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A theoretical study of the double-differential cross sections (DDCS) for ejection of electron from hydrogen atom in ground state by the impact of $$\hbox {C}^{6+}$$ ion with energy values 1 and 2.5 MeV/amu is presented. For the final state, we use a continuum distorted wave that contains the product of two Coulomb distortions due to the projectile–electron and target–electron Coulombic interactions for which it is called the two-Coulomb-wave (2CW) model. In this paper, the energy and angular distributions of DDCS for electron emission from atomic hydrogen have been investigated. The ejected electrons are influenced by the combined fields of the target and the projectile ion. Comprehensive comparisons are made between the three-Coulomb-wave model (Jana et al. in Eur Phys J D 66:243, 2012) and the present 2CW model. The emitted electron, the incident projectile ion and the residual ion are considered to be in the same plane. It is found that the two-centre effect has a major influence on the observed forward–backward angular asymmetry in the angular distribution of electron emission spectra. The region of the binary encounter peak is analysed in detail. The present computed results have been compared with the available experimental results as well as other theoretical calculations based on the first Born approximation and the continuum distorted wave eikonal initial state approximation. Moreover, the present computed results are in better agreement with the available experimental data for electron emission cross sections.

Total as well as angular-differential cross sections for single electron capture have been investigated in collision of bare ions ($$H^{+}$$, $$He^{2+}$$ and $$Li^{3+}$$) with hydrogen molecules at intermediate and high collision energies with special emphasis on finding interference effects to be exhibited by angular-differential cross sections. Here, we apply the first-order molecular target continuum distorted-wave approximation. Within the distorted-wave formalism, the one-active-electron model, developed to describe collisions with multi-electronic atomic targets, has been employed for the case of $$H_{2}$$ targets. Here, distortion in the final channel related to the Coulomb continuum state of the active electron in the field of residual molecular target ion is included. The present computed results are compared with the available experimental and other theoretical results. The total cross section is obtained by integrating over the projectile’s scattering angle and averaging over all the molecular orientations. The total capture cross sections for all the projectile ions have fair agreement with the experimental observations particularly at lower projectile energies. We have studied the differential cross sections at $$\theta _{\rho }=90^{\circ }$$, $$\phi _{\rho }=0^{\circ }$$, where $$\theta _{\rho }$$ and $$\phi _{\rho }$$ are the polar and azimuthal angles, respectively, of the molecular axis with respect to the incident direction at different impact energies. The interference between two capture amplitudes associated with two centers in the molecule has been found to be more pronounced at fixed orientation of the molecule.

The three-Coulomb wave model has been used extensively to study the energy and angular distributions of double-differential cross sections (DDCS) of electron emissions from hydrogen and nitrogen molecules by bare ion impact at intermediate and high energies. In the present model, we have expressed the molecular triple differential cross section in terms of the corresponding atomic triple differential cross section multiplied by the occupation number and the average Rayleigh interference factor, which accounts for the two-center interference effect. Here we have used an active electron approximation of the molecule as a whole in the initial channel. To account for the effect of passive electrons, we have constructed a model potential that satisfies the initial conditions and the corresponding wavefunction has been calculated from the model Hamiltonian of the active electron in the target. In the final channel, we have used a hydrogenic model with an effective nuclear charge that is calculated from its binding energy. In this model, the correlated motion of the particles in the exit channel of the reaction is considered by an adequate product of three-Coulomb functions. The emitted electron, the incident projectile ion and the residual ion are considered to be in same plane. The obtained results are compared with other recent theoretical and experimental findings. There is an overall agreement of the calculations with the experimental data for electron emission cross sections.

Total cross sections for single charge transfer in collisions of multicharged bare ions with ground-state helium atoms at incident energy ranging from 40 to 5000 keV/amu have been calculated in the framework of a four-body model of final channel distorted-wave (FC-DW-4B) approximation. In this formalism, distortion in the final channel related to the Coulomb continuum of the target and the Coulomb interaction between the passive electron in the target with the projectile are included. In all cases, total single electron-capture cross sections have been calculated by summing over all contributions up to $n=3$ shells and subshells. It has been observed that the contribution of the capture cross sections into excited states have insignificant contributions for symmetric collisions. Comprehensive comparisons are made between the four body model of boundary corrected continuum intermediate-state approximations [Phys. Rev. A 83, 032706 (2011)] and the present FC-DW-4B model. The main purpose of the present study is to investigate the relative importance of dynamic electron correlation and the role of passive electron in the target at intermediate and high impact energies. In addition, projectile angular differential cross sections (DCS) for charge transfer and transfer-excitation in $p\text{-He}$ collisions are calculated at different impact energies. At low projectile energies, the present DCS data exhibits the typical steeply decreasing dependence on the projectile scattering angles, whereas at high impact energies, the double-scattering region centered on the Thomas angle is obtained. Detailed comparisons with the available experimental data and other theories are reported with the purpose of further assessing the relevance of the present model at different impact energies. Overall, the calculated cross sections show good agreement with the available experimental findings.

