Electron impact ionization of Zn+ and Ga+

We have investigated the contribution of excitation-autoionization to the electron impact ionization of Zn⁺ and Ga⁺ using the binary encounter approximation. Hartree-Fock velocity distributions for the bound electrons have been used throughout the calculations of direct and indirect ionization cross-sections. The calculated cross-sections are in good agreement with recent experiments. We have also compared our results with other theoretical calculations.     

Electron impact double ionization of Fe+ and Fe3+

Electron impact double ionization cross-sections for Fe⁺ and Fe³⁺ have been calculated in the modified binary encounter model incorporating the effects of the Coulombic field of the target on the incident electron. Accurate expression of cross-section for energy transfer ΔE given by Vriens and Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. The present results show satisfactory agreement with experimental observations. It is concluded that the discrepancy in the high energy region observed in the present calculations may be attributed to non-inclusion of indirect ionization processes arising from the L-shell.     

钙、锶、钡和汞离子激光中的共振辐射俘获效应

根据Holstein的共振辐射俘获理论，讨论了气体温度和辐射俘获下能级粒子数密度对辐射俘获上能级有效辐射寿命的影响，显示辐射俘获下能级粒子数密度是辐射俘获效应中的主导因素.计算了钙，锶，钡和汞四种离子七条共振-亚稳能级跃迁激光在不同电离率下产生共振辐射俘获效应的阈值条件，发现当电离率为5%时这类激光的出光温度与共振辐射俘获的阈值温度相一致，这与实验得出的电离率为3%—5%相符合.表明达到共振辐射俘获阈值条件是该类激光实现粒子数反转的重要因素.     

Proton and α-particle impactM-shell ionization of atoms in binary encounter approximation

M-shell ionization cross sections for atoms due to the impact of proton and α-particles have been calculated in the binary encounter approximation. The effects of Coulomb deflection of the incident projectile and increase in binding of the target electron have been investigated. Roothan-Hartree-Fock velocity distribution for the target electrons has been used in the present work. The calculated cross-sections have been compared with experimental results and other theoretical calculations wherever available. The present calculations give a good account of experimental observations.     

Double ionization of Sc<Superscript>+</Superscript>ions by electron impact

Electron impact double ionization cross-sections of Sc⁺ions have been calculated in the binary encounter approximation (BEA). Accurate expression of σ_ΔE(cross-section for energy transfer ΔE) and Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. Direct double ionization from ejection of 3d and 4s electrons has been investigated in the modified double binary encounter model incorporating the focusing action of the target ion on the incident electron. The identification of the 3p shell whose ionization provides a major contribution to double ionization through ionization-autoionization is an interesting aspect of the present investigation. The theoretical results show satisfactory agreement with the experimental observations.     

Electron impact single and double ionization of halogens

The binary encounter approximation has been used for calculations of electron impact single ionization cross-sections for F, Cl, Br and I and double ionization cross-sections for Br and I. Contributions of ionization from inner shells have also been included in the calculations. Hartree-Fock momentum distribution has been used for the bound electron as far as possible. The results have been found to be in satisfactory agreement with experimental observations.     

Electron impact ionization cross-section of C2, C3, Si2, Si3, SiC,SiC2 and Si2C

Total ionization cross-sections for C₂, C₃, Si₂, Si₃, SiC, SiC₂ and Si₂C molecules have been calculated by electron impact. Spherical complex optical potential formalism has been employed for obtaining the inelastic cross-sections for these molecules. Then by applying complex scattering potential-ionization contribution method, total ionization cross-sections are derived. These cross-sections are calculated in the energy range from ionization threshold to 2?keV. There are no measurements available in the literature to the best of our knowledge with which our results can be compared. The results show a linear relationship between maximum ionization cross-section and square root of the ratio of polarizability to ionization potential, depending on its atomicity. This gives a confirmation for the consistency of the data reported here. Present work is a maiden attempt to find electron impact ionization cross-section for these molecules, except for C₂ and C₃.     

