Unitarized Distorted-wave Approximation Research Articles

Electron-impact excitation cross sections for Ar and Ar[formula omitted] by unitarized distorted-wave approximation

Unitarization for a relativistic distorted-wave approximation has been made by using two types of scattering matrix for reactance matrix and the electron-impact excitation cross sections for Ar and Ar+ are calculated by the unitarized relativistic distorted-wave method. The unitarization by using the scattering matrix obtained from diagonalization of the reactance matrix significantly reduces the cross sections rather than by using the scattering matrix given from inversion of matrix related to the reactance matrix which brings out better agreement with other more sophisticated R-matrix prediction and experiments at intermediate electron energies for Ar. The cross sections for Ar+ by the effective unitarization are smaller than those by available other prediction using perturbative relativistic distorted-wave approach.

Classical model for charge transfer and ionization in collisions of A q+ ( [formula omitted]) with ground-state hydrogen atom

We present both ionization and charge-transfer cross sections for A q + ( q = 1 – 6 ) + H ( 1 s ) collisions in the impact-energy range from 1 to 1000 keV/u. In calculations, the spatial distribution of the target electron represented by the simple wave function, the impact-parameter dependences of charge-transfer as well as ionization probabilities are derived based on Bohr–Lindhard model. The results show a good agreement with the available experimental data and with the other theoretical calculations based on the unitarized-distorted-wave approximation (UDWA) [H. Ryufuku, Phys. Rev. A 25 (1982) 720; H. Ryufuku, T. Watanabe, Phys. Rev. A 19 (1979) 1538] or the atomic-orbital close-coupling method (AOCC) [N. Toshima, Phys. Rev. A 50 (1994) 3940].

Modified over-barrier model for ionization cross sections of atomic hydrogen by multiply charged ions

The impact ionization of atomic hydrogen in collisions with H +, He 2+, Li 2 , 3 + , C 2 , 3 , 4 , 5 , 6 + , N 2 , 3 , 4 , 5 + , O 2 , 3 , 4 , 5 , 6 + , and Ar 3 , 4 , 5 , 6 + ions has been studied by the modified over-barrier model at low-to-intermediate velocities. Compared with the calculated results of the classical trajectory Monte Carlo (CTMC) method and the unitarized-distorted-wave approximation (UDWA), this model satisfactorily reproduces the experimentally obtained velocity dependence of the absolute ionization cross sections at intermediate impact velocities.

Differential cross sections for electron impact excitation out of the (…6s6p 1P1) state of barium

Differential cross sections for electron impact on excited state barium atoms have been measured for 20 eV incident electron energy and scattering angles of 5.5°, 9°, 13° and 16°. Results for the excitations (…6s6p 1P1) → X are presented with X = (…6s7s 1S0), (…6s7p 1P1), (…5d2 1D2 + …5d6p 1D2), (…5d2 3P2) and (…6s6d 1D2). Comparisons are made with existing theoretical results calculated in the convergent close coupling formalism and the unitarized distorted wave approximation.

Differential cross sections for electron-impact excitation out of the metastable levels of the barium atom

We report an experimental and theoretical investigation of low-energy electron scattering from 138Ba atoms prepared in the metastable 3D2 and 1D2 levels by laser-optical pumping. Differential cross sections were measured for excitation out of these metastable levels to a variety of higher-lying levels at electron-impact energies of 10, 20 and 36.7 eV. A comparison of experimental data with the results of theoretical approaches using the unitarized distorted-wave approximation and the convergent close-coupling scheme is given.

Electron-impact excitation of the level in ytterbium

We have measured and calculated differential cross sections for electron-impact excitation of the level in ytterbium at collision energies of 5, 10, 20, 40 and 80 eV. Calculations were made in the unitarized distorted-wave approximation. Measurements of the relative differential cross section, taking account of volume correction effects, were placed on an absolute scale by normalization to the theoretical integral cross section at 80 eV with extrapolation to lower energies based on the measured excitation function of Shimon et al (1981 Opt. Spektrosk. 50 571). Excellent agreement between theory and experiment is obtained in the regime of low momentum transfer.

