D M Filipović

Critical minima in elastic electron scattering by argon

We determined experimentally two critical points in elastic electron scattering by argon where the differential cross section (DCS) attains its smallest values. The points were found to be at and at . Special attention was given to improve the angular resolution in order to determine the exact positions of the minima. These minima are important because they are a sensitive test of the validity of experimental procedures, and are used to verify theoretical predictions of DCS shapes and magnitudes, and of the polarization of scattered electrons. Normalized DCS were determined by measuring the angular distributions of elastically scattered electrons at incident energies of 10, 15, 20, 25, 30, 40, 50, 60, 75, 80, 90 and 100 eV in the angular range . Results are compared with the available experimental and theoretical data. In addition, integral, momentum-transfer, and viscosity cross sections were determined by numerical integration of the measured DCS extrapolated to and to .

Elastic and inelastic electron scattering by cadmium

Relative elastic scattering and excitation cross-sections of cadmium, up to the first ionization potential, are obtained from spectroscopic measurements on electrons with initial energies ranging from 3.4 to 85 eV. Relative differential cross sections are reported for excitation of the 55 0 (elastic), 53 P1 , 53 P)2 , 51 P1 , 63 S1 , 61 S0 , 51 D2 , 61 P1 , 71 S0 , (61 D2 -71 P1 ), 81 S0 and (71 D2 -81 P1 ) levels. Relative integrated scattering cross sections as well as momentum transfer and viscosity cross sections are also given.

Electron-impact excitation of the (n- 1)d9ns2np autoionizing states of cadmium (n = 5) and zinc (n=4)

Electron-impact excitation of the 53P 1 (12.062 eV) and 51P 1 (12.810 eV) 4d95s25p autoionizing states of Cd has been experimentally investigated at incident electron energies (E0) from 15 to 60 eV and scattering angles (θ) up to 40° (at E0 = 40 eV, θ = 2°–150°). The absolute differential cross sections (DCSs) at E0 = 40 eV were determined through normalization to the optical oscillator strengths. These DCSs were extrapolated to 0° and 180° and numerically integrated to yield integral, momentum transfer and viscosity cross sections. Energy-loss spectra for Cd were recorded from 11 to 18 eV, and 22 autoionizing states were identified at different impact energies. Electron-impact excitation of the 3d94s24p autoionizing states was observed in energy-loss spectra of Zn at E0 = 20, 60, 80 and 100 eV (θ up to 10°). The DCSs for Cd could not be compared with other results, because there are no available data in literature. The autoionizing energy levels and line widths are in good agreement with existing experimental and calculated values.

Electron scattering by ytterbium: I. Excitation of the 4f146s6p 1P1 resonance state and elastic collision

Differential cross sections (DCSs) for electron-impact excitation of the 4f 14 6s6p 1 P1 resonance state of ytterbium were measured at 10, 20, 40, 60 and 80 eV incident electron energies (E0) and scattering angles (θ ) between 2 ◦ and 150 ◦ . The absolute DCS scale for the 1 P1 state was determined through normalization of its relative DCSs to the optical oscillator strength using the forward scattering function method. DCSs for elastic electron scattering by ytterbium were measured at the same energies for θ between 10 ◦ and 150 ◦ . Elastic-to-inelastic intensity ratios were obtained from energy-loss spectra recorded with overall energy resolution of 65 meV (FWHM) and angular resolution of 1.5 ◦ . Both inelastic and elastic DCSs were extrapolated to 0 ◦ and 180 ◦ and numerically integrated to yield integral, momentum transfer and viscosity cross sections. Our results are compared with scarce experimental and theoretical data.

Differential and integrated cross sections for the electron excitation of the 4 1Po state of calcium atom

Differential cross section (DCS) data for excitation of the 4 1Po state (2.93 eV) of Ca atoms by electrons have been obtained using a crossed electron–atom beam technique. The measurements were divided into two groups. The first one consists of measurements at 10, 20, 40, 60 and 100 eV impact electron energies from 1° to 10° scattering angle interval. The second group of measurements are those at larger scattering angles (10°–150°) at the same energies except 100 eV. Absolute values have been obtained by normalizing generalized oscillator strengths (GOS) to optical oscillator strength (OOS) in the minimum momentum transfer squared (K2) limit. Integral, momentum transfer and viscosity cross sections have been determined from DCSs. A comparison is made with existing relativistic distorted wave calculation.

