Spin exchange during collisions of two sodium atoms

Based on data on the singlet (X ¹Σ⁺) and triplet (a ³Σ⁺) potentials describing the interaction of two Na atoms in the ground state, the complex cross sections of spin exchange for the system under investigation are calculated. The obtained cross sections allow one to determine relaxation times, as well as magnetic-resonance frequency shifts caused by spin-exchange Na-Na collisions.     

Ionization of heavy ions in relativistic collisions with neutral atoms

The problem of ionization of ions in ion-ion and ion-neutral relativistic collisions is considered. Formulas for ionization cross sections are derived in the Born approximation in terms of the momentum transfer without allowance for magnetic interactions. Using these formulas implemented in the LOSS-R code, the ionization cross sections are calculated for the K shells of neutral atoms colliding with protons and also for 1s and 2p electrons of multiply charged heavy ions (nuclear charge Z = 80−90) colliding with bare nuclei and neutral atoms. The calculation results are compared with experimental data and calculations of other authors.     

Interplay of charge exchange and projectile excitation in the stopping of swift heavy ions

The electronic energy loss of a dressed ion penetrating through matter is commonly considered as being synonymous with the sum of the excitation energies of the target and the projectile in atomic collisions undergone during the passage. We show that this is not justified in projectile-ionizing collisions and discuss some consequences. Received 23 October 2002 / Received in final form 1st December 2002 Published online 18 February 2003     

Stereo-dynamical ion-pair formation in collisions of highly-charged ions with argon dimers

Multiple ionization process of a rare gas dimer BC collided with a slow highly charged ion A^q+ is investigated with the three-center Coulombic over-barrier model previously developed by the present authors. To reveal stereodynamical effects, we calculate asymmetric ion-pair formation cross sections σ(Q_B,Q_C) as a function of the orientation angle. We introduce a pair of atomic impact parameters b_B and b_C with which we distinguish the near and far sites. Furthermore, we distinguish the forward and backward emitted ions produced as a result of Coulomb explosion. Partial screening effects are also considered.     

Ionization loss of relativistic structural heavy ions in collisions with atoms

A nonperturbative theory of energy loss in collisions between structural, highly charged heavy ions moving at relativistic velocities and atoms is developed. A simple formula for effective deceleration is derived. By structural ions are meant ions containing partially filled electron shells. It is such ions characterized, as a rule, by a significant charge (for example, partially “stripped” uranium ions) that are used in numerous experiments involving the use of modern heavy-ion accelerators.     

Alignment and orientation of charge exchange excitation with polarized projectiles

The alignment and orientation of hydrogenlike excited atoms produced by electron capture in collisions of spin polarized bare atomic nuclei with atomic targets is described in terms of Stokes parameters. TheH(2p)^* excited state formed by spin polarized protons making charge exchange collisions on atomic targets is dealt with extensively for the purpose of illustration. The linear polarization and circular polarization of resulting Lyman-α when polarized protons make electron capture collision on atomic hydrogen target are plotted to compare observable aspects of different theories of electron capture.     

Charge exchange and excitation cross sections at collisions of alpha particles with be-like impurity oxygen ions in a plasma

The charge exchange and excitation cross sections at collisions of alphas with O⁴⁺(1s ²2s ²) impurity atoms in a hot plasma for striking energies E _c varying from 20 keV to 2 MeV are determined for the first time. The cross sections are calculated using the method of close-coupling equations with 13 singlet four-electron quasi-molecular states taken as a basis. The partial cross sections of charge transfer to the 1s, 2s, and 2p states of a He⁺ ion and for O⁴⁺(1s ²2s ²) → O⁴⁺(1s ²2lnl’) (n = 2, 3) electronic excitation of an oxygen ion are found. The maximal value of the charge exchange total cross section roughly equals 2.2 × 10^?16 cm² at E _c ≈ 0.7 MeV. The excitation total cross section has a maximum of ≈ 7.7 × 10^?16 cm² at E _c ≈ 80 keV for single-electron excitation and ≈6.5 × 10^?16 cm² at E _c ≈ 0.7 MeV for two-electron excitation.     

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.     

Ionization of heavy ions in collisions with neutral atoms at relativistic energies

Ionization processes of heavy ions colliding with atoms and ions at relativistic energies are considered. Formulaes for calculating ionization cross sections in the Born approximation using momentum-transfer representation without regard to magnetic interactions are given as well as those in dipole and impulse approximations. Using the LOSS-R [25] and HERION codes, calculations of relativistic cross sections are performed for H-like multiply changed ions with the nuclear charge Z ≈ 80?90, colliding with neutral atoms and for multiply changed uranium ions colliding with protons and carbon atoms. The results of calculations are compared with available experimental data and calculations performed by other authors.     

