Total Cross Sections For Double Ionization Research Articles

DoubleL3Mionization of Pd induced by impact with medium-energy electrons

The electron-induced ${L}_{3}M$ two-step double ionization cross sections of metallic Pd were determined experimentally for incident electron beam energies ranging from the double ionization threshold up to 18 keV. The double ${L}_{3}M$ ionization cross sections were derived from the intensity ratios (${I}_{L\ensuremath{\alpha}M}$:${I}_{L\ensuremath{\alpha}}$) of the resolved $M$ satellites to the parent diagram lines. The sample was bombarded with monoenergetic electrons from an energy-tunable 20-kV electron gun. The diagram and $M$-satellite x-ray lines were measured by means of high-resolution x-ray spectroscopy, using a reflection-type von Hamos bent crystal spectrometer. The two-step partial cross sections were determined by subtracting from the measured total double ionization cross sections the contributions due to the shake process and ${L}_{1}$-${L}_{3}{M}_{4,5}$ Coster-Kronig transitions. Despite the thick target employed in the present study, the dependence of the two-step cross sections on the incoming electron energy could be derived using a target slice decomposition method. It is shown that the obtained energy dependence can be well reproduced by the semiempirical parametrization model of Pattard and Rost.

Experimental study of cross-section ratios in the collisions of Cq+ and Oq+ (q = 1–4) on atomic helium in strong-interaction region

We have measured the cross-section ratios of helium induced by Cq+ and Oq+ (q = 1–4) in an energy range from 20 keV/amu to 500 keV/amu, and obtained the two-dimensional spectra by employing the coincidence method combined with the MPA-3 data acquisition system. Hence, we obtain the ratios of total single-ionization cross-sections (SI, SC, SLSI, and DLSI), total double-ionization cross-sections (DI, DC, TI, SLDI, and DLDI) and cross-sections of every process (SI, SC, SLSI, DLSI, DI, DC, TI, SLDI, and DLDI), which induce the single-ionization and double-ionization, to the total cross sections respectively. The competitive relations between the reaction-channels and the experimental data law of each reaction-channel are revealed explicitly, and the qualitative explanations involved in those results are also presented accordingly.

Electron impact double ionization cross sections of light elements

A simple user-friendly semiempirical model is proposed to calculate electron impact double ionization cross sections of He, Li, Li+, B+, C+, C3+, O, O2+, O3+, Ne, Ne+, Ne2+, Na, Mg, Al3+, S, and Arq+ (q=0–7) targets for the incident electron energies from threshold to 106 eV. The contributions in the total double ionization cross sections from the direct double ionization and inner-shell ionization processes are taken into account on the basis of experimental data considered. The results of the present analysis are compared with the available experimental data and theoretical calculations. The model is found successful for the description of experimental cross sections. Since, this model may be a prudent selection to meet the demand level in plasma modeling due to its simple inherent structure.

Double ionization of helium by fast bare ion collisions

A time-dependent close-coupling method is developed to treat the double ionization of helium by fast bare ion collisions. At high incident energies, charge transfer to the projectile is quite small, so that the two-electron wavefunction remains centred on the target, subject to a time-dependent projectile interaction. A multipole expansion of the projectile–atom interaction includes monopole, dipole, quadrupole and octopole terms. Time-dependent close-coupling calculations are carried out for α + He collisions at incident energies greater or equal to 1.0 MeV amu−1. Over 100 coupled channels are needed to obtain total double ionization cross sections that are in good agreement with recent non-perturbative basis-set coupled channels calculations and absolute experimental measurements.

Reply to Comment on `Asymptotic behaviour of the totalcross section for double ionization of helium-like ions byelectrons'

The appearance of the negative slope in the Bethe plot of total crosssection for electron impact double ionization of helium is discussed.

Comment on `Asymptotic behaviour of the totalcross section for double ionization of helium-like ions by electrons'

Defrance et al (Defrance P, Kereselidze T M, Noselidze I L andTzulukidze M F 2001b J. Phys. B: At. Mol. Opt. Phys. 34 4957-68; Defrance P, Kereselidze T, Noselidze I andTzulukidze M 2001a 22nd Int. Conf. on Photonic, Electronic,and Atomic Collisions (Santa Fe, CA) (abstracts of contributedpapers) p 315) have reported calculations of theelectron-impact double-ionization cross section for helium that display a markedly different high-energy behaviour than do most ofthe published experimental data and they contend that newprecise measurements are needed. The results presented hereconfirm the correctness of the more recent experimental dataand indicate that revision of the theory is required.