Kazuhiko Okuno

Charge Transfer of Ar2+ and Kr2+ in Their Own Gases Studied by the Beam Guide Technique

By an o cto p ole i on-beam g uide ( OPIG ) technique combined with a tandem mass spectrometer technique, one- and two-electron capture cross sections of Ar 2+ and Kr 2+ in their own gases have been measured in the wide collision energy range from 0.1 to 1000 eV (in center-of-mass systems). By changing electron impact energy to produce incident ions, contributions to cross sections from various ionic states in beams are examined. Two-electron capture cross sections are almost independent of ionic states, but one-electron capture cross sections depend strongly on ionic states. One-electron capture cross sections by \(^{3}\bm{P}\) state are determined at collision energies of 1.0, 10 and 100 eV. In this paper, it is also shown that this OPIG experiment is very useful for low energy collision experiments and spans well the energy gap in previous experiments.

Development of a Compact Electron Beam Ion Source Cooled with Liquid Nitrogen

A small-sized EBIS type ion source (mini-EBIS) for production of highly charged ions has been developed. The whole system, namely, the electron gun, ion drift tube, electron collector, ion extraction lens and liquid nitrogen reservoir containing solenoid coil is housed in a vacuum envelope, 150 mm in diameter and 500 mm in length. The idea of cooling the solenoid to 77 K has proved very effective to miniaturize the solenoid and its power supply. Moreover, the wall of the liquid nitrogen reservoir exhibits a cryogenic pumping function at the ionization region. In the DC ion extraction mode with an electron current of 15 mA at 2 keV, beam intensities obtained for C6+, N7+, O8+, Ne9+ and Ar16+ ions are at least 5×104, 3×104, 1×104, 5×103 and 3×103 counts per second, respectively.

Landau-Zener model calculations of one-electron capture from He atoms by highly stripped ions at low energies

Cross sections for single electron capture from He atom by highly stripped, C q + , N q + , O q + , F q + , Ne q + ( q =4–9) and Kr q + ( q =10–25) ions have been calculated using the multichannel Landau-Zener model. The collision energy is 600 eV/amu except for Kr q + , whose energy is q ×1 keV. The selective electron capture into a single or at most two n -shells is predicted for the cases of q ≤9. The n -distributions obtained by the present calculation are quite consistent with our earlier observation and the total cross sections agree reasonably well with the measured data in spite of the simple model. In the case of Kr q + , where q is larger than 10, more and more shells can be populated and the total cross sections increase monotonically with the increase of q .

Absolute Measurement of Total Ionization Cross Section of Mg by Electron Impact

Total ionization cross section of Mg by electron impact has been measured absolutely by the crossed beam technique. Intensity of neutral Mg beam is determined by the deposition method. Mg atoms deposited onto a beam collector are quantitatively analyzed by atomic absorption spectrophotometry. The absolute cross sections at 22.4 eV, 106 eV, 492 eV and 1000 eV are determined to be 9.1, 3.9, 1.7 and 1.0×10 -16 cm 2 , respectively. Systematic errors are estimated to be within -15% and +8%. Relative cross section is obtained as a function of electron energy from the threshold to 1130 eV. The results are compared with some experimental results and theoretical calculations by other workers.

Drift Tube Study of Symmetric Resonance Single- and Double-Charge Transfer in Kr++Kr, Xe++Xe, Kr+++Kr, and Xe+++Xe Systems

An injected-ion drift tube mass spectrometer is used to determine the cross sections of processes Kr + +Kr→Kr+Kr + , Xe + +Xe→Xe+Xe + , Kr ++ +Kr→Kr+Kr ++ , and Xe ++ +Xe→Xe+Xe ++ . The drift tube was operated with He buffer gas and cooled with liquid nitrogen so that the energy range studied was widened as from 10 meV to 10 eV. It was found that, at the lowest energy end, the energy dependence of cross section for single charge transfer deviates from that expected by linear trajectory model. For double charge transfer, the cross section below 1 eV almost coincide with the orbiting cross section with a charge transfer probability 1/2. Above 1 eV, the energy dependence of the cross section is like that for single charge transfer. Mobilities of Kr + , Xe + , Kr ++ , and Xe ++ in He at 296 K and 82 K are presented also.

Application of mini-EBIS to cross section measurements of single and double electron capture in low energy collisions of C4+, N4+ and O4+ with He

A small size electron beam ion source (mini-EBIS) cooled with liquid nitrogen has been developed for atomic collision research. An experimental technique using mini-EBIS in combination with an octupole ion beam guide (OPIG) has proved very useful for low energy collision experiments including highly charged ions. Single and double electron capture cross sections in collision systems of C4+He, N4+He and O4+ have been measured at low energies from 0.5 to 2000 eV in the center of mass system.

Desorption induced by electronic potential energy of multiply charged ions

Abstract Particle desorption is investigated in terms of bombardment of a GaAs surface by slow multiply charged Ar ions (charge state q ⩽ 9, kinetic energy E k ⩽ 3 keV). The desorption yield of Ga and As atoms as well as H + ions drastically increased with the charge state of the incident Ar ions, but was changed little by the kinetic energy of the Ar ions. These results demonstrate that desorption reactions at the surface are greatly enhanced by the potential energy of the incident ions. From an analysis of the potential energy dependence of the desorption yield based on the Coulomb explosion model, it is found that the lifetime of multiple holes created by the multiply charged Ar ions is longer than that of a single hole by 2 to 3 orders of magnitude.

A new apparatus for electron-ion coincidence studies

Design and operation of a new apparatus for electron–ion coincidence studies is described. For ionic fragmentation of inner‐shell excited molecules, the degree of decomposition of the molecule depends on where valence two holes are created by a subsequent Auger decay. Auger electron–photoion coincidence (AEPICO) measurements are indispensable for studying the ionic fragmentations of the core‐excited molecules, because these measurements can define the fragmentation products produced from a certain Auger final state. Experimental results for SiF4 are demonstrated as an example for the performance of the apparatus.

Measurement of Relative Population between B2+(2s) and B2+(2p) in Electron Capture Collision of B3+with He

One-electron capture processes into B 2+ (2s) and B 2+ (2p) have been investigated in B 3+ –He collision at low velocities (1.3-2.3×10 7 cm/sec) using a translation energy spectroscopy. Energy dependence of the relative population between B 2+ (2s) and B 2+ (2p) is obtained and compared with the theoretical result of Shipsey et al.

State-selective scattering angular dependent fragmentation of N2 by slow Kr8+ ion impact

Abstract We have newly developed a multiple coincidence method to study state-selective scattering angular resolved fragmentation of molecules caused by slow highly charged ion impact. The fragmentation of N 2 in double charge changing collisions of Kr 8+ at 19 eV/u has been investigated using the multiple coincidence technique. The energy gain distributions and scattering angle distributions of product Kr 6+ ions in coincidence with the double time-of-flight of fragment ions are obtained for fragmentation processes of N + +N + ions, N + +N 2+ ions and N 2+ +N 2+ ions, and the reaction energies of their processes are determined.