A theoretical study of double-differential cross sections (DDCSs) for single ionization of ${\text{CH}}_{{}_{4}}$ and ${\text{NH}}_{{}_{3}}$ molecules by collision with proton is presented at 0.25, 1, and 2 MeV, respectively. For the final state, we use a continuum distorted wave that contains the product of three-Coulomb distortion due to pairwise Coulombic interactions for which it is called the three-Coulomb wave model. In the entrance channel, the Coulomb distortion between the incoming projectile and the target is taken. In this model, the ground state of the polyatomic molecule is described by means of an accurate one-center molecular wave function, which is a linear combination of atomic orbitals. The contributions of DDCSs for different molecular orbitals of the polyatomic molecules to the spectrum of angular distributions at different electron emission energies have also been analyzed. Generally the preference for ionization depends on the binding energy of the active electron in molecular orbital in the ascending order of loosely bound electrons to more tightly bound electrons. At large ejected electron and projectile energy, the lesser bound electrons in the molecules dominate the DDCS at extreme forward emission angles. The present DDCS results are compared with available experimental and the theoretical findings. In case of ammonia molecules, good agreement is observed at all projectile energies, showing that the present model is sufficient to explain all the experimental data for double-differential cross sections. However, some degree of discrepancy is observed at 2 MeV proton impact for small electron emission angles when ${\text{CH}}_{{}_{4}}$ molecular target is considered.

Theoretical total cross sections for the double charge transfer in proton-helium collisions are analysed using the four-body boundary corrected continuum intermediate state approximation in the energy range of 30 to 500 keV. We have also obtained differential double capture cross sections as a functions of projectile scattering angle. The intermediate continuum state of each of the active electron has been taken into account in this formalism. Our calculated results are compared with the previous experimental and theoretical values. The agreement is very encouraging.

We have calculated the electron excitation cross sections of hydrogen atom by the impact of protons, alpha particles and He+ ions using the boundary corrected continuum intermediate state approximation in the intermediate and high energies. The calculated results are compared with other theoretical and experimental results. The angular influence of excitation to the H atom at the intermediate energy is also discussed. The distortion effects due to the projectile charges in reactions of electron excitation to bound states of the target H atom are shown in the intermediate and high collision energy.

Post form of “boundary corrected continuum intermediate state (BCIS)” approximation has been employed to study charge transfer cross-sections in collision of Cq+, Nq+ and Oq+ (q=1–5) with ground state atomic hydrogen in the energy range of 50–200 keV/amu. In this formalism we have adopted model potential for the interaction of the active electron with the projectile ion. Calculated results for total charge transfer cross-sections have significant improvement over other existing theoretical results in their comparison to the available experimental findings except for singly charge ions. Sub-shell distribution for total charge transfer cross-section has also been reported in graphical form. Predictions suggested by Olson in connection with the sub-shell distribution of total charge transfer cross-section has been reaffirmed. However, an oscillatory structure of charge state dependence of the total charge transfer cross-sections has not been found in the present investigation.

The classical trajectory Monte Carlo (CTMC) simulation method has been employed to study the sub-shell distributions of total charge transfer cross sections and total ionization cross sections in collisions of partially stripped ions of carbon, nitrogen and oxygen in different charge states (q ≤ 5) with ground state atomic hydrogen in the energy range 10-200 keV amu-1. The total cross section for charge transfer and ionization has been found to be in good agreement with the experimental observations as well as with other theoretical findings. Due to the non-availability of any other experimental results for sub-shell distributions of charge transfer cross sections, comparisons have been made with other existing theoretical results. The observations have been found to be satisfactory. However, an oscillatory structure of the charge-state dependence of the total cross sections has not been found in our calculation.

