Relativistic Distorted-wave Method Research Articles

Excitation of the D states of cadmium and barium by electron impact

The authors have applied their relativistic distorted-wave method to the excitation of the 1D2 and 3D1,2,3 states of cadmium and barium from their 1S0 ground states. Comparisons are made with experimentally measured differential cross sections for the excitation of the singlet states for impact energies in the range 20 to 100 eV. The authors also present a complete set of spin-polarization parameters at 40 eV for both atoms.

Relativistic distorted-wave calculation of electron excitation of heavy noble gases

The authors have applied our completely relativistic distorted-wave method to the electron impact excitation of the heavy noble gases Ar, Kr and Xe. Results for spin polarization parameters, electron-photon coherence parameters as well as differential cross sections are presented and compared with previous semi-relativistic calculations. Overall good agreement with experimental measurements of the differential cross section and the coherence parameters is obtained. Notably different results for spin polarization parameters are predicted compared with previous semi-relativistic calculations.

Relativistic distorted-wave calculation of electron excitation of cadmium

The authors have applied their completely relativistic distorted-wave method to the electron impact excitation of the 5 1P1 and 5 3P0.1.2 states of cadmium. Results for a complete set of spin polarization as well as orientation and alignment parameters are presented and compared with recent semi-relativistic calculations. Good agreement with recent experimental measurements of the differential cross section is obtained.

Rapid relativistic distorted-wave approach for calculating cross sections for ionization of highly charged ions.

The rapid relativistic distorted-wave method of Zhang, Sampson, and Mohanty [Phys. Rev. A 40, 616 (1989)] for excitation, which uses the atomic-structure data of Sampson et al. [Phys. Rev. A 40, 604 (1989)], has been extended to ionization. In this approach the same Dirac-Fock-Slater potential evaluated using a single mean configuration is used in calculating the orbitals of all electrons bound and free. Values for the cross sections Q for ionization of various ions have been calculated, and generally good agreement is obtained with other recent relativistic calculations. When results are expressed in terms of the reduced ionization cross section ${\mathit{Q}}_{\mathit{R}}$, which is proportional to ${\mathit{I}}^{2}$Q, they are close to the nonrelativistic Coulomb-Born-exchange values of Moores, Golden, and Sampson [J. Phys. B 13, 385 (1980)] for hydrogenic ions except for high Z and/or high energies. This suggests that fits of the ${\mathit{Q}}_{\mathit{R}}$ to simple functions of the impact electron energy in threshold units with coefficients that are quite slowly varying functions of an effective Z can probably be made. This would be convenient for plasma-modeling applications.

Effects of autoionizing resonances on electron-impact excitation rates for transitions among n=3 levels in neonlike selenium.

Direct and resonance excitation rate coefficients have been calculated for transitions between states with principal quantum number {ital n}=3 in Ne-like selenium. A relativistic distorted-wave method was used to compute the direct excitation rate coefficients and the resonance excitation rate coefficients were obtained using a multiconfiguration Dirac-Fock method. The effect of autoionizing resonances has been found to be significant for most transitions, especially at low temperatures. The resonances enhance the rate coefficients for some electric-dipole-allowed transitions by as much as a factor of 2. For strongly forbidden transitions, resonances can increase the rate coefficients by more than an order of magnitude.

Electron-impact ionization of highly charged hydrogenic atomic ions.

Electron-impact-ionization cross sections are calculated for hydrogenic ions with nuclear charge between 26 and 92, for incident electron energies up to 8 times the ionization energy, by a relativistic distorted-wave method. The results demonstrate the increasing importance of relativistic effects with Z and with incident electron energy, particularly for 1s ionization. The effects of including magnetic and retardation interactions as Z increases are also studied. Results are compared with scaled K-shell ionization measurements for $^{47}\mathrm{Ag}$ and $^{79}\mathrm{Au}$.

Excitation-autoionization processes in electron-impact ionization of Au68+

Relativistic electron-impact ionization cross sections have been calculated for Au{sup 68+}. Direct ionization cross sections were computed using a relativistic distorted-wave method. Relativistic distorted-wave electron collisional excitation cross sections and detailed relativistic radiative and Auger rates were calculated in order to determine the contribution of excitation-autoionization processes. Because radiative channels are the predominant decay modes for highly charged heavy ions, the effects of excitation-autoionization processes were expected to be small for Au{sup 68+}. However, we found that these processes enhance the direct ionization cross sections by a factor of 4. This enhancement may be observed in experiments on the electron-beam ion trap in the near future.

Fully relativistic and quasirelativistic distorted-wave methods for calculating collision strengths for highly charged ions.

A rapid fully relativistic distorted-wave method for calculating collision strengths for highly charged ions is described. A more rapid quasirelativistic approximation in which the average over j value -1 is used for the relativistic quantum number \ensuremath{\kappa} for the free electrons is also discussed. Very rapid, but accurate, procedures for obtaining results for a given class of transitions for a large portion of an isoelectronic sequence by using fits to Z after making detailed calculations for only a few values of Z are described. Results by the present methods are compared with more elaborate relativistic distorted-wave calculations by other workers, principally for neonlike and nickel-like ions, but also comparisons for He-like, Li-like, and Na-like ions are discussed. In addition, comparisons with a few experimental results for neonlike barium could be made. Generally very good agreement is obtained with all these data.