On the Theory of the Inelastic Scattering of Electrons by Helium Atoms

Miller, W.J.; Platzman, Robert L.

doi:10.1088/0370-1298/70/4/308

Cited by 115 publications

(20 citation statements)

References 9 publications

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“…We now introduce the stopping cross section for ion--ization asti, which is defined by There is no function Fl(t) that will yield a t-l l n t dependence in both Eqs. (30) and (31). Hence, we choose Fl to make the first term in both equations fall off faster than t-l l n t so as to become asymptotically negligible in both equations.…”

Section: Binary-encounter-dipole (Bed) Modelmentioning

confidence: 96%

“…Before we compare the BED and BEB cross sections with available experimental data, we discuss a simple and powerful way to graphically compare theoretical and experimental results &st proposed by Platzman to graphically represent SDCS's [2,30]. In his method, which we shall refer t o as the Platzman plot, the ratio Y of da(W, T)/dW to the Rutherford cross section, Eq.…”

Section: Comparisons W I T H Experimentsmentioning

confidence: 99%

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Binary-encounter-dipole model for electron-impact ionization

1994

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A theoretical model, which is free of adjustable or fitted parameters, for calculating electronimpact ionization cross sections for atoms and molecules is presented. This model combines the binary-encounter theory with the dipole interaction of the Bethe theory for fast incident electrons. The ratios of the contributions from distant and close collisions and interference between the direct and exchange terms are determined by using the asymptotic behaviors predicted by the Bethe theory for ionization and for stopping cross sections. Our model prescribes procedures to calculate the singly differential cross section (energy distribution) for each subshell using the binding energy, average kinetic energy, and the differential dipole oscillator strengths for that subshell. Then the singly differential cross section is integrated over the ejected electron energy to obtain the total ionization cross section. The resulting total ionization cross section near the threshold is proportional to the excess energy of the projectile electron. We found that this model yields total ionization cross sections for a variety of atoms and molecules from threshold to several keV which are in good agreement (-10% or better on average) with known experimental results. The energy distributions also exhibit the expected shapes and magnitudes. We offer a simpler version of the model that can be used when differential oscillator strengths are not known. For the ionization of ions with an openshell configuration, we found that a minor modification of our theory greatly improves agreement with experiment. PACS number(s): 34.80. Dp, 34.80.Gs, 34.80.K~

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Section: Binary-encounter-dipole (Bed) Modelmentioning

confidence: 96%

Section: Comparisons W I T H Experimentsmentioning

confidence: 99%

Binary-encounter-dipole model for electron-impact ionization

1994

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“…Hence, if we divide the SDCS by the "modified" Rutherford cross section, the result can be interpreted as the effective number of electrons in the target atom or molecule which participate in the ionizing collision of interest. This is the underlying idea for the Platzman plot (Miller and Platzman, 1957). In this plot, the ratio Y of the actual SDCS to the Rutherford cross section [Eq.…”

Section: B Platzman Plotsmentioning

confidence: 99%

Electron production in proton collisions with atoms and molecules: energy distributions

1992

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All known data on the energy distribution of secondary electrons from collisions of protons with atoms and molecules have been reviewed and differential cross sections have been collected. The two experimental methods used to obtain the data are discussed and possible sources of error pointed out. Theoretical treatments are reviewed and several methods of checking the consistency of the data are discussed. Two semiempirical models have been chosen to represent the differential cross sections, and parameters for these models are given which fit the average of the experimental data, subject to known constraints. Recommended values of differential cross sections are given for ten target gases by means of these models. All known data on the energy distribution of secondary electrons from collisions of protons with atoms and molecules have been reviewed and differential cross sections have been collected. The two experimental methods used to obtain the data are discussed and possible sources of error pointed out. Theoretical treatments are reviewed and several methods of checking the consistency of the data are discussed. Two semiempirical models have been chosen to represent the differential cross sections, and parameters for these models are given which fit the average of the experimental data, subject to known constraints. Recommended values of differential cross sections are given for ten target gases by means of these models. ©1992

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“…It seems desirable to point out here that the value of c", depends on details of the shape of the generalized oscillator strength, for all excitation energies, plotted as a function of momentum transfer (Miller and Platzman, 1957;Inokuti, 1971). Also, the wide variation of the derived values of bz and c~i n Table I is due in large part to relatively small variations in the rate of change of 0~x~as a function of U".…”

Section: CI Assical Theories Of Inner-shell Ion I2ationmentioning

confidence: 99%

Cross sections for ionization of inner-shell electrons by electrons

1976

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A survey is given of the available cross-section data for ionization of inner-shell electrons by incident electrons in the range of interest for electron-probe microanaiysis and for Auger-electron spectroscopy of solid surfaces. Owing to the paucity of data, the bulk of the discussion is limited to K-shell and I.-shell ionization of light atoms. Calculated, semiempirical, and experimental cross-section data have been intercompared graphically and through fits to the linearized Bethe equation for inner-shell ionization (the Fano plot). Almost all of the data could be satisfactorily fitted over the range 4 5 U", 5 30, where U", = Eo/E", , Eo is the incident electron energy, and E", the binding energy of electrons in the nl shell.From these fits, values could be obtained of the "effective" Bethe parameters b"I and c"&. Values of the parameter b", have also been derived from photoabsorption data and were found to be generally consistent with the ionization data if account was taken of the distribution of differentia oscillator strength with respect to excitation energy and the consequent expected variation of b", with incident electron energy. The derived "effective" Bethe parameters should not therefore be used outside the range of each fit.

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On the Theory of the Inelastic Scattering of Electrons by Helium Atoms

Cited by 115 publications

References 9 publications

Binary-encounter-dipole model for electron-impact ionization

Binary-encounter-dipole model for electron-impact ionization

Electron production in proton collisions with atoms and molecules: energy distributions

Cross sections for ionization of inner-shell electrons by electrons

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