Application of R-matrix method to electron-H<Subscript>2</Subscript>S collisions in the low energy range

Electron-H₂S collision process is studied using the R-matrix method. Nine low-lying states of H₂S molecule are considered in the R-matrix formalism to obtain elastic integral, differential, momentum transfer and excitation cross sections for this scattering system. We have represented our target states using configuration interaction (CI) wavefunctions. We obtained adequate representation of vertical spectrum of the target states included in the scattering calculations. The cross sections are compared with the experiment and other theoretical results. We have obtained good agreement for elastic and momentum transfer cross sections with experiment for entire energy range considered. The differential cross sections are in excellent agreement with experiment in the range 3–15 eV. A prominent feature of this calculation is the detection of a shape resonance in ²B₂ symmetry which decays via dissociative electron attachment (DEA). Born correction is applied for the elastic and dipole allowed transition to account for higher partial waves excluded in the R-matrix calculation. The electron energy range is 0.025–15 eV.     

Perturbative calculation of the cross section in double ionization by high-energy Compton scattering

In this paper we investigate double ionization in high-energy Compton scattering from the He-atom including both the shake-off mechanism and a perturbative correction to that mechanism. The correction is calculated in second-order perturbation theory and includes Coulomb electron-electron interaction in addition to the correlation in the ground state of the He-atom. Our calculations for the ratio of double to single cross section cover the range from 30 to 300 keV of impact photon energy and explain the slow convergence of the ratio towards the asymptotic value.     

Elastic scattering of electrons from tetrahydrofurfuryl alcohol

Differential cross-sections (DCSs) for elastic scattering of electrons from tetrahydrofurfuryl alcohol (THFA), which can be considered as an analogue molecule to DNA sugar deoxyribose, were determined using crossed beam measurements for incident energies from 40 eV to 300 eV and scattering angles from 30° to 110°. The relative DCSs were measured both as a function of incident electron energy and scattering angle, allowing absolute calibration of the whole data set via normalization to a single point. The absolute calibration has been performed according to calculated absolute DCSs obtained by the corrected independent atom method using an improved quasifree absorption model. The calculated data-set includes DCSs and integral elastic and inelastic cross-sections in the incident energy range from 5 eV to 5000 eV. The theoretical results agree very well with the experimental ones, regarding the shape of DCSs. Moreover, the same theoretical procedure has been used to obtain DCSs for elastic electron scattering from a simpler deoxyribose analogue tetrahydrofuran (THF), which agree very well, both in shape and on the absolute scale, with the recent experimentally obtained absolute DCSs [A.R. Milosavljević et al., Eur. Phys. J. D 35, 411 (2005)]. The present results are also compared with the recent theoretical data for THF and THFA. Finally, according to both experimental and theoretical data, the DCSs for elastic electron scattering from THFA and THF molecules appear to be very similar both in shape and absolute scale.     

Elastic scattering of low-energy electrons by NO

We report elastic integral, momentum transfer and differential cross sections for electron scattering by N₂O for energies up to 50 eV. These results were obtained at the static-exchange approximation with the Schwinger Multichannel Method with Pseudopotentials [M.H.F. Bettega, L.G. Ferreira and M.A.P. Lima, Phys. Rev. A 47, 1111 (1993)]. In general our results show good agreement with experimental data and with other theoretical results but some discrepancies are found. We have also found a shape resonance around 4 eV in agreement with previous calculations using the R-matrix Method of Sarpal et al. [J. Phys. B 29, 857 (1996)]. On the other hand, the existence of a resonance at about 13 eV, clearly seen by the Schwinger Variational Iterative Method [Michelin et al., J. Phys. B 29, 2115 (1996)], can not be confirmed by our calculations. At this energy, our cross sections show a broad bump with no clear resonant behavior given by the eigenphase sum. Received: 13 November 1997 / Revised: 13 March 1998 / Accepted: 9 April 1998     

