Charge Transfer Processes In Collisions Research Articles

Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Si q+-Ar collisions

A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Si q+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q 1.7/E 0.5 , where E p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j 2 upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σ qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.

Charge-transfer processes in collisions of ground-stateC+ions withH2,D2,CO, andCO2molecules in the energy range from 0.15 to 4.5 keV

Charge-transfer processes in collisions of ${\mathrm{C}}^{+}$ ions with ${\mathrm{H}}_{2},$ ${\mathrm{D}}_{2},$ CO, and ${\mathrm{CO}}_{2}$ molecules have been studied based on joint experimental and theoretical approaches in the collision energy from 0.15 to 4.5 keV. In the present experiment, the ground-state ${\mathrm{C}}^{+}{(}^{2}P)$ ion projectiles have been produced by carefully energy-controlled electron impact to minimize the influence of the metastable-state ions. The observed cross sections are compared with the present theoretical prediction, and while the theoretical results are somewhat smaller than the measurements, they are found to be in reasonable agreement for ${\mathrm{H}}_{2},$ ${\mathrm{D}}_{2},$ and CO above around 1 keV. The present experimental cross sections for CO and ${\mathrm{CO}}_{2}$ are smaller by a factor of 2 to 3 than those of earlier measurements. We provide some remarks on the effect of the metastable-state ions.

Charge-transfer processes in collisions ofH+ions with phosphorus atoms at low energies

We have carried out a theoretical investigation of charge transfer in collisions of ${\mathrm{H}}^{+}$ ions with neutral phosphorus P atoms both in the ground and metastable states at collision energies below 10 keV/u and above 100 eV/u using a molecular representation. Molecular states for the ${\mathrm{PH}}^{+}$ molecule are obtained by employing the ab initio multireference (single- and double-excitation) configuration-interaction method. In calculating charge-transfer cross sections, we have adopted the semiclassical impact-parameter method. The present charge-transfer cross sections from the ground-state P target are found to reach as large as $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}{\mathrm{cm}}^{2}$ at 1 keV/u after slowly increasing from lower energies, and the contribution from ${\mathrm{P}}^{+}{(}^{3}P)$ and ${\mathrm{P}}^{+}{(}^{5}{S}^{o})$ formations to the total are found to be comparable at the energy region where the cross section possesses a maximum.

Elastic and inelastic processes in H++C2H2 collisions below the 1.5-keV regime.

Charge-transfer processes in collisions of H{sup +} ions with C{sub 2}H{sub 6} molecules are investigated theoretically below 10-keV collision energies within a molecular representation. Converged total as well as differential cross sections are obtained in this energy range within a discrete basis of electronic states computed by ab inito methods. The present collision system suggests that the combination of the Demkov-type and Landau-Zener-type mechanisms primarily governs the scattering dynamics for the flux exit from the initial channel. The present charge-transfer cross sections determined are found to agree very well with all available experimental data below a few keV, but begin to deviate above 3 keV, in which the present results slowly decrease, while measurements stay nearly constant. From the study of the electronic state calculation, we provide some information on fragmented species, which should help shed some light on the fragmentation mechanism and process of C{sub 2}H{sub 6}{sup +} ions produced after charge transfer. In addition, the vibrational effect of the initial target to charge transfer is examined.

Continuous Energy State Model for Charge Transfer in Collisions of Fully Stripped Ions with Hydrogen Atoms

Charge transfer processes in collisions of fully stripped ions with hydrogen atoms are investigated theoretically. A continuous-energy state model is proposed as a technique of solving equations including a large number of coupled-channels for charge-transferred final states. A numerical result is presented and compared with other theoretical as well as experimental cross sections. Agreement is good in O 8+ +H and Si 14 +H collisions indicating availability of the method for ions with larger charge numbers.

Molecular Resonant Charge-Transfer Processes; H2+–H2 and N2+–N2

A study has been made of the competition between exothermic ion—molecule reactions and resonant charge-transfer processes in collisions of diatomic molecule ions and their parent molecules; H2+–H2 and N2+–N2. Experimental values of resonant charge-transfer cross sections are shown to be smaller than values obtained from calculations using an impact parameter method. Much better agreement between experiment and theory is obtained if competition between ion—molecule reaction and charge transfer is assumed and experimental values of both channels of reaction are summed prior to comparison with theory. The mechanisms of the respective processes are illuminated by an examination of the velocity dependences of charge-transfer cross section for both diatomic systems. With H2+–H2 where reaction producing H3+ is a probable process, in low-velocity collisions, the velocity dependence of charge transfer is essentially that of collisions of ions with unperturbed rectilinear trajectories. In a similar low-energy region, N2+–N2 is not energetically capable of participating in ion—molecule reactions and the velocity dependence of charge-transfer cross section is steeper, characteristic of both orbiting collisions and the larger-impact-parameter rectilinear trajectory collisions. Experimental cross sections for charge transfer and ion or atom transfer reflect probability of reaction but their velocity dependences clearly isolate the range of impact parameters operative for the respective processes.