Multiple scattering calculation of double and single differential cross sections for ionization of hydrogen atoms by electrons at intermediate energies

The multiple scattering approach of Das and Seal, which was applied earlier to calculate the triple differential cross section for the ionization of atomic hydrogen by electrons is now used to calculate the double and the single differential cross sections for the same system. The range of the incident electron energy is taken to be 100–250 eV. The present results are compared with the measured results of Shyn and with the available distorted wave Born approximation results.     

Elastic electron scattering cross sections of oriented and aligned molecules

Elastic differential electron scattering cross sections of oriented methyl iodide are calculated using the independent atom model. Results are presented for two specific orientations of the ICH₃ molecule for the purpose of comparison with the fictitious molecule IC, similarly oriented, at electron energies of 600 eV and 40 keV. Cross sections are also calculated for IC with a large angular momentum. In a comparison of the results for different orientations of the angular momentum vector, including random orientation, large differences between the cross sections are evident. This sensitivity to the plane of rotation of the molecule suggests the possibility of determining the degree of alignment of the angular momenta of a beam of such molecules by electron diffraction.     

Correlation of the total cross section for electron scattering by molecules with 10–22 electrons, and some molecular parameters at intermediate energies

Accurate experimental values of the total cross section (σ_T) for electron scattering by molecules (CH₄, NH₃, N₂, CO and CO₂) in the energy range 0.5 to 5 keV have been analysed to obtain correlations with molecular properties. A formula for σ_T, as a function of the number of target electrons and molecular polarizabilities, has been deduced. This empirical expression reproduces to within 6% our experimental results for the abovementioned molecules and has been used to obtain results for other molecular targets with 10 to 22 electrons. Total cross sections show reasonable agreement with the experimental and theoretical data for this energy range.     

Measurements of total cross sections for electron scattering from helium and argon

A time-of-flight (TOF) electron spectrometer has been used to measure absolute total cross sections (TCS) scattered from helium and argon over the energy range from 1 to 50 eV. The TOF spectrometer and experimental procedure are described briefly, and experimental results are presented together with associated errors. The results are found to be in good agreement with other experimental and theoretical data.     

Total (elastic + inelastic) cross sections for electron scattering with bound and free germanium and lead atoms

Spherical complex optical potential (SCOP) approach has been used to compute the differential, total (elastic + inelastic) and momentum transfer cross sections for electrons scattering from the bound and free germanium and lead atoms in the energy range from 100–5000 eV. We find that the present calculated differential scattering cross sections (DCS) exhibit all important features (such as forward peaking, dip at middle angles and enhanced backward scattering) observed in other theoretical calculations and experimental measurements. The effect of absorption potential is generally to reduce the elastic cross section.     

Electron and positron atomic elastic scattering cross sections

A method was developed to calculate the total and differential elastic-scattering cross sections for incident electrons and positrons in the energy range from $\text{0.01}\text{eV}$ to $\text{1}\text{MeV}$ for atoms of Z=1–100. For electrons, hydrogen, helium, nitrogen, oxygen, krypton, and xenon, and for positrons, helium, neon, and argon atoms were considered for comparison with experimental data.First, the variationally optimized atomic static potentials were calculated for each atom by solving the Dirac equations for bound electron states. Second, the Dirac equations for a free electron or positron are solved for an atom using the previously calculated static potential accomplished (in the case of electrons) by “adjusted” Hara's exchange potential for a free-state particle. Additional to the exchange effects, the charge cloud polarization effects are considered applying the correlation-polarization potential of O'Connell and Lane (with correction of Padial and Norcross) for incident electrons, and of Jain for incident positrons.The total, cutoff and differential elastic-scattering cross sections are calculated for incident electrons and positrons with the help of the relativistic partial wave analysis. The solid state effects for scattering in solids are described by means of a muffin-tin model, i.e. the potentials of neighboring atoms are superpositioned in such a way that the resulting potential and its derivative are zero in the middle distance between the atoms. The potential of isolated atom is calculated up to the radius at which the long-range polarization potential becomes a value of −10⁻⁸.     

