Relativistic Distorted-Wave Calculations of Electron Impact Excitation Cross Sections of Be-Like C2＋ Ions

A fully relativistic distorted-wave program is developed based on the Grasp92 and Ratip packages to calculate electron impact excitation （EIE） cross sections. As a first application of the program, the EIE cross sections of Be-like C^α＋ ions from the metastable 1s^22s2p^3 p to 1s^22p^2 ^3 p excitation and the inner-shell excitations are calculated systematically. Meanwhile, the correlation effects of target states are discussed. It is found that the correlation effects play an important role in the low energy EIE cross sections. An excellent agreement is found when the results are compared with previous calculations and recent measurements.     

Relativistic Configuration Interaction Treatment of Generalized Oscillator Strength for Krypton

A fully relativistic configuration interaction method is developed to investigate the transition energies and general oscillator strengths of the lower lying states of krypton, for both optically allowed and optically forbidden transitions. The calculated results are in agreement with the recent experimental measurements. The calculated transition energies for the 5s and 5s＇ transitions are 9.970 and 10. 717eV, which agree with the experimental data of 10.033 and 10.643 eV. The calculated oscillator strengths are 0.211 and 0. 170, comparable with the experimental results 0.214（±0.012） and 0.194 （±0.012）, respectively. The momentum transfer positions （K^2 in a.u.） of the minimum and maximum GOSs in the 4s^24p^6 → 4s^24p^5 （5s ＋ 5s＇） transitions are 1.105 and 2.225, comparable with the measurements results 1.24 and 2.97 [Phys. Rev. A 67 （2003） 062708].     

Dielectronic Recombination of Sn^10＋ Ions and Related Satellite Spectra

Based on the multi-configuration Dirac-Fock method, theoretical calculations are carried out for the dielectronic recombination （DR） rate coefficients and the collision excitation rate coefficients of Sn^10＋ ions. It is found that the total DR rate coefficient has its maximum value between 10eV and 100eV and is greater than either the radiative recombination or three-body recombination rate coefficients （the number of free electrons per unit is 10^21 cm^3） for the ease of Te 〉 1 eV. Therefore, DR can strongly influence the ionization balance of laser produced multi-charged tin ions. The related dieleetronie satellite cannot be ignored at low temperature Te 〈 5 eV.     

Theoretical Study on Inner Shell Electron Impact Excitation of Lithium

Cross sections for electron impact excitation of lithium from the ground state 1s^22s to the excited states 1s2s^2, 1s2p^2, 1s2snp （n = 2-5）, 1s2sns （n = 3 5）, 1s2pns （n = 3-5）, and 1s2pnp （n = 3-5） are calculated by using a full relativistic distorted wave method. The latest experimental electron energy loss spectra for inner-shell electron excitations of lithium at a given incident electron energy of 2500 eV [Chin. Phys. Lett. 25 （2008）3649] have been reproduced by the present theoretical investigation excellently. At the same time, the structures of electron energy loss spectra of lithium at low incident electron energy are also predicted theoretically, it is found that the electron energy loss spectra in the energy region of 55-57eV show two-peak structures.     

Polarization of Radiation Emitted after Electron Impact Excitation

A programme is developed to calculate the polarizations of the radiation emitted after electron impact excitation. The fully relativistic distorted-wave method is used in cross-section calculations. The programme is applied to He- and Li-like ions. The calculated values of line polarization are compared with other theoretical results and experimental values. For He-like U, at lower incident energy, the present polarization agrees with the other theoretical ones within 1%, while at higher energy, the differences increase up to about 10%. For He-like Fe and Ti, the present results of polarization degree for most of the lines agree with the experimental data within the experimental error bars. For the Li-like Ti line q （ls2s2p^2p3/2 to ls^22s）, the present value of the polarization agree excellently with another theoretical one, and both the values are consistent with the measured data within the experimental error bar.     

Excitation and photoionization processes involving the bound ns electrons

We have considered the processes of excitation and ionization of light multicharged ions by impact of high-energy particles, which proceed with participation of the ns electrons. The screening corrections to the energy levels and photoionization cross sections are evaluated analytically within the framework of the non-relativistic perturbation theory with respect to the electron-electron interaction. The universal scalings for the excitation and ionization cross sections are studied for arbitrary principal quantum numbers n.     

