Low-energy Elastic Cross Sections Research Articles

Low energy elastic cross section of fluoroacetylene by electron impact

SynopsisElectron impact low energy cross sections for fluoroacetylene is investigated for which there are no reported results in the literature. We have used various target models to compute accurate target properties and the best target model is used for the final scattering calculation. The fluorination effect in the cross section is studied by comparing the results with difluoroacetylene and acetylene.

Anomalously large low-energy elastic cross sections for electron scattering from the CF3 radical

Using a crossed electron-molecular-beam apparatus, absolute elastic cross sections for electron scattering from the CF3 molecule were measured. Differential cross sections were determined for incident electron energies in the range 7–50eV and over an angular range of 20–135°. Integral cross sections are subsequently derived from those data. The present measurements are compared to theoretical predictions using an extended independent atom model approach, and with earlier R-matrix and Schwinger Multichannel results. Agreement with theory is generally good at energies above 20eV, but for 20eV and below the measured cross sections are significantly larger than those predicted by all theories.

Convergence study of the close-coupling approach to positron-helium collisions

Positron-helium collisions have been studied using a two-center close-coupling method. Convergent, pseudoresonance-free cross sections have been obtained by using complete expansions on both the helium and positronium centers. The low energy elastic cross sections, phase-shifts and total cross sections are compared with experimental data and results of other theories.

Convergent close-coupling calculations of positron-helium collisions

The convergent close-coupling method, which includes positronium formation, is used to calculate positron-helium scattering. Low-energy elastic cross sections and Ore-gap total cross sections are calculated using equal number of pseudo-states from the atomic and positronium centers. We show that in the Ore-gap region only two-center expansions can give convergent results.

Elastic cross sections of 1s-muonic atoms at low energies in non-adiabatic approach

The low-energy elastic cross-section in collisions of a muonic atom with the hydrogen isotope is investigated, employing a new wave function (trial) and using the coordinate-space Faddeev–Hahn model. The wave function includes non-adiabatic terms. Our results of s–wave cross-sections are given, at the tμ(1s) + d scattering. Calculated cross-sections are in good accord with the results published by Chiccoli et al., while having no good agreement with other recent reports.

Scattering ofH¯(1s)off metastable helium atom at thermal energies

Quantal calculations for scattering of ground-state antihydrogen by metastable $(n=2S)$ helium atoms have been performed using the nonadiabatic, atomic orbital expansion technique at thermal energies. The zero-energy elastic cross sections of the present systems are much greater than the corresponding value for the ground-state helium target. The low-energy elastic cross section for the singlet metastable helium $[\mathrm{He}(2\phantom{\rule{0.2em}{0ex}}^{1}S)]$ target is higher than the corresponding value when the target is in the metastable triplet state $[\mathrm{He}(2\phantom{\rule{0.2em}{0ex}}^{3}S)]$.

Configuration-interaction calculations of positron binding to zinc and cadmium

The configuration-interaction method is applied to the study of positronic zinc ${(e}^{+}\mathrm{Zn})$ and positronic cadmium ${(e}^{+}\mathrm{Cd}).$ The estimated binding energies and annihilation rates were 0.003 73 hartree and $0.42\ifmmode\times\else\texttimes\fi{}{10}^{9} {\mathrm{sec}}^{\ensuremath{-}1}$ for ${e}^{+}\mathrm{Zn}$ and 0.006 10 hartree and $0.56\ifmmode\times\else\texttimes\fi{}{10}^{9} {\mathrm{sec}}^{\ensuremath{-}1}$ for ${e}^{+}\mathrm{Cd}.$ The low-energy elastic cross section and ${Z}_{\mathrm{eff}}$ were estimated from a model potential that was tuned to the binding energies and annihilation rates. Since the scattering lengths were positive ${(14.5a}_{0}$ for Zn and ${11.6a}_{0}$ for Cd) the differential cross sections are larger at backward angles than at forward angles just above threshold. The possibilities of measuring differential cross sections to confirm positron binding to these atoms is discussed.

