Alkali-metal-halogen charge-exchange collisions

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.

Theoretical investigations on charge transfer in collisions of fully stripped ions with neutral atoms are exhaustive [1–4]. In contrast, a few theoretical studies [5–10] have so far been made to study charge transfer cross sections in collisions of partially stripped ions with neutral atoms at intermediate and high-energy region. In this respect, the scenario of experimental investigations on partially and fully stripped ions is well balanced. In this connection, works of Goffe et al [11] and Phaneuf et al [12] are worthy of mentioning. Olson and Salop [5] have calculated charge transfer and ionization cross sections by fully and partially stripped ions of Bq+, Cq+, Nq+ and Oq+ (q≥3) from atomic hydrogen in the framework of Classical Trajectory Monte Carlo (CTMC) simulation method in intermediate and high energy region. They have treated the interaction of the active electron with projectile ion as coulombic with an effective charge determined from spectroscopic data. Eichler et al [6] have calculated charge transfer cross sections for the same processes except for Bq+ replaced by Liq+ (q ≥ 3) in OBK- approximation. They have treated the projectile ions as bare ions with asymptotic charge (q). However, they have multiplied the calculated cross sections by a reduction factor obtained from eikonal approximation and successively by Pauli blocking factor.

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.

The elastic scattering cross section of the h0-H+ interaction is calculated in the energy range from 1 to 100 keV using the partial-wave method. Using this method, sharp angular dependences of the cross section are obtained. These angular dependences are then compared with the results of the Born approximation and Rutherford scattering. The cross section in the Born approximation is obtained by exchanging an electron with a proton in the known electron-H0 scattering model. Agreements are obtained between these cross sections at high energy or in the region of large scattering angles. The results of the born approximation fit especially well with the partial-wave method at almost all scattering angles in the high-energy range. When total cross sections are obtained, they are compared with a charge transfer cross section and the effects of symmetry are also discussed.

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)

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.

Collisions between SO2 and O are investigated through Molecular Dynamics/Quasi‐Classical Trajectories (MD/QCT) calculations, for SO2 internal energies and relative collision velocities that are of interests to the atmospheric dynamics study of Io. Three possible dissociation reactions are modeled, and reaction cross sections, σr,MD, and the equivalent variable hard sphere (VHS) cross sections, σVHS,MD, are obtained based on the MD/QCT results. The ratio of σr,MD to σVHS,MD indicate that in high collision velocity regime the dissociation reaction is the dominant process. Reaction probabilities are further obtained by using the sum of the reaction cross section and equivalent VHS cross section as the total collision cross section. This method provides the consistent total collision cross sections and reaction probabilities that can be applied in direct simulation Monte Carlo (DSMC) for large range of total collisional energies whereas the VHS cross section and the reaction probability from the total collision energy (TCE) model cannot be applied in high collision velocity regime that needs to be modeled.

K-shell charwe transfer cross sections have been computed In the Bates-Born formalism and the various approximations common to it for H+, LI+, and B5+ projectiles and He, C, and Ne targets. The cross sections are computed for a variety of representations of the target K-shell orbital and with both Hartree-Fock and "experimental", orbital energies. The cross sections are found to be insensitive to the particular energy when the collision velocity is several times greater than the orbital velocity. The cross section is sensitive to the various approximations particularly at the lower collision energies and for the nearer resonant cases.

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.

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 cross sections for electron stripping of fast helium atom in helium gas and in nitrogen gas have been measured by the initial-growth method. The observed values are considerably smaller than those obtained by Hayden and Utterback using the condenser method. The cross sections for hydrogen atom in hydrogen gas and in nitrogen gas have also been measured. Below 0.5 keV, the present results for the stripping cross sections differ from those obtained by other authors. This is attributed to the improper assumption adopted by these authors that the secondary electron emission coefficients for neutrals are equal to those for ions. These coefficients for neutral particles incident upon a copper surface have been experimentally determined in this work. The effect of re-neutralization and of scattering upon the apparent stripping efficiencies are discussed on the basis of the obtained cross sections for charge transfer and for elastic scattering.

Studies of electron correlations of doubly-excited electrons in hyperspherical coordinates, and differential and total cross sections for charge transfer and ionization in fast ion-atom collisions are reported. (GHT)

A different approach has been developed to measure two-body collision cross sections in the energy range from thermal to several hundred electron volts. Two molecular beams are merged and move in the same direction along a common axis. Ion-neutral reactions are discussed but the techniques could also be used for ion-ion and neutral-neutral collisions. Advantages of the merging beams technique over conventional beam-gas and crossed beam methods include accessibility (with good energy resolution) to the energy region from a few tenths of one to a few electron volts; the possibility of measuring cross sections for two general, labile species; and relative ease in collecting and detecting products for total reaction cross section measurements. The principles of the method and details of the instrument are discussed. A cross section for the resonant charge transfer of Ar was measured. Reasonable agreement with some previous measurements, and other tests, indicate that the basic principles of a merging beams technique are valid and that the apparatus performs satisfactorily.

Charge-transfer cross sections have been examined for Ar+–H2, N2, O2, CO, and NO collisions, in the energy range 0.5–3.0 keV, using time-of-flight techniques in which fast neutral Ar products from the electron transfer processes are measured. Cross sections in Ar+–H2 and N2 systems are comparatively large and decrease with ion kinetic energy while the Ar+–O2, CO, and NO cross sections increase with incident ion kinetic energy. The Ar+ ion beam was composed of 2P3/2 and 2P1/2 states with no evidence of long-lived, electronically excited states participating in these reactions. A multistate impact parameter treatment of atomic ion–diatomic molecule collisions is presented and applied to the Ar+(2P3/2, 2P1/2)−H2(X 1Σ+g, v0′=0) system. The resulting coupled differential equations have been solved numerically, with convergence of the cross sections achieved by inclusion of a comparatively large number of possible product channels in the wavefunction expansion of the system. At low ion kinetic energies both the energy defects and vibrational overlaps determine the population of the product vibrational states while at high kinetic energies the vibrational overlaps control the product-ion vibrational-state distribution. Small-angle scattering dominates the charge-transfer reactions with forward inelastic processes becoming more intense as the ion kinetic energy is increased.

The cross sections of resonant charge transfer between atoms and positive ions for all non-transition-elements in the range of low collision velocities ({lt}10{sup 8} cm/sec) have been calculated by the impact-parameter and close-coupling methods. The calculated results are in fairly good agreement with the experimental results for the elements for which data are available. In these results the relation between the cross sections and the ionization potentials of elements was found, and based on this relation a useful and simple formula for the cross section was successfully obtained.