Collisions at thermal energy between metastable hydrogen atoms and hydrogen molecules: total and differential cross sections

A metastable hydrogen (deuterium) atom source in which groundstate atoms produced by a RF discharge dissociator are bombarded by electrons, provides a relatively large amount of slow metastable atoms (velocity 3–5 km/s). Total integral cross sections for H*(D*)(2s) + H₂(X ¹Σ _g ⁺ ,v=0) collisions have been measured in a wide range of relative velocity (2,5–30 km/s), by using the attenuation method. A significant improvement of accuracy is obtained, with respect to previous measurements, at low relative velocities. Total cross sections for H* and D*, as functions of the relative velocity, are different, especially in the low velocity range. H* + H₂ total differential cross sections have also been measured, with an angular spread of 3.6°, for two different collision energy distributions, centered respectively at 100 meV and 390 meV. A first attempt of theoretical analysis of the cross sections, by means of an optical potential, is presented.     

Absolute total cross sections for scattering of hydrogen atoms by argon,krypton and xenon

Absolute total cross sections for scattering of hydrogen atoms by argon, krypton and xenon were measured as a function of velocity in the range from 1.8 to 6.2 km/sec. An analysis in terms of Lennard-Jones (12.6) and (8.6) model potentials leads to estimates of the interatomic forces.     

Total scattering cross sections for ethylene by electron impact for incident electron energies from 1 to 2000 eV

We report total scattering cross sections for C₂H₄ molecule by electron impact. Calculations are performed by using two different quantum mechanical methods and they cover the energy range from 1 to 2000 eV. For low energy calculations up to 15 eV, UK molecular R‐matrix code through QUANTEMOL‐N software is used, while intermediate to high energy (15–2000 eV) calculations were carried out by applying spherical complex optical potential formalism. Comparison is made with earlier measurements and theoretical data wherever available. A shape resonance is detected around 2 eV due to the ²B_2g symmetry of an electronic state that corresponds to the temporary negative ion formation of ethylene. The differential cross sections are also calculated for the energy range from 1 to15 eV for the scattering angles between 0º and 180º. © 2013 Wiley Periodicals, Inc.     

Absolute cross sections for electron scattering from furan

We report results of measurements and calculations of absolute cross sections for electron scattering from furan molecules (C(4)H(4)O). The experimental absolute differential cross sections (DCSs) for elastic electron scattering were obtained for the incident energies from 50 eV to 300 eV and for scattering angles from 20[ordinal indicator, masculine] to 110[ordinal indicator, masculine], by using a crossed electron-target beam setup and the relative flow technique for calibration to the absolute scale. The calculations of the electron interaction cross sections are based on a corrected form of the independent-atom method, known as the screening corrected additivity rule (SCAR) procedure and using an improved quasifree absorption model. The latter calculations also account for rotational excitations in the approximation of a free electric dipole and were used to obtain elastic DCSs as well as total and integral elastic cross sections which are tabulated in the energy range from 10 to 10 000 eV. All SCAR calculated cross sections agree very well with both the present and previously published experimental results. Additionally, calculations based on the first Born approximation were performed to calculate both elastic and vibrationally inelastic DCSs for all the modes of furane, in the energy range from 50 eV to 300 eV. The ratios of the summed vibrational to elastic DCSs are presented and discussed. Finally, the present results for furan are compared with previously published elastic DCSs for the tetrahydrofuran molecule and discussed.     

Total cross sections for electron scattering from molecules: NH3 and H2O

By developing the semi-empirical formula recently obtained for total cross sections of electron scattering from diatomic molecules in the intermediate- and highenergy range, we calculate the total cross sections for electron scattering from molecules (NH₃ and H₂O) over an incident energy range of 10–1000 eV. The total cross sections have also been calculated by using the complex optical potential and the additivity rule. Compared with other available experimental and calculating data, excellent agreements have been achieved. The developed semi-empirical formula reflects that total cross sections for electron scattering from NH₃ and H₂O in the intermediate- and high-energy range quantitatively depend on the bond length.     