Relativistic Multichannel Treatment of Ionic Rydberg States of Lanthanum

Ionic Rydberg energy levels of lanthanum are calculated from first principles by relativistic multichannel theory within the framework of multichannel quantum defect theory. The present calculated results are in better agreement with the experimental measurements than the previous calculations [J. Phys. B 34 （2001）369] due to the consideration of dynamical polarizations. Moreover, in the experimental spectra achieved by a five-laser resonance excitation via the intermediate state 5d6d^3 F2, a series of weak ionic Rydberg states and some of perturbing states are found and assigned in this work.     

Ionisation of phosphorus, arsenic, antimony, and bismuth by electron impact

Total ionization cross sections of neutral phosphorus, arsenic, antimony, and bismuth atoms by electron impact are reported and compared to the only available experimental results by Freund et al. [Phys. Rev. A 41, 3575 (1990)]. These calculations take into account the possibilities that some target atoms used in the experiments were in metastable states close to the ground state, the excitation-autoionization of nsnp⁴ excited states may be substantial, and the ions produced in experiments may be in excited, low-lying metastable states. The cross sections for direct ionization calculations are based on the BEB model by Kim and Rudd [Phys. Rev. A 50, 3954 (1994)]. Plane-wave Born cross sections scaled by the method developed by Kim [Phys. Rev. A 64, 3954 032713 (2001)] are used to determine the contributions from excitation-autoionization. The combination of the BEB model and the scaled Born cross sections is in agreement with the experimental data by Freund et al. These theoretical data are useful to experimentalists and can be used to complete data tables needed for plasma or astrophysical studies.     

Importance of Relativistic Effects for Intermediate-Z Elements： Photoionization Process of Excited Na

Using a modified R-matrix code, the fine-structure-resolved partial photoionization cross sections of excited Na （Z = 11） are calculated within the Breit-Pauli approximation. Our calculated energy levels of Na＋ and Na are in good agreement with the experimental values within 1% and the branching ratios of the J-resolved partial cross sections are consistent with the recent measurements within the experimental uncertainties. The agreements are impossible to be obtained without adequately taking into account the relativistic effects and the electron correlations together. Therefore, even for the intermediate-Z elements （e.g. Na with Z = 11）, the relativistic effects （mainly the spin-orbit interactions） should not be neglected.     

Resonance Energies,Absorption Oscillator Strengths and Ionization Potentials for the Element Hassium （Z = 108）

On the basis of successfully predicting low-lying energy levels for the element fermium （Z = 100）, we calculate the resonance energies, absorption oscillator strengths and the first ionization potential of the element hassium （Z = 108） by taking important relativistic and improved electron correlation effects into account using the multiconfiguration Dirac Fock method. These calculations are carried out with the aim of assisting experimental investigations of hassium.     

Theoretical Investigation of Decay Process in a Doubly Excited 2s^2 ^1S0 State of He-Like Ions

In the framework of multi-configuration Dirac-Fock theory, a detailed calculation is performed for the decay rates and the energies of the doubly excited 2s^2 ^1So state of He-like ions, of which atomic number Z ranges from 6 to 92. The 2s^2 ^1So - ls ^2S1/2 Auger decay is predominant at low Z regime, whereas the 2s^2 ^1So - 1s2p ^1,3P1 two-electron one-photon transitions become quite important in moderate and high Z regimes. For heavy ions with Z ≥ 72, the contribution of 2s^2 ^1So - 1s2s ^3S1 M1 transition is significant. The Breit interaction considerably enhances the 2s^2 ^1So - 1s ^2S1/2 Auger rate at high Z regime.     

Calculation of dielectronic recombination cross sections and rate coefficients for heliumlike carbon

A simplified relativistic configuration interaction method is used to calculate the dielectronic recombination cross sections and rate coefficients for heliumlike carbon. In this method, the infinite resonant doubly excited states can be treated conveniently in the frame of Quantum Defect Theory. Our calculated cross sections are in agreements with the experimental measurements except for the 1s2lnl'(n=6,7) resonances. The total energy-integrated cross sections and rate coefficients over all dielectronic resonances are in agreements with the experimental measurements within percent. Received: 7 July 1997 / Revised: 7 October 1997 / Accepted: 8 December 1997     

Electron collisional excitation of argon-like Ni XI using the Breit-Pauli R-matrix method

Electron excitation collision strengths for the transitions from the ground state to the fine-structure levels of the 3s²3p⁵3d and 3s²3p⁶3d configurations in Ni XI are calculated using the Breit-Pauli R-matrix method. Configuration interaction wavefunctions have been used to represent the target states. The relativistic effects are incorporated in the Breit-Pauli approximation by including one-body mass correction, Darwin, and spin-orbit interaction terms in the scattering equations. Collision strengths are tabulated at selected energies in the range 10 to 75 Rydberg. Effective collision strengths are determined by integrating collision strengths by assuming a Maxwellian distribution of electron energies. The effective collision strengths are listed over a wide temperature range (2×10⁴-1×10⁷ K) applicable to astrophysical plasmas. Our results are the only collision strengths and effective collision strengths available for this ion. We believe that the data calculated in this work will be useful in solar, astrophysical and laser applications.     

