Present Differential Cross Sections Research Articles

Ionization Cross Sections of Hydrogen Molecule by Electron and Positron Impact.

We present ionization cross sections of hydrogen molecules by electron and positron impact for impact energies between 20 and 1000 eV. A three-body Classical Trajectory Monte Carlo approximation is applied to mimic the collision system. In this approach, the H2 molecule is modeled by a hydrogen-type atom with one active electron bound to a central core of effective charge with an effective binding energy. Although this model is crude for describing a hydrogen molecule, we found that the total cross sections for positron impact agree reasonably well with the experimental data. For the electron impact, our calculated cross sections are in good agreement with the experimental data in impact energies between 80 eV and 400 eV but are smaller at higher impact energies and larger at lower impact energies. Our calculated cross sections are compared with the scaled cross sections obtained experimentally for an atomic hydrogen target. We also present single differential cross sections as a function of the energy and angle of the ejected electron and scattered projectiles for a 250 eV impact. These are shown to agree well with available data. Impact parameter distributions are also compared for several impact energies.

Triple differential cross sections for single ionization of an atom by bare ion impact

We present triple differential cross sections (TDCSs) for single ionization of atoms by proton and highly charged bare ions impact by means of the three-body formalism of the first Born, two-Coulomb wave and three-Coulomb (3C) wave (3CW) methods, respectively. The TDCS has been calculated both in the scattering and perpendicular planes. The purpose of this work is to investigate the validity of different methods as well as the role of interaction between projectile and residual-target-ion in the final state for weak perturbation strength with low electron emission energy at several momentum transfers. By comparing our calculations with experimental data, overall, the 3CW predicts better agreement with experiments than other calculations in the scattering plane. In the perpendicular plane, all calculations deviate from experimental data with increasing transverse momentum transfer for p − He collision. At low momentum transfer, the location of binary peak obtained by the first Born approximation calculation is well established with the experiment for proton impact. On the other hand, the 3CW model is in much better agreement with experiments, both in absolute values and peak position for highly charged impact. Finally, the strong influence of the internuclear Coulomb distortion on TDCS has been observed at low and intermediate momentum transfer.

Joint experimental and theoretical study on low-energy elastic electron scattering by gaseous alkynes: Differential cross sections, shape resonances, and methylation effects

A detailed comparison of experimental and theoretical elastic cross sections for low-energy electron scattering by ethyne (${\mathrm{C}}_{2}{\mathrm{H}}_{2}$), taken earlier in our group by Gauf et al. [Phys. Rev. A 87, 012710 (2013)], and some of its methylated derivatives, propyne (${\mathrm{C}}_{3}{\mathrm{H}}_{4}$), and the isomers 1-butyne and 2-butyne ($n\ensuremath{-}{\mathrm{C}}_{4}{\mathrm{H}}_{6}, n=1,2$), taken here, are presented. The present differential cross sections were measured at incident electron energies ranging from 1 eV to 30 eV and for scattering angles from ${5}^{\ensuremath{\circ}}$ to ${130}^{\ensuremath{\circ}}$ using the relative flow method with an aperture gas source. Our earlier work was taken over a larger energy range of up to $100\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. The theoretical calculations were carried out for impact energies up to $30\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, employing the Schwinger multichannel method with pseudopotentials in the static-exchange plus polarization approximation. In addition to the differential cross sections, we present the integral and momentum transfer cross sections with which we discuss the shape resonances present in these systems and other physical phenomena, such as the presence of Ramsauer-Townsend minimum. We also compare our theoretical and experimental results with previous data that are available in the literature.

Elastic Positron Collisions with 1,1-Difluoroethylene.

This work reports a theoretical investigation on the elastic-positron collision with the 1,1-difluoroethylene molecule for energies up to 10 eV. We have employed the Schwinger multichannel method in the static-plus polarization level of approximation to obtain the integral and differential cross sections. In order to account for the long-range potential due to the permanent dipole moment of the target, the Born-closure procedure has been employed. Also, our present differential cross sections have been applied to estimate a correction to the total cross section measurements available in the literature.

