Resonant charge exchange involving highly excited atoms

Transition of a classical electron between two Coulomb centers is analyzed on the basis of computer simulations. The contribution to the electron transfer cross section from a tunnel electron transition is evaluated taking into account the strong mixing of highly excited electron states due to motion of Coulomb centers. The rate of transition of a highly excited electron between two Coulomb cores with a fixed separation is evaluated together with the cross section of resonant charge exchange in slow collisions. Typical times of change of the electron momentum as a result of electron motion in the field of two Coulomb centers are determined. The text was submitted by authors in English.     

Cross sections for charge exchange of atoms on multiple-charged ions

Processes of charge exchange of Ar^{+ +}(3p ⁵) and Kr^{+ +}(4p ⁵) on He(1s ²) at low collision energies are investigated theoretically. Semiempirical asymptotic calculations of the radial coupling between initial and final states (both neglecting and allowing for the spin-orbit interaction) are presented. The result of semiempirical calculation of the coupling is in reasonable agreement with an earlier ab initio calculation for the system ArHe^{+ +}. The integral cross sections were estimated using the Landau-Zener model. Comparisons are made with available experimental data and numerical quantum calculation.     

Resonant charge exchange in slow collisions involving halogens and oxygen

The coupling of electron momenta is considered for the resonant charge exchange process in slow collisions. Because the electron transfer in this process occurs at large distances between the colliding atomic particles, where ion-atom interactions are relatively weak, we can separate different types of interaction and find the character of coupling of the electron momenta in the quasi-molecule, consisting of the colliding ion and its atom, for real collision pairs. Since the real number of interaction types for colliding particles exceeds that used in the classical Hund coupling scheme, there are intermediate cases of momentum coupling outside the standard Hund scheme. This occurs for the resonant charge exchange involving halogens and oxygen where the quantum numbers of the quasi-molecule in the course of the electron transfer are the total momenta J and j of the colliding ion and atom and the projection M or M_J of the atom orbital or total momentum on the quasi-molecule axis. The ion-atom exchange interaction potential is independent of the ion fine state, and under these conditions, the resonant charge exchange process is not entangled with the rotation of electron momenta, as in case “a” of the Hund coupling. The partial cross section of the resonant charge exchange process depends on quantum numbers of the colliding particles. The average cross sections depend weakly on the coupling scheme.     

Double resonant charge exchange in ion-ion collisions

The process of resonant double charge exchange in low energy ion-ion collisions is considered. The effects of the Coulomb interaction of the nuclei are taken into account. Cross section calculations are performed both for completely and partially stripped projectile ions with 3? Z ? 10.     

Total cross section measurements for charge exchange of He++ ions with He and Ar atoms

Total charge exchange cross sections were measured for He⁺⁺ in He and Ar gas in the energy range from 50 to 540 eV using a single beam apparatus. For He⁺⁺ in He the measured cross section is in agreement with calculations for symmetric resonant charge exchange. For He⁺⁺ in Ar the cross section for charge exchange decreases with decreasing energy below 300 eV. The measured cross section suggests the formation of Ar⁺ ions to be more important at lower energies and the production of Ar⁺⁺ to be dominant at higher energies.     

Effect of the target density on the cross section of charge exchange between fast ions and atoms

When fast X^q+ X^{q^ + } ions collide with atomic or molecular targets, the total charge exchange cross section decreases with increasing target density. This is because the excitation levels of resulting X^{(q - 1)+} X^{(q - 1)^ + } ions are suppressed because of ionization by target atoms. The effect of target density on the total charge exchange cross section may amount to one order of magnitude or more depending on the charge and energy of an incident ion, as well as on the density and inner shell configuration of target atoms. Numerical calculations are performed for partial (in the principal quantum number n) cross sections σ(n) and total cross sections σ_tot=Σ_nσ(n) of charge exchange in the case of collisions of fast multiply charged ions having an energy E in the range 100 keV/u-10 MeV/u with gas or solid targets.     