Charge-transfer cross sections into different subshells of ${\mathrm{C}}^{q+},$ ${\mathrm{N}}^{q+},$ and ${\mathrm{O}}^{q+}$ $(q=1\char21{}5)$ from atomic hydrogen in the ground state have been calculated in the framework of the boundary corrected continuum intermediate-state approximation in the energy range of 40\char21{}200 keV/amu. Interactions of the active electron with the projectile ion have been approximated by a model potential containing both a long-range Coulomb potential part and a short-range part. Total cross-section results for all the ions are in reasonable agreement with available experimental results. However, oscillatory structure of charge-state dependence of total cross sections has not been found in our calculation.

The Coulomb-Born approximation has been employed to study charge transfer cross sections in the case of collisions of (q = 1-3) and (q = 1-4) with atomic hydrogen in its ground state, respectively, within the energy range of . The interaction of the active electron with the incoming projectile ion has been approximated by a model potential. Cross sections for capture into different sub-shells have been given in tabular form. Computed total capture cross sections compare favourably with existing available results.

We present theoretical results for electron emission in collisions between helium atoms and dressed projectiles at high energies. Double-differential cross sections (DDCSs) as a function of the emitted electron energies and angles are calculated. In our study we have applied the three-body formalism using the three-Coulomb wave (3CW–3B) model. The interaction between the dressed projectile and the active electron in the target has been approximated by a model potential having both a long-range Coulomb potential part and a short-range part. However, the active electron in the target has been treated as hydrogenic. We have also studied the projectile charge state dependence of the DDCS. Our theoretical results are compared with available experimental data as well as other theoretical calculations. The comparison shows a good agreement between the present calculations and the measurements. The obtained results are also compatible with other theoretical findings.

We present the double differential cross sections (DDCSs) for the direct ionization of water molecules by impact of fully stripped helium, carbon and oxygen atoms, respectively. In the present formalism, we have represented the wavefunction in the entrance channel as the product of a plane wave for the projectile and an accurate one-center-molecular wavefunction of the water molecule by Moccia (1964 J. Chem. Phys. 40 2186). In the exit channel, we have expressed the total wavefunction as the product of pair-wise Coulomb wavefunctions among the ejected electron, projectile ion and the residual target ion, respectively. The contributions of DDCSs for five different molecular orbitals of water to the spectrum of angular distributions have been analyzed for several electron emission energies. The present results for DDCSs are compared with existing experimental and theoretical findings. We find an overall good agreement between our calculated results and the experimental findings for electron emission cross sections. In addition, DDCS results for ionization from different orbitals at a few electron emission energies are given in tabular form.

Positronium formation into ground and n=2 levels has been studied in collisions of positrons with atomic hydrogen in the framework of an approximation called the boundary-corrected continuum-intermediate-state (BCCIS) approximation in the energy range of 0.08--2 keV. The conventional continuum-intermediate-state approximation does not satisfy the correct boundary condition. It has been shown that, with a suitable choice of the distorting potential, the boundary condition may be satisfied with a proper account of the intermediate continuum states. It has also been shown that the BCCIS approximation leads to the same transition amplitude as may be derived using the Vainshtein-Presnyakov-Sobelman approximation. The results obtained here are found to be in good agreement when compared with other theoretical results.

Double-charge-transfer cross sections into singly and doubly excited states for collisions of {alpha} particles with helium atoms have been studied in the energy range of 50 to 500 keV/amu. We have also studied the double electron capture cross sections into ground states for collisions of {sup 7}Li{sup 3+} and {sup 10}B{sup 5+} with helium atoms. In our study we have applied the four-body boundary corrected continuum intermediate state approximation. The intermediate continuum states of each electron and static correlations of the electrons have been taken into account in this formalism. Present calculated results for total charge transfer cross sections for the reaction {alpha}+He and Li{sup 3+}+He compare favorably well with the existing experimental and other theoretical predictions. Due to the nonavailability of any theoretical and experimental finding for the reaction B{sup 5+}+He, the energy variation of capture cross sections into the ground state of B{sup 5+} ion has been shown within the same energy range. However, charge transfer cross sections into singly and doubly excited states of He are compared with the available theoretical observations only due to nonavailability of any experimental result. In this case as well, agreement is very encouraging.

