D. C. Gregory

Measurement of the contribution of excitation autoionization to electron-impact ionization of ions: Ti3+, Zr3+, Hf3+, and Ta3+

Measurements were made of the cross section for electron-impact single ionization of the transition-element ions Ti/sup 3 +/, Zr/sup 3 +/, Hf/sup 3 +/, and Ta/sup 3 +/ for an electron-energy range from threshold to 1000 eV. The cross sections are enhanced by as much as a factor of 20 due to excitation-autoionization primarily involving ..delta..n = 0 transitions, np/sup 6/nd/sup m/..-->..np/sup 5/nd/sup m+1/. Comparisons with recent theoretical predictions show reasonable agreement between measured and predicted positions of the autoionization states; however, the magnitudes of the theoretical cross sections are greater than the experimental values by a factor of approximately 2.5.

Electron impact ionisation of nickel ions

Absolute cross section measurements at energies from below threshold to 1500 eV are reported for electron impact ionisation of nickel ions with initial charges 5+, 6+, 7+, 8+, 12+ and 14+. The experimental data are compared with distorted-wave calculations for direct ionisation, which account for 40-80% of the measured peak total ionisation cross sections. The discrepancy is attributed to contributions to single ionisation due to excitation of inner-subshell electrons followed by autoionisation. Ionisation rate coefficients and fitting parameters based on the data are presented for charge states 5+ through 8+.

Electron‐impact dissociation of H3O+

Fragment cross sections for electron impact dissociation of H3O+ into OH+ and O+, and for dissociation of D3O+ into D2O+ have been measured in a crossed beam appartus for electron energies from threshold to 1000 eV. The cross sections for O+ and OH+ rise abruptly at threshold indicating that the mechanism for dissociation is via production of an electronically excited state of H3O+ and direct dissociation into O+ and OH+. At high energy the cross section has a falloff σ∝ln(E)/E expected in the Bethe‐Born approximation. At 200 eV electron energy the cross sections for fragments are: D2O+, σ=6.7±1.8×10−17 cm2; OH+, σ=3.0±0.6×10−17 cm2; O+, σ=7.9±1.6×10−18 cm2. The observed threshold energies for OH+ and O+ production are 14±3 and 19±3 eV, respectively.

Excited state populations and charge-exchange of fast ions in solids

Abstract Excited state populations and charge state fractions of 36 MeV C and 445 MeV Cl ions have been measured for a range of thicknesses of gaseous and solid C targets. Cross-sections for electron capture, loss, excitation and excited state quenching have been determined and these data are found to give a quantitative account of the Bohr-Lindhard density effect model. Implications to stopping power theory are considered.

Electron capture cross sections to hydrogenic states of 1 GeV Ni in solid carbon

Abstract Non-equilibrium charge state distributions and excited state populations for hydrogenic Ni at 1 GeV were measured following excitation in solid carbon. The carbon targets were sufficiently thin to ensure single collision conditions. Cross sections were obtained for electron capture from the carbon target to the various low-lying excited states of hydrogenic Ni ions.

Coulomb “path” interference in low energy He+ + He collisions

Abstract Coulomb “path” interference results from the existence of two trajectories, indistinguishable with respect to laboratory energy and emission angle, along which ejected autoionizing electrons may be scattered by the attractive Coulomb potential of the slowly receding spectator ion. Experimental evidence for this new phenomenon exists in the uncharacterestically rapid angular dependence of the postcollision broadened lineshape of the He target 2s 2 1 S autoionizing state measured near 0° following 10 keV He + + He collisions. We present a semiclassical model for this effect in which we account for the path dependence of the amplitude of the ejected electron following decay of the autoionizing state. Calculated model lineshapes, which include contributions from adjacent overlapping resonances, are found to be in excellent agreement with the angular dependence observed in the data. Similar interference structure is observed in the calculated lineshape for a single isolated 2s 2 1 S resonance.

Collision experiments with highly ionized atoms

Low-energy inelastic collision processes involving highly ionized atoms have become the subject of a steadily growing number of experimental and theoretical investigations. The majority of these studies have focused on collisions which produce a net change in the charge of the ion. Summarized here are results of some recent investigations of multiply charged ion interactions with neutral atoms and with electrons conducted at Oak Ridge National Laboratory. Special emphasis is given to systematic studies of interaction mechanisms, and to two experiments which show evidence for the correlated motion of electrons during the collision.

Survey of experimental and theoretical electron-impact ionization cross sections for transition metal ions in low stages of ionization

Electron-ion crossed beams measurements and distorted-wave theory have been employed to make a study of electron-impact ionization for transition metal ions in low stages of ionization. The atomic ions Ti+, Ti/sup 2/+, Ti/sup 3/+, Fe+, Fe/sup 2/+, Fe/sup 3/+, Fe/sup 4/+, Ni+, Ni/sup 2/+, Ni/sup 3/+, Cu+, Cu/sup 2/+, and Cu/sup 3/+ are examined.

Electron impact ionization of multicharged ions at ORNL: 1980-1984

Absolute cross sections are presented in graphs and tables for single ionization of forty-one ions, multiple ionization of four ions, and for dissociation and ionization of two molecular ions by electron impact. This memo is the third in a series of manuscripts summarizing previously published as well as unpublished ionization cross section measurements at ORNL; contents of the two previous memos are also referenced in this work. All work tabulated in this memo involved ion beams generated in the ORNL-ECR ion source and utilized the ORNL electron-ion crossed beams apparatus. Target ions range from atomic number Z = 8 (oxygen) to Z = 92 (uranium) in initial charge states from +1 to +16. Electron impact energies typically range from threshold to 1500 eV.

Ionisation of H-, He- and Li-like 1 GeV Ni ions in solid carbon targets

Data for the electron loss from 1 GeV H-, He- and Li-like Ni ions incident on thin solid carbon targets have been obtained. The targets were sufficiently thin to achieve single-collision conditions and hence permit the determination of the ionisation cross sections. Despite the high velocity ( beta approximately 0.2) of the H-like Ni ions the collision regime is such that neither the Bohr theory based on an impact parameter formalism nor the Born approximation, even to second order, are appropriate for treating the ionisation process. The cross sections measured for electron loss were found to be significantly lower than these theoretical estimates. The single-electron ionisation cross sections for the Li-like Ni ions showed a marked increase over those for the H-like or He-like ions consistent with a strong electron binding energy dependence.