Spin Polarization Parameters Research Articles

Spin polarization parameters and cross section for electrons colliding with silane molecules

A relativistic approach is employed to compute the differential and total cross sections, spin polarization P and the spin-polarization parameters T and U for the scattering of electrons from the silane molecule in the energy range 1–400 eV. The calculated spin-polarization parameters are compared with those for iso-electronic argon and atomic silicon. The calculated angular distribution shows a reasonably good agreement with the measured values.

Electron impact excitation of magnesium and zinc atoms in the relativistic distorted-wave approximation

A calculation based on a relativistic distorted-wave approximation has been carried out for the electron impact excitation of the , , and -states of magnesium and the and -states of zinc from their respective ground states. Differential cross sections, coherence and correlation parameters as well as the spin-polarization parameters were obtained at incident energies of 10, 20 and 40 eV, respectively. The results for magnesium are analysed and compared with other available theoretical and experimental data while those for the zinc atom are reported for the first time.

Spin polarization of photoelectrons from zinc atoms in the autoionization region

We have measured the energy dependence of the dynamical spin-polarization parameters for photoelectrons from zinc atoms in the wavelength region from 100 nm to 115 nm. The pronounced structure near the resonances found in previously measured absorption spectra also occurs in the spin-polarization parameters. From the experimental results the dipole transition matrix elements including the relative phase shift difference have been determined. The data are also compared with an existing R-matrix calculation and a new calculation employing semi-empirical Slater - Condon parameters.

Intra-atomic relativistic effects on the spin polarization in low-energy electron scattering from Ca, Sr, Ba, and Yb atoms.

The influence of intratarget relativistic effects on electron spin polarization is studied for low-energy electron scattering from Ca, Sr, Ba, and Yb atoms, for which a low-lying d-wave shape resonance is predicted. The motion of the scattering electron is described by solving the continuous-state Dirac-Fock equations plus a parameter-free correlation-polarization potential. The targets are represented using Dirac-Fock, Cowan's quasirelativistic Hartree-Fock, and nonrelativistic Hartree-Fock wave functions, in which the intra-atomic (also called the indirect) relativistic effects are incorporated in varying degrees. It is shown that the intra-atomic relativistic effects, in particular the spin dependence of the Dirac-Fock one-electron orbitals, create apparent quantitative changes in the spin polarization parameters around the d-wave shape resonances.

Relativistic effects in low-energy spin-dependent electron collisions with rare-gas atoms

The relativistic effects in low-energy spin-dependent electron scattering from rare-gas atoms Ar, Kr and Xe are analyzed by comparing the results obtained respectively with Dirac-Fock, Cowan's quasirelativistic Hartree-Fock and non-relativistic Hartree-Fock wave functions for target atoms. It is shown that the intra-target relativistic effects, in particular the explicit spin dependences of the one-electron orbitals of Dirac-Fock atomic wave function, create apparet quantitative changes in the spin polarization parameters at some collision energies and scattering angles.

Spin-resolved photoelectron spectroscopy of HBr in the resonance region of electron autoionization

The spin polarization parameters A and xi , the cross section sigma and the angular distribution parameter beta in outer shell photoemission from HBr were measured in the resonance region of electronic autoionization between the HBr+ X 2 Pi and HBr+ A 2 Sigma + thresholds using photoelectron spectroscopy with circularly polarized synchrotron radiation. In this region the photoelectron spectra display pronounced vibrational excitation of the X 2 Pi final ionic states. The energy dependence of the dynamical parameters is strongly influenced by electronic autoionization and predissociation of vibrational progressions of Rydberg states. The data for sigma and A are combined to obtain cross sections for the outgoing partial waves. A comparison of the experimental results with ab initio MQDT calculations of Lefebvre-Brion(1989) indicates that predissociation is more important than theoretically predicted.

Spin-polarization parameters and cross sections for electron scattering from zinc and lead atoms.

A relativistic approach is employed to compute the differential and integrated cross sections, spin-polarization P, and the spin-polarization parameters T and U for the scattering of electrons from zinc and lead atoms in the energy range 2.0--200 eV. The projectile-target interaction is represented both by real and complex optical potentials in the solution of the Dirac equation for scattered electrons. We compare our results for spin-polarization P with recent experiment and available theoretical calculations.

Spin polarization of Auger electrons from noble gases after photoionization with circularly polarized light

Spin polarization of Auger electrons arising from photoionization of atoms by circularly polarized light is studied theoretically. We present numerical calculations for the spin-polarization and angular anisotropy parameters of Auger decay for the Ar L3M2,3M2,3, Kr M4,5N2,3N2,3, Xe N4,5O1O2,3 and Xe N4,5O2,3O2,3 transitions. Our model employs Dirac-Fock wavefunctions using intermediate coupling for the final ionic states. We give complete data sets including relative intensities, angular distribution and all spin polarization parameters for the transitions considered, that are calculated consistently within one model.

Relativistic effects in spin-polarization parameters for low-energy electron-Cs scattering

Based on a Dirac R-matrix (close-coupling) calculation, the authors present results for various spin-polarization parameters for elastic and inelastic scattering of slow (Ekin<or approximately=2 eV) polarized electrons from unpolarized and polarized neutral Cs atoms in their ground state. Their results allow for a quantitative estimate of the importance of relativistic effects, and their calculated parameters clearly deviate from predictions obtained by just jj-recoupling the results of a non-relativistic calculation.