Resonances in positronium–rubidium and positronium–cesium scattering

Scattering of ortho positronium (Ps) by cesium and rubidium atoms has been investigated employing a three-Ps-state coupled-channel model with Ps(1s,2s,2p) states using a time-reversal-symmetric regularized electron-exchange model potential. We find a narrow S-wave singlet resonance at 5.057 eV of width 0.003 eV in the Ps–Rb system and at 5.067 eV of width 0.003 eV in the Ps–Cs system. Singlet P-wave resonances in both systems are found at 5.3 eV of width 0.4 eV. Singlet D-wave structures are found at 5.4 eV in both systems. The pronounced P- and D-wave resonances in these systems lead to easily detectable local minima in the low-energy elastic cross sections. We also report results for elastic and Ps-excitation cross sections for Ps scattering by Rb and Cs.

Calculation of low-energy elastic cross sections for electron-CF4 scattering

A new computational approach has been used to evaluate the rotationally summed, vibronically elastic integral cross sections from the scattering of slow electrons (energy ranging from 1.0 eV up to 40.0 eV) by tetrafluoromethane molecules in the gas phase. The various symmetry components have been analyzed using the exact static exchange approximation and also by including a nonempirical, model polarization potential employed before by our group. A comparison with earlier calculations and with existing experiments allows us to assign the symmetries of the shape resonances in the 5–30 eV energy region which are seen by experiments and are also shown by the present calculations.

Irregular solutions of the s-wave radial Schrödinger equation for van der Waals potentials

Simple ideas based on quantum chromodynamics suggest that the strong nuclear force might possess a long-range van der Waals component. Such a component, if it exists, would be most apparent in low-energy interactions between pairs of hadrons, at least one of which is neutral. In this article, as the initial part of a program to set limits on the magnitude of the strength of such a van der Waals interaction, we construct low-energy series expansions of the two irregular solutions f0(±k,r) to the s-wave Schrödinger equation that describes the interaction of a pair of particles interacting through a potential with a van der Waals tail of the form V(r)∼−λℏcrN−10 /rN, for arbitrary values of the potential parameters, λ, r0, and N. Accurate approximation schemes based on the series expansions are developed, and the results are used to obtain an expression for the low-energy elastic cross section. The effects of the van der Waals component of this interaction are clearly evident in the energy dependence of the cross section.

Independent-particle-model study of electrons elastically scattering from oxygen

The independent-particle model of Green, Sellin, and Zachor is adjusted to describe the inner and singly excited states of neutral oxygen. It is found that the entire spectrum can be fitted using only two parameters. With the addition of a polarization potential, the ground state of ${\mathrm{O}}^{\ensuremath{-}}$ is also fitted with a Green-Sellin-Zachor independent-particle model. Low-energy elastic cross sections for electrons on neutral oxygen are then obtained. The calculated cross section fit the data reasonably well. The neutral-oxygen calculations are then extrapolated to zero energy using modified effective-range theory from which we obtain a scattering length of $0.485{a}_{0}$. At higher energies, the results of partial-wave calculations are compared to a two-parameter analytic Born approximation.

Elastic Scattering of Slow Electrons by Lithium Atoms in the Polarized-Orbital Approximation

We have calculated the low energy elastic cross section for electrons incident on lithium atoms via the polarized-orbital method proposed by Temkin. The only further approximations made are the exclusion of core polarization and the use of frozen core Hartree–Fock wave functions. Quite good agreement with previous close-coupling calculations are obtained in the energy range 0.5–3 eV. Surprisingly, the threshold resonance behavior predicted by the close-coupling results is obtained when exchange is neglected, but not when the full polarized-orbital method is used.

Scattering of Low-Energy H— Ions in Helium, Neon, and Argon

Elastic and inelastic cross sections have been measured for the scattering of H— ions in helium, neon, and argon gases, at incident ion energies in the range 5 ev to 350 ev. One term interaction potentials of the form V=—K/rn were calculated from the low-energy elastic cross sections. These potentials were: for H— and He, V=—2.90/r3.01 ev for r=1.30 A to 1.90 A; for H— and Ne, V=—4.17/r2.80 ev for r=1.00 A to 1.78 A; and for H— and A, V=—7.82/r3.40 ev for r=1.23 A to 2.12 A. The observed inelastic cross sections are interpreted as cross sections for electron detachment from H—; they show a similar behavior with ion energy W in the three cases, appearing at W between 0 and 5 ev, rising rapidly to W=40 ev, and then rising very slowly to W=350 ev. Evidence was found for positive ion formation in H— collisions with Ne and A atoms at ion energies above 100 ev.