Electron impact single ionization of mono- and di-positive ions

The electron impact ionization cross-sections of mono- and di-positive ionic targets are calculated using a second version of the modified binary-encounter-dipole (MBED) model, previously reported [M A Uddinet al, J. Phys. B37, 1909 (2004)]. The present version differs from the previous one in the scale factor of the Burgess denominator and is applicable to targets with chargesq = 1 and 2. The MBED in the present form is found to work well for 11 ionic targets ranging from Be⁺ to K⁺ and complements its previous version valid for targets withq s> 2     

Electron impact single and double ionization of magnesium

Electron impact single and double ionization cross-sections for magnesium have been calculated in the binary encounter model using accurate expression for (cross-section for energy transfer ΔE) as given by Vriens. Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. In case of double ionization contributions of inner shell ionization and Auger emission have been included in the present work. The results obtained in case of single ionization are excellent and at the same time the double ionization cross-sections show reasonably good agreement with the recent experimental observations. Substantiation of the viewpoint of Peach, and Boivin and Srivastava that a vacancy in the 2p shell of magnesium leads to double ionization is a remarkable feature of the present investigation. Received 9 October 2001 / Received in final form 8 January 2002 Published online 28 June 2002     

Collision-energy-resolved Penning ionization electron spectroscopy of toluene and chlorotoluenes

Stereodynamics in ionization of toluene and o-, p-chlorotoluenes by collision with He^*(2³S) metastable atoms were investigated by two-dimensional collision-energy/electron-energy-resolved Penning ionization electron spectroscopy. Anisotropic interactions around the molecule were studied by the collision energy dependence of partial ionization cross-sections (CEDPICS) as well as model potential calculations, and shielding effect by the methyl group was observed in CEDPICS for ionization from Cl lone-pair orbitals of o- chlorotoluene. Attractive interaction with He^*(2³S) around the π orbital region was found to be larger for toluene rather than o-, p- chlorotoluenes. Exterior electron density (EED) calculation of partial ionization cross-sections in Penning ionization and negative CEDPICS for ionization band observed in ca. 4 eV in electron energy indicated that π^-2π⁺¹ shake-up state was observed in Penning ionization electron spectroscopy of toluene.     

H<Superscript>+</Superscript><Emphasis Type="Bold">and He</Emphasis><Superscript>2+</Superscript> impact single and double ionization of lead

H⁺ and He²⁺ impact single and double ionization cross sections of ground state lead atoms have been calculated in the binary encounter approximation. Calculations of direct double ionization cross sections have been performed in the modified double binary encounter model. The accurate expressions of σ_ΔE (cross-section for energy transfer ΔE) and Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. Contributions to double ionization from Auger effect following ionization of inner shells have been considered in the present work. Our H⁺ impact single and double ionization cross sections are in good agreement with the experimental observations. In calculations of He²⁺ impact cross sections, the present theoretical approach shows limited success in the experimentally investigated region (50–350 keV amu^-1).     

Photoionization cross-section measurements from the 2p, 3d and 3s excited states of lithium

The photoionization cross-sections from the 2p²P_{1/2, 3/2}, 3d²D_{3/2, 5/2} and 3s²S_1/2 excited states of lithium have been measured at different ionizing laser wavelengths, above the first ionization threshold. The experiments are performed by using a thermionic diode working in the space charge limited mode and the cross-sections are measured by employing the saturation technique. By changing the ionization photon energy, a smooth frequency dependence of the cross-sections has been observed for the 2p and 3d states. The cross-section from the 3s excited state has been measured at a single photon energy. The measured values of the photoionization cross are compared with the available data.     

Electron impact ionization of Ba,Ba+ and Ba2+

The binary encounter approximation has been used to investigate the effect of charge state of the target atom (ion) on the electron impact excitation autoionization cross-sections. Roothan-Hartree-Fock (RHF) velocity distribution for the bound electrons has been used through-out the calculations. The present results give a good account of the experimental observations.     

Two-dimensional Penning ionization electron spectroscopic study on outer characteristics of molecules

Collision-energy/electron-energy-resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES) has been used to study outer characteristics of molecules. Anisotropic potential energy surfaces for collisional ionization of molecules with a metastable helium atom He*(2³S) have been determined starting from ab initio model potentials via optimization based on trajectory calculations. Since ionization widths in the theoretical model of Penning ionization are functionals of target molecular orbitals, outer electron distributions of molecular orbitals can be determined via optimization procedures of calculated ionization cross-sections by trajectory calculations with respect to observed 2D-PIES data.     