Differential cross sections for electron impact excitation of Xe: I. Excitation of the five lowest levels; experiment and theory

Experimental and theoretical differential cross sections (DCSs) for electron impact excitation of the five lowest levels of xenon are reported. The experimental data were obtained at impact energies of 10, 15, 20 and 30 eV for scattering angles in the range of to . The scattering intensities for excitation of various levels with respect to that of the combined two lowest levels (representing the corresponding DCS ratios) were measured with conventional electrostatic electron energy-loss spectrometers. Absolute DCSs for excitation of the combined two lowest levels were derived from DCS ratios for excitation of the combined two lowest levels and elastic scattering and utilizing the elastic DCSs of Register et al. These DCS ratios were obtained from scattering intensity ratios measured with conventional electrostatic electron energy-loss spectrometers after correction for instrumental effects by utilizing electron time-of-flight measurements for determining the proper value of this ratio at scattering angle for each impact energy. The unitarized first-order many-body theory and the unitarized distorted-wave approximation were applied to obtain the theoretical differential cross sections for impact energies of 10, 15, 20, 30, 50 and 80 eV. The present experimental and theoretical results are compared with each other and with other available experimental and theoretical DCSs.

Differential cross sections for electron impact excitation of Xe: II. Excitation of the sixth to twentieth lowest levels; experiment and theory

Experimental and theoretical differential cross sections for electron impact excitation of Xe are reported for the lowest 6th to 20th levels. These data are an extension of the work discussed in the preceding paper. The theoretical work is based on the unitarized first-order many-body theory and unitarized distorted-wave approximation. The experimental data span the same respective range of electron impact energies and scattering angles as the preceding paper. The present theoretical and experimental data are compared with each other and with other existing experimental data.

Electron scattering from laser-excited barium: studies of the to transition

We report on measurements of the parameter and absolute differential cross section for electron-impact excitation of the state in barium from the metastable, isotropically populated level at 20 eV impact energy. The determination of these scattering parameters was facilitated by the utilization of a novel laser excitation geometry and measurement scheme. Along with our previous measurements of electron-impact coherence parameters for this transition we now have available a complete set of the five parameters which characterize the excitation of a P state by the scattering of unpolarized electrons from an isotropic (metastable) D level. Comparison of measured values with recent calculations carried out in the unitarized distorted-wave approximation reveals good agreement.

A measurement of electron impact coherence parameters by superelastic scattering from laser-excited 138Ba (. 6s6p 1P1)

Superelastic scattering of electrons from laser-excited 138Ba (. 6s6p 1P1) is used to measure the electron impact coherence parameters for excitation of this state. In particular, the variation with scattering angle of the charge cloud asymmetry parameter, Pl+, and the alignment angle parameter, gamma , have been determined at two incident electron energies. Comparison with recent theoretical results based on the unitarized distorted wave approximation has been made taking into account any possible distortion in the measurements due to the influence of a finite interaction volume. This comparison reveals good quantitative agreement for the gamma parameter over the range of scattering angles studied. Differences between the observed and predicted Pl+ parameters are small for near-forward scattering but become significant at the larger scattering angles studied.

Simplified distorted-wave treatment for asymmetric electron-capture processes.

It is shown that the distorted-wave amplitude for charge transfer can be transformed to a simpler form when one of the nuclear charges is much larger than the other. This amplitude is substituted into the unitarized distorted-wave approximation (UDWA) formula and applied to the process H(1s)+B/sup z/+..-->..H/sup +/+B/sup() z-1+/. It is confirmed that the simplified formula is valid down to a few keV/amu for z> or =10.

Exponential distorted-wave approximation for charge transfer in collisions of multicharged ions with atomic hydrogen

A new theoretical approach named the exponential distorted-wave approximation (EDWA) is developed and applied to electron-capture processes of multicharged ions from a hydrogen atom. The EDWA is an improvement of the unitarized distorted-wave approximation (UDWA) in that the EDWA takes into account the couplings among the final states which are neglected in the UDWA. The difference between the cross sections of the two methods is small except for the low-energy region less than a few keV/amu, and it is confirmed that the mixing among the final rearranged states does not play an important role in the processes studied here.

Electron-capture cross sections from He in collision with bare nuclear ions

The unitarized distorted-wave approximation (UDWA) is applied to single-electron-capture processes in the collision of naked ions with a helium atom, $B+\mathrm{He}(1{s}^{2})\ensuremath{\rightarrow}(B+e)+{\mathrm{He}}^{+}(1s)$, where $B={\mathrm{H}}^{+}, {\mathrm{Li}}^{3+}, {\mathrm{Be}}^{4+}, {\mathrm{C}}^{6+}, \mathrm{and} {\mathrm{O}}^{8+}$. We use the independent-electron model, in which the electron is assumed to move in an averaged Coulomb potential field with an effective nuclear charge. The UDWA cross section becomes more reliable as the charge of the incident ion increases, and good agreement with experimental data is obtained down to a few keV/amu for ${\mathrm{O}}^{8+}$+He.