A new version of the classical over-barrier model for multiple-electron capture in slow collisions between ions and atoms is described. This version accounts for the different ways in which an exchange of a certain number of electrons can occur. Since no adaptable parameter is involved this model has predictive power. Model predictions of absolute multiple capture cross sections are compared with experiment and are found to be in good agreement. Some dynamic effects are accounted for by introducing a velocity-dependent minimum energy uncertainty. Predicted widths of energy gain spectra and of the spectra of autoionisation electrons are found to be in reasonable agreement with experiment.

https://iopscience.iop.org/article/10.1088/0022-3700/19/18/021/pdf

A classical model for multiple-electron capture in slow collisions of highly charged ions with atoms

High-resolution recoil-ion momentum spectroscopy (RIMS) is a novel technique to determine the charge state and the complete final momentum vector of a recoiling target ion emerging from an ionizing collision of an atom with any kind of radiation. It offers a unique combination of superior momentum resolution in all three spatial directions of with a large detection solid angle of . Recently, low-energy electron analysers based on rigorously new concepts and reaching similar specifications were successfully integrated into RIM spectrometers yielding so-called `reaction microscopes'. Exploiting these techniques, a large variety of atomic reactions for ion, electron, photon and antiproton impact have been explored in unprecedented detail and completeness. Among them kinematically complete experiments on electron capture, single and double ionization in ion - atom collisions at projectile energies between 5 keV and 1.4 GeV have been carried out. Double photoionization of He has been investigated at energies close to the threshold up to . At the contributions to double ionization after photoabsorption and Compton scattering were separated kinematically for the first time. These and many other results will be reviewed in this paper. In addition, the experimental technique is described in some detail and emphasis is given to envisaging the rich future potential of the method in various fields of atomic collision physics with atoms, molecules and clusters.

/pdf/recoil-ion-momentum-spectroscopy-2fdjshphs1.pdf

Recoil-ion momentum spectroscopy

The semiclassical close-coupling description of atomic collisions: Recent developments and results

State-selective electron capture in atom-highly charged ion collisions

The ion detection efficiency of microchannel plates (MCPs)

Cross sections for one-electron transfer from a He atom into the fully stripped, hydrogenlike, heliumlike, and lithiumlike ${\mathrm{B}}^{q+}$, ${\mathrm{C}}^{q+}$, ${\mathrm{N}}^{q+}$, ${\mathrm{O}}^{q+}$, ${\mathrm{F}}^{q\ensuremath{-}}$, ${\mathrm{Ne}}^{q+}$ ions, and also highly stripped ${\mathrm{S}}^{q+}$ ions have been measured at the energy range of $1.5q\ensuremath{-}3.0q$ keV. The measured cross sections are nearly independent of the collision energy with a few exceptions, and most of the cross sections measured are about (1\ensuremath{\sim}4)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$, but the cross sections for ${\mathrm{B}}^{4+}$, ${\mathrm{C}}^{4+}$, and ${\mathrm{N}}^{4+}$ ions are very small in the energy range studied. When the cross sections measured are plotted as a function of the ionic charge $q$ of isoelectronic projectile ions, strong oscillations in the cross sections are observed. As a first approximation, this oscillatory behavior can be explained in terms of the classical one-electron model.

Cross sections for one-electron capture by highly stripped ions of B, C, N, O, F, Ne, and S from He below 1 keV/amu

Cross sections for single electron capture from He atom by highly stripped, C q + , N q + , O q + , F q + , Ne q + ( q =4–9) and Kr q + ( q =10–25) ions have been calculated using the multichannel Landau-Zener model. The collision energy is 600 eV/amu except for Kr q + , whose energy is q ×1 keV. The selective electron capture into a single or at most two n -shells is predicted for the cases of q ≤9. The n -distributions obtained by the present calculation are quite consistent with our earlier observation and the total cross sections agree reasonably well with the measured data in spite of the simple model. In the case of Kr q + , where q is larger than 10, more and more shells can be populated and the total cross sections increase monotonically with the increase of q .

Landau-Zener Model Calculations of One-Electron Capture from He Atoms by Highly Stripped Ions at Low Energies

Translation-energy spectra of charge-state-changed projectile ions scattered in the forward direction in collisions of ${\mathrm{C}}^{q+} (q=5,4)$, ${\mathrm{N}}^{q+} (q=6,5)$, and ${\mathrm{O}}^{q+} (q=6)$ ions with He atoms have been measured at collision energies of $q$ and $2q$ keV. All the product peaks observed in the spectra come from exothermic electron-capture processes. From the measured energy gains of the product ($q\ensuremath{-}1$)---charge-state ions, it has been found that an electron is captured selectively into a single shell with a particular principal quantum number $n=2$ for the incident ${\mathrm{C}}^{4+}$ ion and $n=3$ for the incident ${\mathrm{C}}^{5+}$, ${\mathrm{N}}^{5+}$, ${\mathrm{N}}^{6+}$, and ${\mathrm{O}}^{6+}$ ions. This fact is in accord with the prediction of the one-electron classical theory. It has also been revealed that there is good similarity among the energy-spectral patterns obtained for the ions having the same charge $+q$, irrespective of ionic species; such a similarity results from the similarity among diabatic potential curves for the collision systems of the $q$---charge-state ions and He. In the case of ${\mathrm{C}}^{4+}$+He collision, the two-electron---capture process into the ground state of ${\mathrm{C}}^{2+}$ occurs more efficiently than the one-electron---capture process at the low energies studied.

Energy-spectroscopic studies of electron-capture processes by low-energy, highly stripped C, N, and O ions from He

Energy spectra of charge-changing projectile ions are measured for one-electron capture by fully stripped C and O ions from He atoms. The electron is selectively captured into a single level of principal quantum number n=3 of C5+ and n=4 of O7+, respectively, at a collision of 0.45 KeV amu-1.

Observation of electron capture into selective state by fully stripped ions from He atom

Transfer ionisation processes are studied for the N7++He and O7++He systems by means of ion beam spectroscopy at 7 keV. The autoionising states (3l3l') of N5+ and (1s3l3l') of O5+ are identified.

T. Iwai

Papers

Cross sections for one-electron capture by highly stripped ions of B, C, N, O, F, Ne, and S from He below 1 keV/amu

Landau-Zener Model Calculations of One-Electron Capture from He Atoms by Highly Stripped Ions at Low Energies

Energy-spectroscopic studies of electron-capture processes by low-energy, highly stripped C, N, and O ions from He

Observation of electron capture into selective state by fully stripped ions from He atom

Two-electron capture into autoionising states of N5+ (3l3l') and O5+ (1s3l3l') in collisions of N7+ and O5+ with He