Elastic scattering of electrons by barium atoms using the distorted wave method

Differential and integral cross sections of elastic scattering of electrons by barium atoms at intermediate energies (10 – 200 eV) were calculated using the distorted wave method. Being an elastic scattering both the initial and final distortion potentials were taken as the static potential of a barium atom in the initial state. The distorted waves are determined by the partial wave expansion method by expanding them in terms of spherical harmonics while the radial equation corresponding to distorted waves is evaluated using the Numerov method. A computer program DWBA1, for scattering was modified to perform numerical calculations for scattering and the results obtained are compared with the experimental and theoretical results available. The present integral cross sections are in good qualitative agreement with the experimental results and most of the theoretical results. For energies in the range 30 – 100 eV the present differential cross sections are in satisfactory agreement with the other theoretical and experimental results.

A Complete Cross Section Data Set for Electron Scattering by Pyridine: Modelling Electron Transport in the Energy Range 0–100 eV

Electron scattering cross sections for pyridine in the energy range 0–100 eV, which we previously measured or calculated, have been critically compiled and complemented here with new measurements of electron energy loss spectra and double differential ionization cross sections. Experimental techniques employed in this study include a linear transmission apparatus and a reaction microscope system. To fulfill the transport model requirements, theoretical data have been recalculated within our independent atom model with screening corrected additivity rule and interference effects (IAM-SCAR) method for energies above 10 eV. In addition, results from the R-matrix and Schwinger multichannel with pseudopotential methods, for energies below 15 eV and 20 eV, respectively, are presented here. The reliability of this complete data set has been evaluated by comparing the simulated energy distribution of electrons transmitted through pyridine, with that observed in an electron-gas transmission experiment under magnetic confinement conditions. In addition, our representation of the angular distribution of the inelastically scattered electrons is discussed on the basis of the present double differential cross section experimental results.

Elastic electron scattering by SnCl4 in the low-energy regime

We report integral, differential, and momentum-transfer cross sections for elastic scattering of electrons by tin tetrachloride (SnCl4). The scattering cross sections were calculated with the Schwinger multichannel method implemented with norm-conserving pseudopotentials, in the static-exchange and static-exchange plus polarization levels of approximation, for energies ranging from 0.01 eV to 30 eV. Our calculations show the presence of two resonant structures in the integral cross section located at 3.3 eV and 7.5 eV in the static-exchange approximation, while in the static exchange plus polarization approximation, these structures are centered around 1.2 eV and 5.6 eV. The symmetry decomposition of the integral cross section in both C2v and Td groups along with the analysis of the eigenvalues of the scattering Hamiltonian supports that the first resonance belongs to the T2 symmetry and the second to the E symmetry. Our results also support that the ground state of the negative ion SnCl4− is stable, in agreement with the results of previous studies. The low-energy behavior of the s-wave cross section and the s-wave eigenphase support the presence of a Ramsauer–Townsend minimum at 0.1027 eV. The present integral, differential, and momentum-transfer cross sections in the static exchange approximation are in good agreement with the previous results reported by Joucoski and Bettega [J. Phys. B: At. Mol. Opt. Phys. 35, 4953 (2002)]. In the static exchange plus polarization approximation, our integral cross section shows a good qualitative agreement with the measured grand-total cross section of Możejko et al. [J. Chem. Phys. 151, 064305 (2019)].

Low-Energy Electron Scattering from Dimethyl Ether.

Low-energy (0.1 to 15 eV) R-matrix calculation is performed for dimethyl ether molecule. Electronic excitation and momentum transfer cross section for low energies are reported for the first time. Present differential cross sections show good agreement with previous data in terms of shape but are significantly higher in magnitude. Apart from low energies, we have also performed high-energy calculation (11-5000 eV) using spherical complex optical potential formalism. To deal with the molecular nature of the present target, we have applied an effective potential method in our computation for the first time. Good consistency can be seen at the overlapping energies of the two calculations.

Electron scattering from allene and 1,2-butadiene

The Schwinger multichannel method is employed to calculate elastic cross sections for electron collisions with allene (C3H4) and 1,2-butadiene (C4H6) molecules. Integral elastic and differential cross sections were obtained for both molecules in the static-exchange and static-exchange-polarization approximations, for energies from 0.1 eV to 10 eV. Both molecules have a π* shape resonance centered at 2.4 eV in the integral cross section, and a Ramsauer-Townsend minimum was found at around 0.34 eV in the allene cross section. The present differential elastic cross sections are compared between the two molecules and with the experimental and theoretical data available. Some of the features in the cross sections are analyzed and discussed in the context of the methylation effect, since the 1,2-butadiene molecule can be viewed as the methylated allene molecule. Electronic structure calculations are also performed in order to help in the interpretations of our results.

