M Yoshino

A scaling law of cross sections for multiple electron transfer in slow collisions between highly charged ions and atoms

A simple scaling relation is derived for the partial and total multiple-electron capture cross sections in slow collisions of highly charged ions with atoms based on the extended classical over-barrier model. It is shown that the currently available experimental cross sections are reproduced quite satisfactorily by this relation.

Electron impact ionization of O+, S+ and S2+ ions

Absolute cross sections for electron impact single ionization of O + , S + and S 2+ ions have been measured at an electron impact energy range from below threshold to 1000 eV, using the crossed beam technique. The measured cross sections for O + ions are reproduced quite well with the semiempirical Lotz formula over the whole energy range investigated. The measured cross sections for S + and S 2+ ions show a more rapid rise from the threshold to their peak than those expected from the Lotz formula. For S 2+ ions, another small bump beginning at 120 eV is observed, where no level exists that may contribute to any direct or indirect ionization processes.

Single and double photoionisation of Ca atoms between 35 and 42 nm

Photoionisation of Ca atoms has been investigated by means of a time-of-flight mass spectrometer coupled with a source of monochromatised synchrotron radiation and an atomic Ca beam. Relative photoionisation cross sections (q+ for single photoionisation and q2+ for double photoionisation, as well as the ratio R=q2+/q+) have been measured in the wavelength range 35-42 nm with a 0.15 nm bandwidth. Comparison with the photoabsorption data of Mansfield and Newsom (1977) shows a good correspondence in the peak structure between the absorption resonance and the Ca2+ yield for proton energies above the lowest 3p ionisation limit. The variation of R with wavelength exhibits a step behaviour which correlates with some of the 3p ionisation limits.

Electron Impact Ionization of C + , N + and P + Ions

Absolute cross sections for electron impact ionization of C + , N + and P + ions have been measured for electron energies from threshold up to 1000 eV, using the crossed beam technique. The measured cross sections for both C + and N + ions are in good agreement with the semiempirical Lotz formula over the whole energy range investigated, and also with those previously reported except for near threshold. The results for P + ions show a more rapid rise from the threshold and larger values around the peak than those calculated with the Lotz formula.

Ionic fragmentation of SiH4 following the L-shell excitation

Ionic photofragmentation of SiH4 has been studied in the vicinity of the Si: L-edge using synchrotron radiation and time-of-flight mass spectrometry. Relative ionization efficiencies for more then 10 ionic fragment species and pair-ionization efficiencies for the pairs H+ + SiHn+ (n=0, 1 and 2) have been obtained as a function of the photon energy from 100 to 200 eV from the photoelectron-photion and the photoion-photoion coincidence measurements. Ionic dissociation of the continuum Si: 2p hole states may occur mostly via double ionization of the parent molecule giving rise to two types of dissociation channels; (type A) SiH4++ → H+ + H+ + neutrals and (type B) SiH4++ → H+ + Si+ (or SiH+) + neutrals. The average kinetic-energy release given to H+ is much higher in the dissociation channel B than in the dissociation channel A suggesting temporal existence of localized and delocalized valence-two-hole states.

Electron Inpact Single Ionization of Ne2+, Ar2+, Kr2+ and Xe2+ Ions

Absolute cross sections for electron impact single ionization of doubly charged rare gas ions, Ne 2+ , Ar 2+ , Kr 2+ and Xe 2+ , have been measured in the energy range from below threshold to 1000 eV. The measurements were performed with crossed electron and ion beam technique. The measured cross sections for Ne 2+ ions are found to be in good agreement with the semiempirical Lotz formula for direct ionization. For Ar 2+ ions is found a small discrepancy between the observed cross section and the formula at lower energies. For Kr 2+ and Xe 2+ ions the measured cross sections exhibit complicated structures from threshold to medium energy and are significantly larger than estimates for the direct ionization. These enhancements and complex structures are believed to be indirect ionization processes, such as excitation-autoionization.

Absorption Cross Sections and Photoionization Efficiencies of Benzene and Styrene Vapor in the Vacuum Ultraviolet

Absorption cross sections and photoionization efficiencies of benzene and styrene vapor have been measured in the wavelength regions of 600–2200 A and of 600–1000 A, respectively. Strong absorption peaks ascribed to the π-electron transition 1 A 1g → 1 E 1u have been observed at 1790 A for benzene and at 1960 A for styrene. Corresponding oscillator strengths are 0.91 and 0.62, respectively. A strong and broad continuum with its maximum at about 700 A has been observed for both benzene and styrene; cross sections around the maximum are 140 and 180 in unit of 10 -18 cm 2 , respectively. Energy-loss spectra for styrene vapor have been deduced from the present results and compared with previous data on the solid polystyrene. It is pointed out on the basis of the above results, that the transitions at the energy-loss of 6.5–7 eV and of 20 eV can be interpreted as due to a molecular excitation and a photoionization process, respectively, and that the previous assignments as due to collective excitations are unn...

Target dependence of multi-electron processes in Iq+ (q=10, 15)+rare gas (Ne, Ar, Kr and Xe) collisions

We have determined experimentally the absolute cross sections for i-electron capture (to projectile) and j-electron removal (from target) ( sigma q,q-ij), total electron capture ( sigma q= Sigma i sigma q,q-i), j-electron removal ( sigma qj= Sigma i sigma q,q-ij) and i-electron capture ( sigma q,q-i= Sigma j sigma q,q-ij) for the processes: Iq+(q=10 or 15)+B to I(q-i)++Bj++(j-i)e (B identical to Ne, Ar, Kr and Xe) at collision energy of 1.5q keV. Charge-state distributions of the scattered ions were measured in coincidence with the recoil ions. The absolute electron-capture cross sections were measured by the initial growth-rate method. The experimental results for sigma q and sigma qj were compared with the predictions of the extended classical over-barrier model (ECBM). The branching ratios of the multiply-excited ions produced by multi-electron transfer have also been determined.

4d-shell photoionization of Xe, Cs, Ba, Sm, Eu and Yb atoms studied by photoion-yield spectra

A comparative study of multiple photoionization in the 4d ionization region (78-270eV) of M = Xe, Cs, Ba, Sm, Eu and Yb atoms is reported. Partial photion-yield spectra for Mn+ (n = 1-4) ions have been measured by using synchrotron radiation as a light source. Main products in Xe, Cs and Ba are Mn2+ and M3+ ions due to the creation of a 4d vacancy. In Sm and Eu, a large fraction of M+ ions are populated via the 4d-4f resonant excitation and subsequent autoionization to the 4f ionization continuum, which is squeezing the population of multiply-charged ions to about 50%. In Yb, a large amount of M+ ions are also populated, but are due largely to the direct 4f ionization. In all of the atoms studied, an appreciable or considerable amount of M4+ ions are observed, indicating the existence of photoelectron and/or Auger shake-off processes.

A two-dimensional position-sensitive anode for microchannel plates based on the “MBWC” technique

Abstract The modified backgammon method with weighted coupling capacitors (MBWC) has been applied to a tandemmicrochannel-plate charged-particle detector for two-dimensional position encoding. After some optimizing procedure a position resolution better than 40 μm (FWHM) is obtained for an avalanche size of ∼ 1 × 10 7 electrons. Individual microchannels with 15 μm spacing are clearly resolved at the avalanche size of ∼ 4 × 10 7 electrons. Acceptable image linearity over the whole MCP sensitive area of 20 mm ace gf is obtained.