Single-electron capture by a bare ion from a helium atom at intermediate and high energies in the framework of four-body distorted wave (DW-4B) approximation in both prior and post form has been considered. In the entrance channel, the initial bound state wave function is distorted by the incoming projectile ion, and the corresponding distortion is related to the Coulomb continuum states of the active electron and the residual target ion in the field of the projectile ion respectively. Continuum states of the active electron and the projectile ion in the field of the residual target ion are also included in the exit channel. It may be mentioned that the effect of dynamic electron correlation is explicitly taken into account through the complete perturbation potential. The total single-electron capture cross sections are obtained by summing over all contributions up to n = 3 shells and sub-shells respectively. In addition, the differential cross sections for alpha particle?helium collision are calculated at impact energies of 60, 150, 300, 450, and 630 keV amu?1, respectively. The cross sections exhibit a monotonically decreasing angular dependence, with clear peak structures around 0.1 to 0.2 mrad being found at low impact energies. The current theoretical results, both in prior and post forms of the transition amplitude for symmetric and asymmetric collision, are compared with the available theoretical and experimental results. Current computed results have been found to be satisfactory in comparison with other theoretical and experimental findings.

The molecular three-Coulomb wave model (M3CW) has been extensively used to study the double-differential ionization cross sections (DDCS) of diatomic molecules by the impact of bare ions at intermediate and high energies. In this model, the distortion of the initial channel by the incoming projectile is also included. The present DDCS results are found to be in good accord both with the experiment of Baran et al 2008 as well as with other theory.

We have extended our earlier investigation on asymmetric collisions in the framework of a modified peaking impulse approximation for the case of collisions of fully stripped ions of helium and lithium with carbon and neon. As the charge of the projectile is high, we propose to find an exact estimate of the contribution of charge transfer into higher excited states of the projectile. The contribution of charge transfer into {ital n}=2 states is never found to exceed 12% in the entire energy region of 0.3--3.0 MeV/amu. Total cross sections compare fairly well with existing experimental results.

Four-body formalism of Boundary Corrected Continuum Intermediate State (BCCIS-4B) approximation is introduced to study the (e, 2e) reaction for Helium targets. The influence of the description of the ejected electron on triple differential cross sections is analyzed.

The total and state-selective cross sections for charge transfer in H++He+, He2++Li2+, He2++He+ and Li3++Li2+ collisions were calculated using the boundary corrected continuum intermediate state approximation with an energy range of 30–2000 keV amu−1. In this model, distortion in the final channel related to the Coulomb continuum states of the projectile ion and the electron in the field of the residual target is included. The sub-shell distribution of total charge transfer cross section has been reported in tabular form. Comparison of the results is made with those of other recent theoretical investigations and experimental findings. The present results are found to be in very good agreement with the available experimental findings.

Because of the growing need of excitation cross-section data of atomic hydrogen by fully stripped heavy ions for the preparation of an atomic database for neutral-beam penetration in large tokamaks, we have calculated these data in the framework of the first-order Born approximation for {ital n}{le}20 in the energy range of 0.1 to 1.5 MeV/amu. The present computed results are found to be in agreement with the existing observed results. From the present calculation it also appears that the contribution from subshells characterized by {ital l}{gt}3 is always less than 2%.

The distorted-wave Born approximation and a CTMC model are employed to provide theoretical estimates of the cross sections for the formation of the positronium negative ion (Ps-) in collisions between positronium (Ps) and atomic hydrogen or helium, in the energy range 27 to 170 eV. In the calculation, a previously developed one-electron approach is employed to describe the Ps- ion, and a similar model is also used to describe helium targets.

Charge-transfer cross sections from the ground state of atomic hydrogen into the final 1s, 2s, 2p, 3s, 3p, and 3d excited states of the Li/sup 2 +/ ion by the impact of fully stripped lithium ions are calculated in the Coulomb-Born and Born approximations. The results for the total charge-transfer cross sections are compared with the existing experimental findings and other theoretical calculations. The present calculated results obtained by the Coulomb-Born approximation are found to be in excellent agreement with the experimental results throughout the energy region considered, except in the low-energy region E

A method for the calculation of cross sections for electron capture into arbitrary $n$, $l$, and $m$ states of fast bare projectiles in collisions with fully stripped ions and ground-state hydrogenic targets has been proposed in the framework of the continuum distorted-wave approximation. The charge-exchange amplitude has been reduced to a one-dimensional integral in real space which is very convenient for numerical evaluation. The present method is applied in ${\mathrm{Li}}^{3+}$-$\mathrm{H}(1s)$ collisions and the calculated cross sections are in excellent agreement with the experimental data for the incident energies $E\ensuremath{\ge}700$ keV.

