Electron-impact Ionization Of Atomic Ions Research Articles

Fully relativistic time-dependent close-coupling method for electron-impact ionization of atomic ions

A fully relativistic time-dependent close-coupling method is developed based on Dirac’s covariant formulation of quantum mechanics. The expansion of a one-electron wave function in spin-orbit eigenfunctions yields the well-known coupled Dirac equations in two radial wave functions, while the expansion of a twoelectron wave function in coupled spin-orbit eigenfunctions yields close-coupled Dirac equations in four radial wave functions. The time-dependent Dirac equations are solved directly using numerical methods that avoid the Fermi doubling pathology. Test calculations are carried out using the one-electron coupled equations for j = 1 2 elastic potential scattering from Ne 9+ at 2.00 keV and using the two-electron close-coupled equations for

“Electron impact ionization of helium isoelectronic systems”

We show that the criticism [Eur. Phys. J. D 49, 167 (2008)] of our empirical formula for electron-impact ionization of atomic ions [J. Phys B. 33, 5025 (2000)] is unjustified.

Electron-impact ionization of atomic ions in the Sn and Xe isonuclear sequences

Electron-impact ionization cross-sections for all atomic ions in the Sn and Xe isonuclear sequences are calculated using a semi-relativistic configuration-average distorted-wave method. Contributions to the cross-sections are included from both direct ionization and indirect excitation-autoionization. Branching ratio calculations are carried out for Cu-like Sn 21+and Xe 25+ and Na-like Sn 39+ and Xe 43+ to determine when best to ignore indirect excitation-autoionization contributions due to radiation damping along the isonuclear sequences. Although experiments exist for Xe through to Xe 6+, Xe 8+, and Xe 43+ the configuration-average distorted-wave results only agree well with the Xe 8+ measurements, once metastable states are taken into account and with the Xe 43+ measurements once radiation damping of the excitation-autoionization contribution is accounted for. Temperature-dependent rate coefficients are calculated for each Sn and Xe ionization stage and then put in a collisional-radiative format that should prove useful in modelling astrophysical and laboratory plasmas.

Electron-impact ionization of atomic ions in the W isonuclear sequence

Electron-impact ionization cross sections for all atomic ions in the W isonuclear sequence are calculated using a variety of theoretical methods. For the direct ionization process, a semirelativistic configuration-average distorted-wave method is used for low to moderately charged ions, while a fully relativistic subconfiguration-average distorted-wave method is used for highly charged ions. For the indirect ionization process of excitation autoionization, a semirelativistic configuration-average distorted-wave method is used for the bulk of the transitions, but a semirelativistic level-resolved distorted-wave method is used for selective strong transitions that may straddle the ionization threshold. For moderately charged ions it is important to include radiation damping of the excitation-autoionization process through explicit calculation of autoionization branching ratios. Checks are made on the theoretical predictions by comparison with available crossed-beams experimental measurements, which only exist for low stages of ionization. The ionization cross sections for the entire W isonuclear sequence are converted to temperature-dependent rate coefficients and put in a collisional-radiative format that should prove useful in modeling laboratory plasmas that contain W impurities.

Experimental and theoretical study of electron-impact ionization of atomic ions in the Sm isonuclear sequence

Experimental measurements and theoretical calculations of absolute cross sections are carried out for the electron-impact ionization of atomic ions in the Sm rare-earth-metal isonuclear sequence. Absolute cross sections for ${\mathrm{Sm}}^{q+}$ ions for $q=1\ensuremath{-}12$ were measured using the electron-ion crossed-beam technique and calculated with the configuration-average distorted-wave method for the charge states $q=4\ensuremath{-}12.$ The theory includes both direct ionization and excitation-autoionization contributions, and includes transitions from both ground and metastable levels. We present the cross sections in an electron-impact energy range from threshold up to 1000 eV for all Sm ions up to ${\mathrm{Sm}}^{12+}.$ These systems are extremally complex, but the configuration-average method, when combined with statistical averaging of the cross sections over the many levels, provides results that are in overall good agreement with the experimental measurements. The single-ionization cross sections are dominated by contributions from indirect mechanisms of excitation-autoionization in the low-energy region.