Electron-impact excitation of argon: I. The 4s´[½]1, 4p[½]1 and 4p´[½]0 states

We present absolute normalized differential cross sections (DCSs) for electron-impact excitation of the three individual electronic states of argon: 4s´[½]1 , 4p[½]1 and 4p´[½]0 . The measurements were performed with incident electron energies of 16, 20, 30, 40, 50 and 80 eV, scattering angles between 5° and 150° and an angular resolution of better than 2°. The absolute scale for the reference state (4s´[½]1 ) was established by experimental determination of inelastic-to-elastic intensity ratios for the 4s´[½]1 state at the above impact energies. Absolute inelastic DCSs for the other two states were determined using the intensity ratios of the peaks in the energy-loss spectra. The absolute DCSs were extrapolated to 0° and 180° and integrated numerically to yield integral, momentum transfer and viscosity cross sections.

Elastic electron scattering by a magnesium atom

Absolute differential cross sections (DCSs) for elastic electron scattering by a magnesium atom at incident electron energies of 10, 15, 20, 40, 60, 80 and 100 eV have been experimentally derived. The scattered electron intensities were measured over a wide range of scattering angles (θ) from 10° to 150°. The elastic-to-inelastic (3s3p 1P1 resonance state) intensity ratios at θ = 10° were measured separately. These ratios and DCSs for the resonance state (by Filipovic et al 2006 Int. J. Mass Spectrom. 251 66) were applied for the normalization. The absolute DCSs were extrapolated to 0° and 180° and then integrated to yield integral cross sections. The results were analysed and compared with available experimental data and theoretical calculations.

Differential and integrated cross sections for the elastic electron scattering by calcium atom

The experimental and theoretical studies of elastic electron scattering by calcium atom have been made. The experimental investigation was carried out using a crossed electron-atom beam technique. The measurements were performed at electron-impact energies (E0) of 10, 20, 40, 60 and 100 eV and for a range of scattering angles (θ) from 10° up to 150°. The absolute differential cross sections (DCSs) have been obtained from the elastic-to-inelastic (the resonant 41P0 state) intensity ratio at θ = 10° at each E0. Calculations have been performed in the optical potential approximation for the same E0 and θ between 0° and 180°. Results for DCSs and integrated (integral, momentum transfer and viscosity) cross sections are presented and compared with those predicted by existing calculations.

Electron scattering by ytterbium: II. Excitation of the 4f14(6s6p 3P1, 5d6s 1D2 and 6s7p 1P1) and 4f135d6s2 (7/2, 5/2)1 states

Differential cross sections (DCSs) for electron-impact excitation of the 4f146s6p3P1 (2.231 eV) state of ytterbium have been determined experimentally at incident electron energies, E0 = 10, 20 and 40 eV, and scattering angles (?) from 2? to 150? (at 10 eV from 10?). Also, DCSs for the 4f145d6s 1D2 (3.432 eV) and 4f135d6s2 (7/2, 5/2)1 (3.578 eV) states at E0 = 10 and 20 eV, and the 4f146s7p 1P1 (5.029 eV) state at 20 and 40 eV have been measured. These measurements were performed at ? between 10? and 150? for the 4f145d6s 1D2 and 4f135d6s2 (7/2, 5/2)1 states, and between 2? and 150? for the 4f146s7p 1P1 state. The inelastic-to-reference inelastic (the 4f146s6p 1P1 resonance state) intensity ratios were obtained from energy-loss spectra recorded with overall energy resolution of 65 meV (FWHM) and angular resolution of 1.5?. Using these ratios and DCSs for the reference state (Predojevi? et al 2005 J. Phys. B: At. Mol. Opt. Phys. 38 1329) the absolute inelastic DCSs were determined. In this way the obtained DCSs were extrapolated to 0? and 180? and numerically integrated to yield integral, momentum transfer and viscosity cross sections. Our results are compared with available calculated values and experimental data.

Elastic scattering of electrons by krypton in the energy range 20–260 eV

Elastic scattering of electrons by krypton atom was investigated both experimentally and theoretically. Differential cross sections (DCSs) were measured at fixed incident energies from 20 eV to 80 eV as a function of scattering angle (10°–150°). From 100 eV, DCSs were measured as a function of both incident electron energy (100–260 eV) and scattering angle (30°–110°), in small steps around minima. The energy dependence of the angular positions of DCS minima was determined. Theoretical results were obtained in terms of a model of phenomenological complex potential with allowance for spin–orbit interaction. Two data sets were calculated, with and without an absorption potential, and compared to experimental results. The improvements and deteriorations in agreement with measurements upon inclusion of absorption effects are discussed.