Transitions In Slow Collisions Research Articles

Mechanisms of non-adiabatic charge-exchange transitions in slow collisions of W ions with He, Ar and Kr atoms

The study of slow collisions of heavy particles is a challenging task from both experimental and theoretical points of view. A powerful tool for the theoretical description of these collisions is the adiabatic theory of transitions in slow collisions developed by Solov’ev (1989), which is applied here to study low-energy charge exchange between tungsten ions and inert-gas atoms at 0.01–1 keV/u. It is found that the main mechanism of charge-exchange transitions in collisions of W+ ions with Ar and Kr atoms at energies below 1 keV/u is the rotational coupling associated with internuclear axis rotation in close collisions, while charge exchange between W8+ ions and He atoms is mainly due to the radial Landau–Zener type transitions. For all cases, potential curves as a function of the internuclear distance are calculated together with the charge-exchange cross sections. The cross sections obtained are compared with experimental data, showing good agreement and explaining the mechanisms of the transitions.

Collisions of Be, Fe, Mo and W atoms and ions with hydrogen isotopes: electron capture and electron loss cross sections

This work is a continuation of an investigation of the collisional properties of heavy-ion plasma impurities and the elements used for the plasma facing components in fusion devices. Results on the charge-changing cross sections for W atoms and ions are published in (Tolstikhina et al 2012 J. Phys. B: At. Mol. Opt. Phys. 45 145201). Here we present the electron loss and electron capture cross sections for collisions of Be, Fe and Mo atoms and their ions with the hydrogen isotopes (H, D, T) calculated in the E = 10 eV/u–10 MeV/u energy range. The calculations are performed, accounting for the multiple-electron loss processes and the cross sections, which can contribute more than 50% to the total loss cross sections. The influence of the isotope effect (mass dependence) (Stolterfoht et al 2007 Phys. Rev. Lett. 99103201) on the capture cross sections is also studied in the frame of an adiabatic theory of transitions in slow collisions. New data on the partial multiple-electron loss cross sections for W and W+ are presented. Calculated cross sections are compared with the available experimental and theoretical data.

Charge-changing collisions of tungsten and its ions with neutral atoms

New experimental and theoretical data on charge exchange (CE) cross sections are presented for low-energy collisions (10–500 eV u−1) of W+ and W2 + ions with H, H2 and He atoms. The CE cross sections are calculated using the ARSENY code based on the hidden crossing method. The isotope effect (mass dependence) in collisions of W+ and W2 + ions with hydrogen isotopes H, D, T is studied in the framework of the adiabatic theory of transitions in slow collisions. Furthermore, the electron loss (EL) and CE cross sections for the energy range of 1–105 keV u−1 are calculated for tungsten and its ions Wq + (q = 0–40) colliding with H, He, N, Ar and W atoms using the computer codes (CAPTURE, DEPOSIT and RICODE) based upon the Born approximation and the classical energy-deposition model. The data obtained can be used for plasma modelling, planning and interpretation of future experiments in fusion devices using tungsten as a material for the plasma-facing components.

Influence of the isotope effect on the charge exchange in slow collisions of Li, Be, and C ions with H, D, and T

The influence of the isotope effect (mass dependence) on the charge-exchange process in low-energy collisions of light ions with hydrogen isotopes (H, D, and T) is studied using the adiabatic theory of transitions in slow collisions developed by E. Solov'ev [Sov. Phys. Usp. 32, 228 (1989)]. Results of the numerical calculations are presented for the charge-exchange probabilities and cross sections of Li, Be, and C ions colliding with hydrogen isotopes and for the inverse reactions.

Inelastic processes in slow collisions of antiprotons with hydrogenic ions

We present a comprehensive theoretical study of the physical processes which govern inelastic transitions in slow collisions of antiprotons with hydrogenic ions. Two-centre - one-electron mechanisms are highlighted. Various channels for ionization and excitation are identified utilizing the theory of hidden crossings. New features of the quasimolecular potentials, caused by the negative charge of the antiproton, are described in detail, with particular attention to the topology of the electronic eigenenergy surface in the plane of complex internuclear distance. The ionization and excitation cross sections are calculated and compared with the results of other theories and recent experiments.

On the interpretation of two electron-one photon transitions in slow collisions between fully stripped ions and solid target

The two electron-one photon transitions occuring in slow collisions of fully stripped neon atoms with solid targets have been interpreted in terms of trapping ofL-shell electrons in bare neon atoms from the solid target and subsequent transitions toK-shell. Experimental X-ray spectra and transition probabilities can be interpreted in terms of actual transitions occurring in such cases explicitly by the present theoretical calculations which takes care of correlation and relaxation effects.

Theoretical study of electron processes in slow He2+-He collisions

Electron excitation and transfer in He2+-He collisions have been studied in an energy interval of 4-65 keV u-1. The general features of these processes are discussed on the basis of two-electron molecular energies. These suggest a common mechanism for single-electron transfer and transfer-excitation transitions in slow collisions, and similarly for excitation and double-transfer transitions. Cross sections are determined within the semiclassical close-coupling method. At low energies, the strongest channel is resonant two-electron transfer. For the other, weaker channels the author finds that the population of any given state in the projectile is about equally strong as the equivalent state in the target. The results from this work compare well with data from a companion experimental study. The author also assesses a few one-electron transitions in collisions with metastable helium.

Electronic Transitions in Slow Collisions of Atoms and Molecules. IV. Multistate Eikonal Approximation for Quasiadiabatic Transitions

The coupled equations of the adiabatic-state expansion method for quasiadiabatic transitions in atomic collisions are reduced in the eikonal approximations to a form that allows straightforward computation. The multistate eikonal approximation is then applied to the ${\mathrm{He}}^{+}(1s)+\mathrm{H}(1s)\ensuremath{\rightarrow}{\mathrm{He}}^{+}(1s)+\mathrm{H}(2p)$ excitation process. The partial and total $2p$-excitation cross sections as well as the polarization of the light emitted by the excited H atoms are calculated. Our results compare well with recent experimental measurements. The importance of final-state coupling is dramatically illustrated by the above $2p$-excitation process. The qualitative features of the nonadiabatic effects are also investigated in the eikonal Born approximation as functions of the position and distance of closest approach of the two adiabatic states.

Electronic Transitions in Slow Collisions of Atoms and Molecules. III. Eikonal Approximation for Nonclassical Scatterings

Characteristic quantum features in atomic collisions are analyzed in the eikonal approximations. Numerical illustrations are given for the (${\mathrm{He}}^{+}$, He) system, using a set of model potentials which provide a reasonable description of the interaction between the ground states of ${\mathrm{He}}^{+}$ and He in the quasiadiabatic (diabatic) limit.

Electronic Transitions in Slow Collisions of Atoms and Molecules. II. Calculations of Wave Functions and Green's Functions in the Eikonal Approximation

Practical techniques are developed for evaluating wave functions and Green's functions using the eikonal approximation. It is assumed that the scattering angle is small. This provides a great simplification in analysis of the trajectory curves, radii of curvature, etc. A sequence of approximations and the use of variational principles are described. Numerical illustrations, particularly for proton-hydrogen-atom scattering, are given for several of the approximations.

Electronic Transitions in Slow Collisions of Atoms and Molecules. I.

The semiclassical approximation is systematically applied to the study of electronic transitions in near-adiabatic collisions of atoms and molecules. The use of the eikonal approximation permits the coupled equations of scattering theory to be reduced to one-dimensional equations defined along classical trajectories. The theory for rearrangement collisions is developed into a form appropriate for use with the eikonal description of heavy-particle motion.