30-3000eV的正电子被O2、H2O及CH4散射的总截面计算

使用可加性规则，在Hartree-Fock水平上计算了30-3000eV的正电子被三个分子（O2、H2O及CH4）散射的总截面。计算正电子被三个分子散射的总截面时，首次使用了被束缚原子概念修正过的复光学势（这一复光学势考虑了分子中两个原子间的电子云重叠效应）。将正电子被这三个分子散射的总截面计算结果与实验结果及其它理论计算结果进行了比较，结果显示出在30-3000eV内，文中的计算结果与实验结果及其它理论计算结果具有较好的一致性。因此，可加性规则与修正后的复光学势相结合，完全适用于正电子被分子散射的总截面的计算。     

The viscosity cross-section for elastic electron-xenon collisions including electron spin polarization

The results of the evaluation of the viscosity cross-section for elastic electron-xenon collisions, taking into account the spin-orbit interaction of the continuum electron, in the energy interval from 0.1 eV to 50 eV are presented and discussed. The calculations are performed on the basis of three theoretically derived sets of phase shift data obtained by different authors and on the deduced relativistic expression for the viscosity cross-section in terms of phase shifts discerning the spin-up and spin-down states of the scattered electrons. Comparison with viscosity cross-sections, as evaluated from non-relativistic phase shifts extracted from experiments, strongly favours the relativistic results. The assumption of isotropic scattering is critically examined and the error induced by its use is shown to persist to the same extent as in non-relativistic calculations, at least in the energy region considered. Received: 22 April 1998 / Received in final form: 16 December 1998     

Geometric shielding corrections for total cross section calculations of electron scattering by CH4, C2H6, C2H3F3, C2H4, C2F4, C2Cl4 and C2Cl2F2 from 30–5000?eV

To quantify the changes in the geometric shielding effect in a molecule as the incident electron energy varies, an empirical fraction, which represents the total cross section contributions of shielded atoms in a molecule at different energies, is presented. Using this empirical fraction, the total cross sections for electron scattering by CH₄, C₂H₆, C₂H₃F₃, C₂H₄, C₂F₄, C₂Cl₄ and C₂Cl₂F₂ are calculated over a wide energy range from 30 to 5000 eV by the additivity rule model at the Hartree-Fock level. The quantitative total cross sections are compared with those obtained by experiment and other theories where available. Good agreement is attained above 100 eV.     

Elastic scattering of electrons by argon atoms

The partial wave method with a central potential has been applied to investigate the elastic scattering of electrons by the argon atoms in the intermediate energy range (100 eV − 1 keV). The central potential includes the effects of the static field, exchange and polarization. The results are in good accord with recent experimental data. A brief account of this investigation was presented at the X Int. Conf. on the Physics of Electronic and Atomic Collisions held at Paris in July 1977.     

Studies on vibrational excitation differential cross-sections of low-energy electron scattering from N2 molecule

The vibrational excitation differential cross-sections (DCS) of low-energy electron-N₂ scattering are studied using vibrational close-coupling (VCC) method and vibrational scattering potentials which include static, exchange and polarization contributions. By including the contributions of 18 partial waves, 20 vibrational states, and 16 molecular symmetries (up to Λ=7), the converged vibrational excitation (0↦2, 0↦3, 0↦4) DCS agree well with experimental results. Also obtained are converged vibrational (1↦0, 1↦1, 1↦2, 1↦3) DCS, with the impact energies being those of the main resonant peaks (1.92 eV, 1.90 eV, 1.62 eV, 1.63 eV).     

Low-energy electron scattering from copper

Differential cross sections for the elastic scattering of electrons from the ground states of copper for the configuration 3d¹⁰ 4s and the excitation state ²D with the configuration 3d⁹ 4s² have been calculated. Local density approximations to the exchange and correlation potentials have been used in these calculations, and it is confirmed that Hara exchange coupled with a Hedin-Lundqvist electron-gas-type correlation potential joined to an adiabatic polarization potential gives good predictions for differential cross sections. A comparison of the calculated results with other experimental and theoretical data are presented and discussed.     

Phase signatures in laser-assisted electron-atom collisions

We study electron-atom scattering in the presence of a laser field with elliptic polarization. We discuss the dependence of the differential cross sections for the cases of circular and linear polarizations as a function of scattering angle. Interesting typical signatures of the phase between the two components of the circular polarization of the laser field appear in the differential cross section.     

