Classical and Quantum Mechanical Investigations on Charge Transfer in Heavy Ion-Atom Interactions

Graphical and tabulated data and the associated bibliography are presented for cross sections for elastic, excitation, and ionization collisions of H+, H+2, H+3, ArH+, H−, H, and H2 with Ar and of Ar+ and ArH+ with H2 for laboratory energies from 0.1 eV to 10 keV. Where appropriate, drift velocities and reaction or excitation coefficients are calculated from the cross sections and are recommended for use in analyses of swarm experiments and electrical discharges. In the case of H+ in Ar, cross sections for momentum transfer, charge transfer, electronic excitation, and electron production are recommended. Drift velocity calculations predict runaway for H+ in Ar for electric field to gas density ratios E/n greater than 4.3×10−18 V m2. For H+2 in Ar, the cross sections include those for ArH+ formation, charge transfer, electronic excitation, and electron production. Drift velocities and average cross sections are calculated versus E/n. In the case of ArH+ collisions with Ar, only cross sections for ion molecule reactions are recommended. For H− collisions with Ar only collisional detachment data is available. Momentum transfer, electronic excitation, and electron production cross section data are available for collisions of H with Ar. Collisions of H with Ar are of special interest because of the very large cross sections for excitation of the H atoms at low energies. For H2 in Ar cross sections for momentum transfer and excitation of the Hα and Hβ lines are recommended. For Ar+ collisions with H2, cross sections for charge transfer and ion molecule reactions are recommended. Cross sections for proton transfer are available for ArH+ in H2.

The total cross sections for charge transfer in ${\mathrm{Ne}}^{10+}$ + H, ${\mathrm{Si}}^{14+}$ + H, and ${\mathrm{Ca}}^{20+}$ + H collisions are calculated for ion impact energies of 0.025-2000, 0.025-5000, and 0.1-10 keV/amu, respectively, by means of a unitarized-distorted-wave-approximation method. A scaling rule is derived from the results to predict cross section data. The partial cross sections for electron transfer into the individual orbitals around the projectiles are also investigated. The results show that the most probable principal quantum number of the final state is almost independent to impact energy below 100 keV/amu, while with increasing impact energy above 100 keV/amu it decreases considerably. The strong effects of level crossing and momentum transfer are confirmed to appear in the distributions of final-state population over angular momentum quantum number.

A semiclassical approach is used to calculate excitation and charge transfer cross sections in neutral atom-atom collisions.

Classical (CTMC) calculations of single electron capture and single ionization cross sections are carried out for collisions of H+ and C6+ collisions with H2O molecules in the impact energy range 25<E<5000 keV/amu. The calculation employs a multi‐center model potential for the interaction of the active electron with the H2O+ core. The results agree with the experimental data when the independent electron event model is applied to evaluate total electron capture and ionization probabilities from the corresponding one‐electron ones.

The fraction of excited ions present in O+ ion beams produced by impact of 60-eV electrons on various oxygenated molecules has been determined approximately 23 μsec after formation. The technique employed involves the measurement of apparent rate coefficients for charge-transfer reactions of O+ to N2 and CO at very low kinetic energies (∼0.3 eV) in a tandem mass spectrometer. Under these conditions, charge transfer of O+(4S) is endothermic and the formation of N2+ and CO+ products is due solely to excited O+ ions in the reactant beam. By normalizing the rate coefficients for the reactions of O+ from the several sources to that for an O+ beam for which the excited ion abundance is known, the fractional abundance of O+* in each of the respective ion beams is calculated. These fractions for O+ beams from the indicated sources were found to be: CO2, 0.04; N2O, 0.43; NO2, 0.34; H2O, 0.90. The fractional abundance data are utilized for the study of the reactions of both ground-state and excited-state O+with Ar and Kr. Ground-state O+(4S) was found to be completely unreactive with Ar even at ion kinetic energies up to 170 eV. The cross section for charge transfer from excited O+ ions to Ar is quite small at very low kinetic energies but increases sharply at energies above E1ab ∼20 eV. Both O+(4S) and O+(2D) undergo charge transfer to Kr over the energy range investigated and a maximum is observed in the cross section for the O+(4S) reaction. The results are qualitatively consistent with the adiabatic hypothesis for nonresonant charge transfer.

Cross sections for charge transfer, neutralization and excitation in H-H and H--H+ collisions are presented in the energy range 1-30 keV. The semiclassical close-coupling approach is used with a two-centre two-electron atomic state expansion and frozen total spin. All details of the two-centre atomic state expansion scheme are given. The basis is expanded onto the bound state of H- and the two-centre H(1s)-H(nlm) states, where n covers the K, L and M shells. A good agreement with experiments is achieved for charge transfer, neutralization and excitation to H(2s) in H-H collisions. Disagreement with previously published close-coupling calculations and experimental data is noted, especially for two-electron charge transfer in H--H+.

A coincidence technique has been used in a fast intersecting beam study of H+-He+ collisions to determine cross sections for charge transfer in the centre-of-mass energy range 60-180 keV. Cross sections for ionisation have also been determined by reference to previously measured total cross sections for He2+ production from the combined processes of charge transfer and ionisation.