Isotope separation of Dy atoms using laser excitation followed by charge exchange with Cs+ ions

Dysprosium atoms were isotope selectively excited by cw dye laser light. They were ionized by charge transfer collisions with Cs⁺ ions. The process was found to discriminate well between ground state and excited state atoms. The cross section ration for the two competing processes was determined to be about 10³.     

Ionization potential of atoms and multiply charged ions versus the nuclear charge

The terms of ions and atoms are calculated with a method based on the Bohr model. The ionization potentials of helium-like, lithium-like, and beryllium-like ions are calculated as functions of the nuclear charge and electron quantum numbers. The results calculated are in satisfactory agreement with experimental data. The accuracy of the method is found to rise with the nuclear charge of ions.     

Dependence of the charge transfer between atoms and highly charged ions on the ionization potential of the atoms

Cross sections have been measured for charge transfer in single collisions of 100 keV Xe¹⁰⁺ ions with target atoms B = He, Ne, Ar, Kr, Xe, Cd, Na and Cs. With the decrease of the target ionization potential in the sequence from He (24.58 eV) to Cs (3.89 eV) an overall quadratic increase of the electron capture cross sections was found reaching values up to 1.2 × 10⁻¹³ cm² for the alkali metals.     

Polarization and exchange effects in elastic scattering of electron with atoms and ions

Laser-induced electron diffraction(LIED), in which elastic scattering of the returning electron with the parent ion takes place, has been used to extract atomic potential and image molecular structures with sub-?A precision and exposure time of a few femtoseconds. So far, the polarization and exchange effects have not been taken into account in the theoretical calculation of differential cross section(DCS) for the laser-induced rescattering processes. However, the validity of this theoretical treatment has never been verified. In this work, we investigate the polarization and exchange effects on electron impact elastic scattering with rare gas atoms and ions. It is found that, while the exchange effect generally plays a more important role than the polarization effect in the elastic scattering process, the exchange effect is less important on electron–ion collisions than on electron–atom collisions, especially for scattering in backward direction. In addition, our calculations show that, for electron–atom collisions at incident energies above 50 e V, both the polarization and exchange effects can be safely neglected, while for electron–ion collisions, both the polarization and exchange potentials do not make substantial contributions to the DCS at incident energies above 20 e V and scattering angles larger than 90?. Our investigation confirms the validity of the current LIED method.     

Electron spectroscopy of autoionizing states of oxygen,chlorine and bromine atoms

The autoionizing atomic states are obtained in dissociation Of O₂, Cl₂ and Br₂ molecules excited by either fast neutral He atoms (O₂) or by photons with 21.217 eV energy (Cl₂, and Br₂). Tentative assignment of the autoionizing levels is given for Cl* and for Br* atoms, and a more detailed one for O* atoms.     

Cross section for the resonant charge exchange Cs++Cs at thermal energies

A remeasurement of the cross section for the resonant charge exchange Cs⁺ ?Cs at thermal energies is presented which reduces some of the ambiguities left open in previous studies.     

Stripping of fast oxygen ions colliding with atoms of light elements

Based on the available experimental data and the results of calculations carried out in this paper, cross sections are estimated for single-electron stripping of O ^Z+ (Z=1–7) ions with energies in the range E=0.5–200 MeV/u due to collisions with H, He, N, O, or Ar atoms. Analytical approximations of the cross sections are presented.     

Electron loss of heavy many-electron ions in relativistic collisions with neutral atoms

Electron-loss processes arising in collisions of heavy many-electron ions (like U²⁸⁺) with neutral atoms (H, N, Ar) are considered over a wide energy range including relativistic energies. Various computer codes (LOSS, LOSS-R, HERION, and RICODE), created for calculation of the electron-loss cross sections, and their capability are described. Recommended data on the electron-loss cross sections of U²⁸⁺ ions colliding with H, N, Ar targets and predicted lifetimes of U²⁸⁺ ion beams in accelerator are given. Calculated electronloss cross sections are compared with available experimental data and other calculations.