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.

Excitation of the 1,3P1 states of calcium, strontium and barium in the relativistic distorted-wave approximation

Calculations have been carried out in the relativistic distorted-wave approximation for the excitation of calcium, strontium and barium from their ground 1S0 states to the lowest lying 1,3P1 states of these atoms for incident electron energies in the range of 20 to 100 eV. The authors present results for differential cross sections, generalized spin-polarization parameters and electron-photon coherence parameters and compare them to experimental and previous theoretical results where available.

Spin Polarization of Elastically Scattered Electrons from Hg Atom

Calculations on differential cross sections and spin polarization parameters of elastical electron scattering with Hg atoms are performed for electrons in the energy range from 0.5 to 150eV. Dirac equation is used to describe the motion of scattered electrons in the target field, which includes static, exchange and correlation-polarization interactions. The agreement between theory and experiment is generally good.

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.

Spin polarization of electrons elastically scattered from barium atoms

Elastic scattering of electrons with barium atoms is calculated using a relativistic method. The total, differential and momentum transfer cross sections and the spin polarization parameters, S, T and U are presented from 0.04 to 150 eV. The influences of the loosely bound state in the p-orbital and the low-lying d-wave shape resonance on the spin polarization effect of the scattered electrons are shown to be significant at low collision energies.

Spin polarization of electrons elastically scattered from cadmium and zinc

The authors present results for spin polarization parameters for the low-energy elastic scattering of electrons from cadmium and zinc atoms. The calculations were carried out by solving the Dirac equations for the scattered electrons. The scattering potential included the Dirac-Fock static potential for the atoms plus a non-relativistic polarization potential calculated via the polarized-orbital method. Exchange was treated exactly. The authors compare their results for the asymmetry function with recent experimental results. They also present differential cross sections in comparison with recent experimental and theoretical data for cadmium.

Cross section and spin polarization for photoionization of the HI molecule: Rotationally resolved theoretical results in the spin–orbit autoionization region

The theoretical calculations of rotationally resolved total and differential cross sections and spin polarization parameters for the photoionization of HI molecule are presented. These calculations are based on the theoretical expressions derived by Raşeev and Cherepkov [Phys. Rev. A 42, 3948 (1990)]. The transition moments used in the calculation are taken from an ab initio calculation without rotation. Molecular rotation is included in the framework of a simplified model taking into account Hund’s case (c)–(e) frame transformation. The results of ab initio calculations of cross section and electron spin polarization parameters for state-to-state transition are obtained for the first time. Averaged over the rotational levels of the initial state and summed over the rotational levels of the final state of the ion, these calculations are compared with the recent measurements of the total cross section and integrated spin polarization parameters performed in Bielefeld.

Electronic structure and magnetism of Fe-Ge interfaces

The local electronic density of states (LDOS) has been calculated for Fe-Ge(110), Fe-Ge(111) and Fe-Ge(100) interfaces and neighbouring atomic planes using the recursion method. Interface states are found to exist within the mutual gaps of the constituent atoms and strongly depending on the local atomic environments. The most excess LDOSs are found for Fe-Ge(111) interface and the least for Fe-Ge(110). The magnetic moments for Fe atoms are found to decrease when the Fe layer approaches the interface boundary, which is in accord with the experiments. The electron spin polarization parameters evaluated from the LDOS are qualitatively consistent with experimental measurements.

ELASTIC SCATTERING OF SPIN ELECTRON BY Xe ATOM

In the processes of electron elastic scartering from spinless atoms, the incident electrons are treated as moving relativistically in an effective central potential V(r). The potential is calculated by relativistic self-consistent-field method with Slater local exchange approximations (i.e. Dirac-Slater SCF). Elastic scattering amplitudes are calculated by relativistic partial-wave expansion method. Then we calculated the differential cross section for electron elastic scattering from Xe atom and the spin polarization parameters. Detail comparisons of the theoretical and complete experimental results show the validity of the theoretical method adopted.

Angular anisotropy and spin polarization of Auger electrons from noble-gas atoms

The angular anisotropy coefficients and spin polarization parameters of Auger electrons for the transitions L3M2.3M2.3 in Ar, M4.5N2.3N2.3 in Kr and N4.5O2.3O2.3 in Xe atoms are calculated. The relativistic Dirac-Fock model with intermediate coupling is used for the description of the initial and final state of the Auger transition. The results of calculation are compared with earlier theoretical predictions and recent experimental data in the case of angular anisotropy. With a few exceptions good agreement with the experimental anisotropy is found.

Spin polarization of electrons elastically scattered from krypton

Spin-polarization parameters S, T and U are calculated for electrons elastically scattered by krypton atoms at energies from 3-150 eV. The target atom is represented by a frozen core in a continuum relativistic Hartree-Fock calculation with dipole and quadrupole polarization corrections. Because these corrections are applied to the target electrons as well as to the scattered electron, all electrons experience the same interactions and the scattering wavefunction is automatically orthogonal to the target orbitals. Cut-off parameters in the model polarization potential are obtained from independent calculations. The exchange connected with the electrostatic and polarization interactions is calculated exactly for both large and small components of the scattered wavefunction. The spin polarization S is compared with available experimental and theoretical results.