Triple and double differential cross sections for ionization of atomic hydrogen by positive-bare ions impact

In the present study, the triple and double differential cross sections for ionization of atomic hydrogen from the ground state (1s) and first excited state (2s) by H+, He2+ and Li3+ positive-bare ions impact have been studied. Calculations have been performed using the second Born approximation. The closure approximation was employed, and the final integrals were solved using Gauss-Legendre and Gauss-Laguerre numerical methods. The double differential cross section of atomic hydrogen ionization from the ground state by protons at 75 keV, scattering angle (θs) from 0 to 1 mrad, and the ejected electron energies 16.4, 26.4, 36.4 and 39.4 eV are compared to available experimental and theoretical results. The results of the triple differential cross section from 1s and 2s states of atomic hydrogen in collision with H+, He2+ and Li3+ positive-bare ions at certain scattering angles of projectile (θs) are also presented.

Associated production of SM Higgs with a photon in type-II seesaw models at the ILC

We consider the production of a single Standard Model (SM) Higgs boson (h^0) in association with a photon at the future Linear collider (LC) in the context of a type-II seesaw model. The type-II seesaw model extends the SM particle content by adding one triple Higgs where its Higgs coupling is a key parameter of the scalar potential triggering the electroweak symmetry-breaking mechanism in the SM. It is a well motivated model since it provides neutrino masses and mixing. The LC presents a particularly interesting possibility to probe Higgs couplings due to the clean beams in the initial state. We study the one loop processes e^+e^- rightarrow h^0gamma and e^-gamma rightarrow e^- h^0, we show that it is possible to correlate the total cross section predictions with the couplings h^0gamma gamma and h^0gamma Z which are sensitive to the presence of singly and doubly charged Higgs. For parameter points allowed by the current experimental constraints, our numerical results show that the effect of H^pm and H^{pm pm } can be as large as ± 25% with respect to the SM predictions. For both processes, we also present differential cross section for different center of mass energy.

Theoretical and experimental cross sections for electron scattering from halothane

We report a joint theoretical and experimental study on elastic scattering of electrons from halothane (CF3CHBrCl). The theoretical differential, integral and momentum transfer cross sections were obtained with the Schwinger multichannel method implemented with pseudopotentials (SMCPP), and with the independent atom model with screening corrected additivity rule including interference effects (IAM-SCAR+I). The differential cross sections measurements were conducted for incident electron energies of 10, 20, 30 and 50 eV, while the scattered electron angular range varied from 7° to 100°. At these energies the present experimental differential cross sections are in reasonable agreement with both SMCPP and IAM-SCAR+I calculations. As expected, the two theoretical methodologies agree well with each other as the electron impact energy increases. We also discuss the presence of low-energy resonances and a bound anion state identified in our SMCPP calculations.

Investigations of the valence-shell excitations of molecular ethane by high-energy electron scattering.

The differential cross sections and generalized oscillator strengths for the low-lying excitations of the valence-shell 1eg orbital electron in ethane have been measured for the first time at a high incident electron energy of 1500 eV and a scattering angular range of 1.5°-10°. A weak feature, termed X here, with a band center of about 7.5 eV has been observed, which was also announced by the previous experimental and theoretical studies. The dynamic behaviors of the generalized oscillator strengths for the 3s (8.7 eV), 3s+3p (9.31 eV, 9.41 eV), and X (∼7.5 eV) transitions on the momentum transfer squared have been obtained. The integral cross sections of these transitions from their thresholds to 5000 eV have been obtained with the aid of the BE-scaling (B is the binding energy and E is the excitation energy) method. The optical oscillator strengths of the above transitions determined by extrapolating their generalized oscillator strengths to the limit of the squared momentum transfer K2 → 0 are in good agreement with the ones from the photoabsorption spectrum [J. W. Au et al., Chem. Phys. 173, 209 (1993)], which indicates that the present differential cross sections, generalized oscillator strengths, and integral cross sections can serve as benchmark data.

Interference in fast bare ions colliding with diatomic molecules

SynopsisTotal as well as differential cross sections for electron capture in collisions of bare ions with diatomic molecules have been investigated at incident projectile energies ranging from 20 to 1000 keV/amu in the framework of distorted wave (DW) approximation. The present DW calculation is the simplest possible quantum calculation for this system. The present differential cross sections (DCS) are in good agreement with the shape of the observed angular dependence at forward angles.

Elastic Differential Cross Sections for Electron Scattering with Dichloromethane

SynopsisIn the present study joint experimental and theoretical elastic differential cross sections for electron scattering from dichloromethane in the incident electron energy region 7 to 50eV are discussed.