A new straightforward technique for the evaluation of the rearrangement-scattering amplitude for the process H/sup +/+H(1s)..-->..H(nlm)+H/sup +/ has been presented in the continuum--intermediate-state approximation. We reduce the scattering amplitude to a closed analytical form. The asymptotic behavior of the capture cross sections with respect to n has also been derived. It has been shown conclusively that the charge-exchange cross sections asymptotically obey the n/sup -3/ power law throughout the entire energy range of the projectile. It is found that the cross sections for capture into different angular momentum states can be calculated from the respective asymptotic cross-section values with the help of a simple scaling law. The present calculated results have been compared with the available experimental findings.

First theoretical estimates of cross sections for capture and detachment in collisions between protons and negative positronium ions are reported in the energy range 1-100 keV lab for the incident proton. Cross sections have been obtained for a one-active-electron model of Ps- introducing an effective potential for interactions between the outer electron and the positronium core in the system. In the authors calculations, they have applied the semiclassical (impact parameter) formalism using a two-centre atomic orbital expansion with 22 states. In order to test the effective potentials, the authors have computed the photodetachment of Ps- and found that the present approximation is more accurate than the zero-range asymptotic model of Bhatia and Drachman (1985) for incident light with lambda >10*103 AA. A brief discussion of some further approximations made in this work is also given.

The differential cross sections for the excitation of helium atoms to the n=2 level are calculated in the high-energy region by applying the Coulomb-projected Born approximation as proposed by Geltman (1971). Good agreement in the angular distribution is obtained with recently published data.

A new straightforward technique for the calculation of cross sections for electron capture by structureless ions into arbitrary n, l, and m states from the ground state of hydrogenic targets has been presented in the framework of the continuum–intermediate state approximation. We reduce the scattering amplitude to a closed analytical form. We apply this method for the nonsymmetric process H+ + He+(1s) → H(1s, 2s, 2p, 3s, 3p, 3d) + He2+ in the laboratory energy range 50–10 000 keV. Our calculated results are compared with experimental data and existing theoretical calculations.

Cross sections for electron capture by fully stripped ions of berrylium, boron, carbon, nitrogen, and oxygen from ground-state atomic hydrogen have been calculated by applying the previously reported generalized formulation in the continuum intermediate-state approximation. The calculated results are compared with the existing available experimental and theoretical results.

We report semiclassical (impact-parameter) and classical cross sections for antihydrogen formation in collisions between antiprotons p and positronium atoms Ps computed in the intermediate energy range 2–100 keV lab for antiprotons.

Charge-transfer cross sections in collisions of completely stripped ions of boron and carbon with the groun state of atomic hydrogen havve been calculated in the framework of continuum-distorted-wave approximation. The total charge-transfer cross sections have also been evaluated by applying n/sup -3/ law from n = 6 levels. The present calculated results for total cross sections are found to be in better agreement with the experimental results as compared to the existing theoretical results over the entire energy region considered.

Cross sections for double-electron capture from helium atoms by fully stripped ions of lithium, carbon, and oxygen are calculated in the framework of the continuum distorted-wave (CDW) and continuum intermediate-state (CIS) approximations in the energy range of 0.125--2.5 MeV/amu. Cross sections are also calculated for ..cap alpha.. particles as the projectile in the CIS approximation. The results are compared with existing experimental findings. The present calculated results for symmetric and near-symmetric cases show good agreement with the experimental findings. The discrepancies between the calculated and observed values for the asymmetric cases are discussed.

We present cross sections for the formation of antihydrogen, \(\overline H \), and the destruction of the positronium atom, Ps, in collisions between antiproton \(\overline P\) and the positronium target: $$\overline P \; + \;ps\left( {ls} \right)\; \to \;\overline H \left( {n\ell m} \right)\; + \;{e^ - }$$ (1) $$\overline P \; + \;ps\left( {ls} \right)\; \to \;\overline P \; + \;{e^ + }\; + \;{e^ - }$$ (2) in the energy range 2 < E < 100 keV lab (E is impact energy in the laboratory system where the positronium target is assumed at rest) . Reaction (1) is of particular interest because it can be used (1) for production of antihydrogen in a laboratory, provided that cross sections for (1) are not too small at impact energies of few keV (lab).

In the distorted-wave formalism we have proposed a modification in the peaking-impulse approximation suitable for asymmetric collisions. Using this method we have calculated the charge-transfer cross section for K-K capture in collisions of protons with carbon, nitrogen, oxygen, neon, and argon in the energy range of 0.15--20.0 MeV. The present modified peaking-impulse approximation, amenable to exact calculations for the transition amplitude, reproduces results in favorable agreement with observed data and existing theoretical results.