Alpha particle and deuteron impactL-shell ionization of Ar,Cu, Ge,Br, Zr and Ag

Alpha particle and deuteron impactL-subshell ionization cross-sections of Ar, Cu, Ge, Br, Zr and Ag have been computed using Vriens’ expressions for ionization cross-section of atoms due to impact of heavy charged particles. The effects of Coulomb deflection of the projectile and increase in binding of the target electron in the presence of projectile have been incorporated. Hartree-Fock velocity distributions for the target electrons have been used in the present calculations. The simple binary encounter approximation model is found to give results which are in satisfactory agreement with those obtained from experiments and from other theories.     

Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Si q+-Ar collisions

A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Si ^q+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q ^1.7/E _p ^0.5 , where E _p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j ² upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σ _qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.     

Precise - and -factor measurements of Ba+ isotopes

Laser-microwave double and triple resonance experiments were performed on clouds of Ba⁺ ions confined in a Penning ion trap to induce and detect electronic and nuclear spin flip transitions. Collisions with buffer gas molecules in the trap was used to reduce the lifetime of a long lived metastable state of the ions, in which population trapping might occur, and to cool the ions to the ambient temperature. Loss of ions from the trap by collisions were prevented by coupling the magnetron and reduced cyclotron motions by an additional r.f. field at the sum frequency of the two motions. Electronic Zeeman transitions in ¹³⁸Ba⁺ and ¹³⁵Ba⁺ were observed at a full width of about 3 kHz at a transition frequency of 80 GHz. The uncertainty of the line center was . From the magnetic field calibration by the cyclotron resonance of electrons stored in the same trap the g_J-factor for both isotopes could be determined to . From radiofrequency induced transitions of ¹³⁵Ba⁺ the nuclear g-factor could be determined . Both measurements improve earlier results by about one order of magnitude. Received: 9 July 1998 / Accepted: 14 July 1998     

Diode laser spectrometer at 493 nm for single trapped Ba+ ions

+ ions. Frequency doubling of a 100 mW diode laser at 986 nm results in up to 60 mW output power at 493 nm in a bandwidth of less than 60 kHz with respect to the cavity used for locking. Reference frequencies of 18 spectral lines of Te₂ near the 493 nm resonance of Ba⁺ have been measured using modulation transfer spectroscopy. The fluorescence excitation spectrum of a single Ba⁺ ion, measured with this laser, exhibits well-resolved dark resonances, which confirms the versatility of the system for quantum optical experiments. Received: 12 June 1998     

Ionization and excitation of some atomic targets and metal oxides by electron impact

We have calculated total inelastic and total ionization cross-sections for collisions of electrons on atomic targets oxygen (O), aluminium (Al) and copper (Cu) and metal oxides AlO and Al₂O, at impact energies from near excitation threshold to 2000 eV. A complex (optical) energy-dependent interaction potential is used to derive total inelastic cross-sections resulting from ionization as well as excitation processes. The inelastic cross-sections are bifurcated into discrete and continuum contributions and total ionization cross-sections have been deduced therefrom. Our calculation also provides information, hitherto sparse, on the excitation processes in the atomic targets O, Al, Cu and metal oxides AlO, Al₂O. Adequate comparisons are made with other theoretical and experimental data.     

61Cu(61Ni) and 133Ba(133Cs) Mössbauer emission spectroscopy of Tl2Ba2Ca n−1CunO2n+4

The parameters of the electric-field gradient tensor at copper and barium sites in the Tl₂Ba₂Ca _n?1Cu_nO_2n+4 (n=1,2,3) lattice have been determined by ⁶¹Cu(⁶¹Ni) and ¹³³Ba(¹³³Cs) Mössbauer emission spectroscopy, and calculated in the point-charge approximation. The calculated parameters can be reconciled with experiment if one assumes that the holes produced as the valence state of a part of thallium atoms is lowered are localized predominantly on the oxygen sublattice lying in the same plane with copper atoms [in the Cu(2) plane in the Tl₂Ba₂Ca₂Cu₃O₁₀ lattice]. ¹³³Ba(¹³³Cs) Mössbauer emission spectroscopy data agree qualitatively with the proposed models of charge distribution in the Tl₂Ba₂Ca _n?1Cu_nO_2n+4 lattices.