Elastic scattering of electrons by metastable hydrogen atoms in the presence of a resonant laser field

Within the framework of the rotating wave approximation the elastic scattering of electrons by metastable 2s state of hydrogen atoms is studied in the presence of a resonant laser field. The frequency of the circularly polarized laser field is chosen to match the 2s-3p transition frequency in the hydrogen atom. Variation of the cross section with laser intensity and with incident electron energy (50-150 eV) is investigated. Received: 18 July 1997 / Received in final form: 5 December 1997 / Accepted: 19 January 1998     

电子与锂和铍原子碰撞角分布的理论研究

用模型势方法研究电子与锂和铍原子弹性散射，计算了能量从０．１到１．０ｅＶ散射电子的角分布（微分散射截面），从理论计算中，看到在０．１－１．０ｅＶ能区内，随入射电子能量增加，电子被Ｌｉ和Ｂｅ原子散射的微分截面有相似变化，即小角微分散射截面越来越大     

Calculation of Elastic Scattering Properties in an Ultra-Cold ^85Rb-^85Rb Vapour

We report the calculation of the same-species elastic scattering properties for the ultracold rubidium-rubidium (^85Rb-^85Rb) system and the results are compared with other theoretical and experimental results in detail. We present an improved potential for triplet ground states of the Rb2 molecule, and calculate the scattering lengths αt and the effective range re using WKB and Numerov methods for two rubidium-85 collisions in the triplet state. Also, we investigate the convergence of these scattering properties, i.e. the dependence on core radius and K^0 parameter using quantum defect theory and the analytic calculations of scattering length obtained by Szmytkowski. In addition, we present evaporative cooling and other results that include phase shift and cross section at zero energy limit.     

Elastic scattering of electrons from water molecule

This paper uses the momentum--space optical potential method to calculate the e--H₂O scattering elastic cross sections at the energy range from 6 eV to 50 eV, and the differential cross sections in the angle from 0° to 180° at 40 eV and 50 eV. The polarisation is taken into account via an emphab initio equivalent-local potential. The cross sections are compared with experimental measurements and other theoretical calculations.     

Scattering and absorption differential cross sections for double photon Compton scattering

The scattering and absorption differential cross sections for nonlinear QED process such as double photon Compton scattering have been measured as a function of independent final photon energy. The incident gamma photons are of 0.662 MeV in energy as produced by an 8 Ci¹³⁷Cs radioactive source and thin aluminum foils are used as scatterer. The two simultaneously emitted photons in this process are detected in coincidence using two Nal(T1) scintillation detectors and a slow-fast coincidence set-up of 30 nsec resolving time. The measured values of scattering and absorption differential cross sections agree with theory within experimental estimated error.     

Absolute differential, elastic integrated and moment transfer cross sections for electron--OCS collisions at intermediate and high energies

A complex optical model potential modified by incorporating the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds between atoms in a molecule, is firstly employed to calculate the absolute differential, elastic integrated and moment transfer cross sections for electron scattering by OCS over the incident energy range from 200 to 1000\,eV using the additivity rule model at Hartree--Fock level. The calculated results are compared with those obtained by experiment and other theories wherever available, and good agreement is obtained over a wide energy range. It is shown that the additivity rule model together with the modified potential is completely suitable for calculating the absolute differential, elastic integrated and moment transfer cross sections of electron scattering by molecules such as OCS.     

Scattering of e± from N2 in the energy range 1 eV–10 keV

The differential, integrated elastic, inelastic, total, momentum transfer, viscosity, and ionisation cross sections for electron and positron scattering from the homonuclear diatomic nitrogen molecule over an incident energy range of 1?eV–10?keV are calculated using the additivity rule. Dirac partial wave analysis is employed to calculate the cross sections of the constituent atoms of molecules, using a complex optical model potential (OPM). Comparison of our results of the additivity rule with the available experimental data and other theoretical predictions is presented. Our findings produce reasonable results in intermediate and high energies.     

Elastic cross sections for electron--carbon scattering

We used the close-coupling optical (CCO) approach to investigate the open-shell carbon atom. The elastic cross sections have been presented at the energies below 90eV, and the present CCO results have been compared with other theoretical results. We found that polarization and the continuum states have significant contributions to the elastic cross sections. The present calculations show that the CCO method is capable of calculating electron scattering from open-shell atoms.