Dissociative charge exchange in collisions of 10keV H 2 + ions on H2, He,and Ar targets

The velocity distributions of H-H fragment pairs arising from dissociative collisions of 10keV H ₂ ⁺ ions incident on H₂, He, and Ar were measured using a flight-time-difference method. The H ₂ ⁺ ions were produced in an electron impact ion source at two different electron energies, at 100eV and 18eV. The influence of the electron energy on the fragment velocity distributions is studied. Conclusions are drawn on the processes which lead to the formation of neutral fragment pairs. Electron capture into the repulsive b³ Σ _u ⁺ state of H₂ plays a dominant role.     

Dissociative excitation due to collisions of electrons and helium ions with oxygen molecules

The absolute cross sections of luminescence related to atomic and ionic oxygen at dissociative excitation through e-O₂ and He⁺-O₂ collisions are determined. An intense OII line (83.4 nm) is discovered. For e-O₂ collisions, a weak OIII line (70.5 nm) is found. Experimental data for He⁺-O₂ collisions are qualitatively interpreted in terms of the quasi-diatomic approximation.     

Effect of resonance charge exchange between argon ions on the effective sputtering rate in a magnetron discharge

The sputtering rates of various materials in a magnetron ion sputterer are compared. The effective sputtering yields obtained when argon is used as a working gas are given. The difference between the sputtering yields found in this work and those obtained with monoenergetic ion beams is shown to be associated with resonance charge exchange between argon ions and neutral argon gas.     

Ionization by low energy heavy ions in nitrogen,carbon dioxide,argon and hydrocarbon gases

Experimental data on the variation of W, the mean energy expended by a charge particle in producing an ion pair in a gas, with the mass, charge and energy of the particle is examined with a view to discovering how far these variations may be explained in terms of elastic nuclear scattering. In nitrogen and carbon dioxide W appears to depend not only on the elastic nuclear scattering but also on the parameter E/MZ^4/3 for ions other than piotons. In argon any relationship is obscured by apparent discrepancies in the data, although it is possible that the variation may be similar to that in nitrogen and carbon dioxide. The data for the hydrocarbon gases is not so extensive as for the other gases and it may be that the variation of W with the mass and charge of the ion is different from that in nitrogen and carbon dioxide. It is speculated that this difference, if real, is due to super-excited states in the hydrocarbon gases.

Some empirical relationships are suggested as a practical guide for use in dosimetry.     

Determination of alignment tensor components for the H(2p) charge exchange excitation in proton-argon collisions

Alignment tensor components 〈T(L) _KQ ⁺ 〉 have been determined for the H(2p) charge exchange excitation in proton-argon collisions at an incident proton energy of 1.5 keV, and scattering angles Θ _s =4.3°, 4.9°, and 6.0°. It is demonstrated that the measured photon angular distribution cannot be described in terms of only λ and ? parameters.     

Ionization of helium-like ions with excitation of nl states by high-energy photon scattering

The kinetic and spectral characteristics of the complex dielectric constant of a Ce: YAG crystal under laser irradiation in 250–275 nm spectral range are investigated. The lifetimes of free charge carriers and charge carriers, localized at the lattice defects (color centers), are estimated. It was established that photoconductivity signal of the sample is essentially caused by one-photon ionization processes from the ² F _5/2 ground state of Ce³⁺ ions.     

Charge exchange in collisions between heavy low-charged ions

The probabilities and the effective cross sections of collision-induced one-electron charge exchange between singly charged and four-charged heavy Xe, Cs, Ba, Pb, Bi, and U ions at energies E>0.1 keV/u are calculated by a method of multichannel normalization in the impact parameter representation. The cross sections are rather large with a maximum σ_m≈10⁻¹⁵ cm² at relative energies E _m ≈10–30 keV/u. For collision energies E<10 keV/u, the cross sections sharply decrease with growing resonance defect of the reaction. At high energies E>1 MeV/u, the charge exchange proceeds largely by the capture of inner shell electrons of the ionic targets. The charge exchange cross sections calculated for low-charged Xe, Cs, Ba, Pb, Bi, and U ions are compared with available theoretical and experimental data.     

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.