Adiabatic-nuclei calculations of positron scattering from molecular hydrogen

The single-center adiabatic-nuclei convergent close-coupling method is used to investigate positron collisions with molecular hydrogen (${\mathrm{H}}_{2}$) in the ground and first vibrationally excited states. Cross sections are presented over the energy range from 1 to 1000 eV for elastic scattering, vibrational excitation, total ionization, and the grand total cross section. The present adiabatic-nuclei positron-${\mathrm{H}}_{2}$ scattering length is calculated as $A=\ensuremath{-}2.70{a}_{0}$ for the ground state and $A=\ensuremath{-}3.16{a}_{0}$ for the first vibrationally excited state. The present elastic differential cross sections are also used to ``correct'' the low-energy grand total cross-section measurements of the Trento group [A. Zecca et al., Phys. Rev. A 80, 032702 (2009)] for the forward-angle-scattering effect. In general, the comparison with experiment is good. By performing convergence studies, we estimate that our ${R}_{m}=1.448{a}_{0}$ fixed-nuclei results are converged to within $\ifmmode\pm\else\textpm\fi{}5%$ for the major scattering integrated cross sections.

Excitation of vibrational quanta in furfural by intermediate-energy electrons.

We report cross sections for electron-impact excitation of vibrational quanta in furfural, at intermediate incident electron energies (20, 30, and 40 eV). The present differential cross sections are measured over the scattered electron angular range 10°-90°, with corresponding integral cross sections subsequently being determined. Furfural is a viable plant-derived alternative to petrochemicals, being produced via low-temperature plasma treatment of biomass. Current yields, however, need to be significantly improved, possibly through modelling, with the present cross sections being an important component of such simulations. To the best of our knowledge, there are no other cross sections for vibrational excitation of furfural available in the literature, so the present data are valuable for this important molecule.

Hartree-Fock calculation of the differential photoionization cross sections of small Li clusters.

Cross sections and angular distribution parameters for the single-photon ionization of all electron orbitals of Li2-8 are systematically computed in a broad interval of the photoelectron kinetic energies for the energetically most stable geometry of each cluster. Calculations of the partial photoelectron continuum waves in clusters are carried out by the single center method within the Hartree-Fock approximation. We study photoionization cross sections per one electron and analyze in some details general trends in the photoionization of inner and outer shells with respect to the size and geometry of a cluster. The present differential cross sections computed for Li2 are in a good agreement with the available theoretical data, whereas those computed for Li3-8 clusters can be considered as theoretical predictions.

Four-body treatment of the single-electron capture in energetic proton–helium collisions

Both the post and prior versions of the four-body Coulomb–Born distorted wave (CBDW-4B) approximation are applied to calculate the single-electron capture differential and integral cross sections in collision of the fast protons with helium atoms. The outlined model satisfies the correct boundary conditions, and the incident energy is considered in a range of 20 to 1000 keV for which the applied approach is valid. For proton–helium collisions, the CBDW-4B method exactly coincides with the four-body first-order Jackson–Schiff approximation (JS1-4B). The influence of the static and dynamic electronic correlations on the cross sections is investigated. The ground state of the helium atom is described using two different wave functions to show the influence of the static correlation on the captured cross sections. In order to illustrate the validity of the present method, the obtained results are compared with the other theoretical investigations as well as the available experimental measurements. Although the overall agreement of the present numerical differential cross sections (DCS) with the reported experimental findings is acceptable, contrary to our general expectation, the three-body version of the formalism gives a better description of the angular distribution of the captured cross sections. However, for integral cross sections, the agreement of the four-body results with the reported measurements is better than those of three-body formalism.

Electron impact ionization of helium: test of screening potential in the final state

The triple differential cross sections for electron impact ionization of a helium atom is studied using the 70.6 eV incident electron. The initial state which includes both bound and continuum wave functions is calculated using the Hartree–Fock approximation. The final state continuum electron wave functions are computed in the potential of the core. The interaction potential between the two continuum electrons in the final state is approximated with the screening potential determined variationally. It is found that there is qualitative agreement between the present triple differential cross section results and the available experimental and the other theoretical data for equal and unequal sharing of 46 eV excess energy by the two final state continuum electrons. It is concluded that the screening potential which is an approximation to the actual Coulomb interaction potential between the two final state continuum electrons can produce qualitative agreement with the experiment.