Calculation of the contributions from high-n dielectronic satellites to the resonance line in helium-like iron

A simplified relativistic configuration interaction method is used to study the dielectronic satellite transition processes. In this method, the infinite resonant doubly excited states can be calculated, and furthermore, the whole high-n dielectronic satellite transition processes can be treated conveniently by interpolation (rather than extrapolation) in the frame of Quantum Defect Theory. As an example, we calculate the contributions from high-n dielectronic satellites to the resonance line in helium-like iron, and the results are in good agreement with the experimental measurements. Received: 16 April 1998 / Revised: 8 September 1998 / Accepted: 14 September 1998     

Optically Forbidden Excitations of 2s Electron of Neon Studied by Fast Electron Impact

The electron energy loss spectrum in the energy region of 42-48.5 eV of neon is measured with an angle-resolved fast-electron energy-loss spectrometer at an incident electron energy of 2500eV. Besides the dipole-allowed autoionization transitions of 2s^-1ap （n -= 3, 4） and 2p^-23s3p, the dipole-forbidden ones of 2s^-1ns （n = 3 - 6） and 2s^-13d are observed. The line profile parameters, i.e. Er, F and q for these transitions, are determined, and the momentum transfer dependence behaviour is discussed.     

Inner Shell Excitations of Lithium Studied by Fast Electron Impact

Electron energy loss spectra for the inner shell excitations of atomic lithium are measured at an incident electron energy of 2500eV and scattering angles of 0^o, 2^o, 4^o and 6^o. Two optically forbidden transitions of （ls2s^2）^2S and （ ls2s ^3 S）3s^2 S are observed. The generalized oscillator strength ratios for ls（2s2p^3 P）2 P^0 to 1s（ 2s2p^1 P）2 P^0 were determined, and they are independent of the momentum transfer.     

Theoretical study of the KLL dielectronic recombination for highly charged iodine ions

With a developed program for calculation of dielectronic recombination (DR) process, which is based on multi-configuration Dirac-Fock (MCDF) method, the KLL DR processes of the highly charged helium-like to carbon-like iodine ions have been studied systematically. The contributions to doubly excited states from quantum electrodynamic (QED) and Breit effects have been discussed. The KLL DR resonant energies and corresponding resonant strengths have been calculated. The behavior of KLL resonant strengths with increasing Z are analyzed for He-like ions in particular. The theoretical DR spectra for each highly charged ion species are obtained in the KLL region. Comparison has been made between the present calculations and the latest experiments in Tokyo-EBIT.     

Double ionization of helium with classical ensemble simulations

The classical ensemble method is used to study the dynamic process of the 1D helium interacting with intense laser pulses. Probabilities of double-ionization of helium in intense laser fields are calculated by the symplectic method. The wavelength dependence of double ionization in He is investigated. The non-sequential double ionization (NSDI) is observed in classical simulations at the laser wavelength of 532 nm, 780 nm and 1024 nm, respectively, while the sequential double ionization (SDI) is the dominant process at the laser wavelength of 248 nm. The pulse duration dependence on NSDI is also studied and the result is in agreement with the corresponding experimental results qualitatively.     

Ionization of K-shell electrons by electron impact

We have investigated the universal scaling behavior for cross sections of the single K-shell ionization by electron impact. The calculations are performed within the framework of non-relativistic perturbation theory, taking into account the one-photon exchange diagrams. Special emphasis is laid on the near-threshold energy domain. The results obtained are applicable for wide family of atomic targets with moderate values of the nuclear charge Z.     

Ionization of K-shell electrons by positron impact

We have investigated the universal scaling behavior for cross sections of the single K-shell ionization by positron impact. The calculations are performed within the framework of non-relativistic perturbation theory, taking into account the one-photon exchange. Special emphasis is laid on the near-threshold energy domain. The results obtained are applicable for wide family of atomic targets.