An approximate quasiclassical treatment is presented for calculating the cross sections for charge transfer from a neutral alkali-metal atom colliding with a halogen atom (chlorine or fluorine). The electron is treated by the time-dependent perturbation in the two-state approximation. The two states are the ground (or the first-excited) state of alkali-metal atom and the ground state of the halogen negative ion. Charge-transfer cross sections are calculated as a function of relative velocity ($v$) of collision between $v=0.01 \mathrm{and} 5$ a.u. Qualitative features of these cross sections are compared with an earlier work on alkali-metal-oxygen collisions. An asymptotic formula at low velocities of collision $v\ensuremath{\rightarrow}0$ is obtained, which compares with the earlier formula obtained by Bates. At higher velocities cross sections are found to vary as $\frac{1}{{v}^{2}}$, as in the Born approximation.

Charge transfer in collisions Na n + + Cs ( ) is investigated theoretically within a microscopic framework. It is shown that an understanding of the measured charge transfer cross-sections can be obtained only if the competing reaction channels (electronic excitations and fragmentation) are treated simultaneously and, in addition, if the initial temperature of the clusters in the beam is taken into account. The energy dependence of the cross-sections is predicted. An exotic charge transfer channel producing Cs- is found to have a finite probability.

The authors have computed the cross section for charge transfer from atomic hydrogen to the excited 3s level of doubly charged nitrogen, triply charged nitrogen and atomic hydrogen at very low relative collision energies (mcV). A rich resonance structure is found and interpreted in terms of quasi-bound states associated with the classical phenomenon of orbiting. Possible experimental verification of the resonance structure is discussed.

The $R$-matrix theory of Wigner is applied to the description of charge exchange. By making use of the correct coordinates for each arrangement, the boundary conditions are properly satisfied. Unphysical long-range couplings do not appear, and the use of "electronic traveling factors" is avoided. The wave function for different arrangements are nonorthogonal, and are essentially equivalent to the "intersecting waves" of Delos [Phys. Rev. A 23, 2301 (1981)]. It is shown under appropriate simplifying assumptions that the $R$-matrix formalism reduces to the high-energy two-state approximation of Kramers and Brinkman. The main task of the $R$-matrix theory is the determination of the matrix elements of the Hamiltonian between basis functions belonging to different arrangements. This is achieved by methods of functional transfer combined with appropriate simplifications arising from the smallness of $\frac{m}{M}$. This leads to the central result that the transformation of a highly oscillating nuclear radial function from one arrangement to another brings with it a highly oscillating function of the electronic coordinates of the new arrangement. This causes off-diagonal elements of the Hamiltonian matrix to decrease rapidly as the energy increases. Consequently the cross section for charge transfer also decreases with increasing energy.

The cross section for charge transfer between cesium ions and cesium atoms has been determined as a function of primary ion energy from 50 to 4000 ev. At each energy the cross section was obtained from meisurements of the number of slow ions formed along a known length of the fast primary ion beam in passing through cesium vapor, the primary beam current, and the number density of cesium atoms inside the interaction region. The measured cross sections are higher than those of other investigations within the same energy range in which different methods were used, but are consistent with those of an investigation in the energy range 5 to 25 kev. The result of a least-meansquares fit indicates that the cross section may be represented between 50 ev and 4000 ev by the expression Q/sup 1/2/ x 10/sup 8/ = 26.8 - 1/46 1nV, were Q is the cross section (cm/sup 2/) and V is the primary ion beam energy (ev). (auth)

Cross sections for charge transfer between ground state (4S) O+ ions in H2 have been measured within the energy range 0.1-1.0 keV. A novel photoionization source which eliminates problems associated with metastable ions was used and the results resolve the large discrepancies between previous experiments.

We have measured the absolute cross sections for reactions of Xe(+) and Xe(2+) with NH(3) at collision energies in the range from near-thermal to ∼34 and ∼69 eV, respectively. For Xe(+), the cross section for charge transfer, the only exothermic channel, decreases from ∼200Å(2) below 0.1 eV to ∼12Å(2) at the highest energies studied. The production of NH(3) (+) is the only channel observed below 5 eV, above which a small amount of NH(2) (+) is also formed. In Xe(2+) reactions, the main products observed are NH(3) (+) and NH(2) (+). The charge transfer cross section decreases monotonically from ∼80 to ∼6Å(2) over the studied energy range. The NH(2) (+) cross section is similar to the charge transfer cross section at the lowest energies, and exhibits a second component above 0.4 eV, with a maximum of 65Å(2) at 0.7 eV, above which the cross section decreases to ∼30Å(2) at the highest energies studied. At energies above 10 eV, a small amount of NH(+) is also observed in Xe(2+) collisions. Product recoil velocity distributions were determined at selected collision energies, using guided-ion beam time-of-flight methods.

Charge transfer, excitation and evaporation in low energy collisions of simple metal clusters and fullerenes with atomic targets