Electron–positron pair production and bremsstrahlung at intermediate energies in the field of heavy atoms

The Coulomb corrections (CC) to the processes of bremsstrahlung and pair production are investigated. The next-to-leading term in the high-energy asymptotics is found. This term becomes very essential in the region of intermediate energies. The influence of screening for CC is small for differential cross section, spectrum, and the total cross section of pair production. The same is true for the spectrum of bremsstrahlung, but not for the differential cross section, where the influence of screening can be very large. The corresponding screening corrections as well as the modification of the differential cross section of bremsstrahlung are found. A comparison of our results for the total cross section of pair production with the experimental data available is performed. This comparison has justified our analytical results and allowed to elaborate a simple ansatz for the next-to-leading correction. The influence of the electron beam shape on CC for bremsstrahlung is investigated. It turns out that the differential cross section is very sensitive to this shape.     

Differential cross sections for elastic scattering and electron detachment in collisions of halogen anions with noble gas atoms

Electron detachment in collision of halogen anions and noble gas atoms was investigated in the collision energy range of 500-3000 eV. Differential cross sections were determined both for elastic scattering and for the electron detachment process in the angular range of 0-3°. It was found that direct electron detachment, due to the interaction of the discrete ion-atom state with a continuum of states increases with increasing collisional energy. Furthermore, the experimental evidence indicates that direct detachment primarily occurs in a limited range of impact parameters. A model, based on angular coupling, is described which qualitatively explains these two experimentally observed features.     

Differential, partial and total electron impact ionization cross sections for SF(6)

Single and double differential ionization cross sections for the production of ions resulting from dissociative, single and double ionization of SF(6) by electron impact have been calculated using a semiempirical formulation based on the Jain-Khare approach. In addition, triple differential cross sections have been obtained for some of the doubly charged fragment ions at an incident electron energy of 100, 150, and 200 eV, respectively, and a fixed scattering angle of 30 degrees. As no previous data seem to exist for differential cross sections we have derived from these differential cross sections corresponding partial and total ionization cross sections from threshold up to 900 eV and compared those with the available theoretical and experimental data.     

Elastic nuclear scattering at intermediate and relativistic energies

The classical scattering cross section of two colliding nuclei at intermediate and relativistic energies is reevaluated. The influence of retardation and magnetic field effects is taken into account. Corrections due to electron screening as well as due to attractive nuclear forces are discussed. This paper represents an addendum to [1].     

Differential and total (e,2e) cross sections of simple polyatomic molecules

In this paper, we present a theoretical approach to calculate differential and total ionization cross sections of polyatomic molecules by fast electron impact. More exactly, we have studied the ionization of ammonia (NH(3)) and methane (CH(4)) molecules, and previous results concerning the H(2)O molecule ionization are reported for comparison. The calculations are performed in the distorted wave Born approximation without exchange by employing the independent electron model. The molecular target wave functions are described by linear combinations of atomic orbitals. To describe the interaction between the inactive target electrons and the slow ejected electron, we have introduced a distortion via an effective potential calculated for each molecular orbital. The present theoretical calculations agree well with a large set of existing experimental data in terms of multiple differential and total cross sections.     

Evaluation of the viscosity cross sections for elastic electron-atom collisions in krypton and xenon at low electron energies

The results of viscosity cross sections evaluations for elastic electron-atom scattering from rare gases krypton and xenon, carried out in the energy interval from 0.1 to 54.4 eV are presented and discussed. The evaluations are based on four independent sets of partialwave phaseshifts, one theoretical and three experimental, taken from literature. An analytical estimate for the contribution of all the terms not included in the summation, for truncation at any chosen value of the electron angular momentum, is derived. The validity of assumption of isotropic angular scattering is investigated in the energy range considered. The present results invariably show significant deviations from the values calculated with this assumption.     

Evaluation of cross sections for X-ray and high-energy electron scattering from molecular systems

An analytical and computationally efficient formalism for the evaluation of rotationally averaged cross sections for X-ray and high-energy electron scattering from molecular systems is given. Its application for both SCF and CI wave functions is discussed. © 1994 John Wiley & Sons, Inc.