Electron-impact single ionization of atomic ions in the Ga isonuclear sequence

Theoretical distorted-wave calculations and experimental crossed-beam measurements are carried out for the electron-impact ionization of atomic ions in the Ga isonuclear sequence. For ${\mathrm{Ga}}^{+}$ and ${\mathrm{Ga}}^{2+}$ the indirect process of $3d$ subshell excitation followed by autoionization is calculated to make a significant contribution to the total ionization cross section near threshold. For ${\mathrm{Ga}}^{3+},$ ${\mathrm{Ga}}^{4+},$ and ${\mathrm{Ga}}^{5+}$ the total ionization cross section is calculated to be dominated by direct ionization of the $3d$ subshell. For ${\mathrm{Ga}}^{6+},$ ${\mathrm{Ga}}^{7+},$ ${\mathrm{Ga}}^{8+},$ and ${\mathrm{Ga}}^{9+}$ the indirect process of $3p$ subshell excitation followed by autoionization is calculated to make a sizable contribution to the total ionization cross section. The distorted-wave predictions for the Ga ions are generally confirmed by the reasonable agreement found between theory and experiment along the isonuclear sequence.

Electron-impact ionization of multiply charged manganese ions

Distorted-wave calculations are carried out for the electron-impact ionization of atomic ions in the Mn isonuclear sequence. Detailed level to level calculations are performed for the dominant excitation-autoionization contributions. The validity of the configuration-average approach is studied and used to calculate direct ionization and higher n excitation-autoionization, when the level to level approach proves computationally too demanding. A combination of the two methods is used to analyze the recent crossed-beams experimental measurements of ${\mathrm{Mn}}^{5+},$ ${\mathrm{Mn}}^{6+},$ ${\mathrm{Mn}}^{7+},$ and ${\mathrm{Mn}}^{8+}$ by Rejoub and Phaneuf [Phys. Rev. A 61, 032706 (2000)]. The comparison between theory and experiment indicates that a large fraction of the initial population of each measured ion is in metastable states of excited configurations.

Time-dependent close-coupling calculations of correlated photoionization processes in helium

Various correlated photoionization processes in helium are calculated by direct solution of the time- dependent Schrodinger equation. An inhomogeneous set of time-dependent close-coupled partial differential equations are partitioned on a numerical lattice for easy implementation on massively parallel computers. Projection of the time evolved wave function onto lattice eigenstates for He 1 yields cross sections for photo- ionization with excitation and double photoionization. The computational results are compared with recent experimental measurements. @S1050-2947~98!07701-4# PACS number~s!: 32.80.Fb I. INTRODUCTION An accurate description of the correlation between two electrons moving in the long-range Coulomb field of a third body, as found in the double photoionization of helium, re- mains a challenging theoretical problem. However, the diffi- culties are somewhat mitigated if examined in the time do- main. As pointed out by Bottcher @1#, the time evolution of a wave function localized in space, as found in the ground state of helium, obviates the need for answers to questions about the asymptotic form of the wave function in coordinate space or its singularities in momentum space. In this paper a time-dependent close-coupling method @2,3# developed to study the electron-impact ionization of atomic ions @4# has been extended to include radiative dipole coupling. This larger set of coupled partial differential equations may then be time propagated on a lattice to yield accurate cross sec- tions for a variety of correlated photoionization processes in two-electron atomic systems. We begin with test calculations for the photoionization of ground-state helium above the complete fragmentation threshold. Recent synchrotron light experiments have nar- rowed the measurement uncertainties both for photoioniza- tion with excitation @5# and double photoionization @6-8# of ground-state helium so as to provide benchmarks for the de- velopment of new theoretical methods. Additional compari- sons may be made with the vast number of time-independent computational theories developed to understand correlated processes in the photoionization of helium. The most popular methods for photoionization with excitation are based on many-body perturbation theory @9,10# and standard R-matrix theory @11,12#. Recent calculations for double photoioniza-

Correlated transitions in the electron-impact ionization of Li+

Atomic collision processes that proceed through electron correlation are examined in the context of the electron-impact ionization of atomic ions. Contributions to the ionization cross section from simultaneous double excitation followed by autoionization are calculated for ${\mathrm{Li}}^{+}$ in a close-coupling approximation. Contributions from simultaneous double excitation with capture followed by simultaneous double autoionization, which proceed through triply excited states, are also calculated for ${\mathrm{Li}}^{+}$ using high-order perturbation theory. Both calculated cross sections are then compared with recent high-resolution crossed-beams experimental measurements.