the charge transfer and excitation cross sections for ion-ion collisions.

Localized Emitting State and Energy Transfer Properties of Quadrupolar Chromophores and (Multi)Branched Derivatives

In order to better understand the nature of intramolecular charge and energy transfer in multibranched molecules, we have synthesized and studied the photophysical properties of a monomer quadrupolar chromophore with donor-acceptor-donor (D-A-D) electronic push-pull structure, together with its V-shaped dimer and star-shaped trimers. The comparison of steady-state absorption spectra and fluorescence excitation anisotropy spectra of these chromophores show evidence of weak interaction (such as charge and energy transfer) among the branches. Moreover, similar fluorescence and solvation behavior of monomer and branched chromophores (dimer and trimer) implies that the interaction among the branches is not strong enough to make a significant distinction between these molecules, due to the weak interaction and intrinsic structural disorder in branched molecules. Furthermore, the interaction between the branches can be enhanced by inserting π bridge spacers (-C═C- or -C≡C-) between the core donor and the acceptor. This improvement leads to a remarkable enhancement of two-photon cross-sections, indicating that the interbranch interaction results in the amplification of transition dipole moments between ground states and excited states. The interpretations of the observed photophysical properties are further supported by theoretical investigation, which reveal that the changes of the transition dipole moments of the branched quadrupolar chromophores play a critical role in observed the two-photon absorption (2PA) cross-section for an intramolecular charge transfer (ICT) state interaction in the multibranched quadrupolar chromophores.

Aggregation effects in proton collisions with water dimers

Charge transfer cross sections in proton collisions with water dimers are calculated using an ab initio method based on molecular orbitals of the system. Results are compared with their counterpart in proton-water collisions to gauge the importance of intermolecular interactions in the cross sections.

Nonradiative charge transfer in collisions of protons with rubidium atoms

The nonradiative charge-transfer cross sections for protons colliding with Rb(5s) atoms are calculated by using the quantum-mechanical molecularorbital close-coupling method in an energy range of 10−3 keV–10 keV. The total and state-selective charge-transfer cross sections are in good agreement with the experimental data in the relatively low energy region. The importance of rotational coupling for chargetransfer process is stressed. Compared with the radiative charge-transfer process, nonradiative charge transfer is a dominant mechanism at energies above 15 eV. The resonance structures of state-selective charge-transfer cross sections arising from the competition among channels are analysed in detail. The radiative and nonradiative charge-transfer rate coefficients from low to high temperature are presented.

Electron capture cross section in collision of multi-charged neon ions with ground state hydrogen and helium

The classical trajectory Monte Carlo method and the post form of three-body boundary corrected continuum intermediate state (BCCIS-3B) approximation are employed to calculate the cross sections for total and state-selective electron capture in collision of highly charged Neq+ ions with ground state hydrogen atom in the intermediate to high energy region. In both these methods, the active electron interactions with the partially stripped neon ions are described by a model potential containing both a long-range part and a short-range part. We have also calculated the double electron-capture cross sections in collision of fully stripped neon ion with helium atom in the energy range 80–2,000 keV/amu using the post-form of four-body BCCIS approximation (BCCIS-4B). In BCCIS formalism, the intermediate continuum state of the active electrons with the projectile ion has been taken into account as the projectile charge is greater than the target charge. In addition, state-selective charge transfer cross sections are given in tabular and graphical form.