Search

We have investigated the process of single-electron transfer from the H atoms to the incident Si3 + in the low energy region (0.1 ≤ E ≤ 5.0 keV/u) to determine the significance of additional electronic states of (SiH)3 + and rotational coupling matrix elements. Total and state-selective cross sections are calculated using both quantal and semiclassical molecular-orbital close-coupling (MOCC) approaches based on the molecular state expansion in the adiabatic representation (adiabatic MOCC). A detailed comparison of quantal and semiclassical transition probabilities is reported. The multireference single- and double-excitation configuration interaction (MRD-CI) method is employed to evaluate the adiabatic potentials and nonadiabatic coupling matrix elements of the system. When compared with other theoretical results, our total MOCC cross sections show good agreement with experimental results. At higher energies our results agree nicely with the findings of electron nuclear dynamics (END) calculations.

The differential, integrated elastic, momentum transfer, viscosity and total cross-sections along with Sherman function for the elastic scattering of electrons and positrons by sodium atoms...

The Sternglass theory [Sternglass, Phys. Rev. 108, (1957) 1] for fast-ion-induced secondary-electron emission, which is proportional to the stopping powers, from metals has been modified to calculate the electron impact secondary electron yield from both elemental and compound targets with atomic number Z = 4–92 for incident energy range 5 ≤ E i ≤ 10 5 eV . This modification includes the use of a realistic stopping power expression that involves calculations of the effective atomic electron number, effective mean excitation energies and realistic electron density distribution of the target atoms along with the effective charge of incident electron. Throughout the studied energy range, the predictions of our proposed theory are in reasonable agreement with the experimental data for Be to U elemental and six important compound targets.

A simple modification of the Vaisburd and Evdokimov model (VE) [Russ. Phys. J. 46 , 1160 (2003)], with a acronym MVE, embodying the relativistic effects is proposed and employed to evaluate the K -shell ionization cross sections of atomic targets with atomic numbers 6 ≤ Z ≤ 92 for incident energies E Threshold ≤ E ≤ 10 GeV. For a meaningful comparison we also revisited our earlier MUIBED model [Int. J. Q. Chemistry, 108 , 1023 (2008)] to obtain the K -shell ionization cross sections for 24 atomic targets and above mention energy range. It is found that our new results from the MVE model agrees quite well not only with available experimental data but also with other theoretical values.

The differential, integrated elastic, total and momentum transfer cross sections along with Sherman function for the elastic scattering of electrons and positrons by cadmium atoms have been evaluated from the partial wave solution of the Dirac relativistic scattering equations for a projectile-atom complex potential at the energy range 6.4 eV < E < 1.0 keV. For various scattering quantities, a comparison of our results exhibits better agreement with the experimental data than the other available theoretical values.

This paper reports on the differential, integral, momentum transfer and viscosity cross sections along with spin polarisation for elastically scattered electrons and positrons from iron atoms in th...

Stopping cross sections (SCS) for protons, alphas and Li ions are calculated with a modified form of our earlier work by incorporating a different electron density distribution of target materials; this involves four parameters – two projectile dependent and the rest two remain fixed. The prosed model has been tested for three stripped ion (H+, He2 + and Li3 +) projectiles and found that it describes quite satisfactorily the experimental SCS data from low energies with projectile velocities nearing v = Z1v0 (with Z1 as the atomic number and v0 the Bohr velocity) up to 100.0 MeV over a wide range of stopping media with atomic numbers Z2 =3–100.

Calculations of electron-impact ionization cross sections (EIICS) for L -subshell of neutral atoms with atomic number Z = 14–92 and also for M -subshell targets, having atomic number Z = 35–92 for incident energies E threshold ≤ E ≤ 10 6 keV, have been reported. This review comprises the results of our two easy-to-use models, capable of reproducing very closely the experimental EIICS data. We also show systematically how these models can be implemented easily to generate accurate data as demanded by various model applications. The choice of the range of atomic number Z for both L - and M -subshell targets was made possible by the wealth of the EIICS data in literature either from experiments or from rigorous quantal calculations. The detailed findings due to our XMCN and XMUIBED models are compared with the experimental and other theoretical results. Present results describe the experimental data quite well for the L - and M -subshell for various atomic targets over a wider range of projectile energy.

We present an ab initio study of the electronic stopping power of protons in copper over a wide range of proton velocities $v = 0.02-10~\mathrm{a.u.}$ where we take into account non-linear effects. Time-dependent density functional theory coupled with molecular dynamics is used to study electronic excitations produced by energetic protons. A plane-wave pseudopotential scheme is employed to solve the time-dependent Kohn-Sham equations for a moving ion in a periodic crystal. The electronic excitations and the band structure determine the stopping power of the material and alter the interatomic forces for both channeling and off-channeling trajectories. Our off-channeling results are in quantitative agreement with experiments, and at low velocity they unveil a crossover region of superlinear velocity dependence (with a power of $\sim 1.5$) in the velocity range $v = 0.07-0.3~\mathrm{a.u.}$, which we associate to the copper crystalline electronic band structure. The results are rationalized by simple band models connecting two separate regimes. We find that the limit of electronic stopping $v\to 0$ is not as simple as phenomenological models suggest and it plagued by band-structure effects., 8 pages, 7 figures

In this article, we investigate the role of the self-interaction error in the simulation of collisions using time-dependent density functional theory (TDDFT) and Ehrenfest dynamics. We compare many different approximations of the exchange and correlation potential, using as a test system the collision of $\mathrm{H^+ + CH_4}$ at $30~\mathrm{eV}$. We find that semi-local approximations, like PBE, and even hybrid functionals, like B3LYP, produce qualitatively incorrect predictions for the scattering of the proton. This discrepancy appears because the self-interaction error allows the electrons to jump too easily to the proton, leading to radically different forces with respect to the non-self-interacting case. From our results, we conclude that using a functional that is self-interaction free is essential to properly describe charge-transfer collisions between ions and molecules in TDDFT., 9 pages, 8 figures

Charge exchange in collisions of C6+ ions with H and H2 is investigated theoretically at projectile energies 0.1 < E < 10 keV/amu, using electron nuclear dynamics (END) − a semi-classical approximation which not only includes electron translation factors for avoiding spurious couplings but also employs full dynamical trajectories to treat nuclear motions. Both the total and partial cross sections are reported for the collision of C6+ ions with atomic and molecular hydrogen. A comparison with other theoretical and experimental results shows, in general good agreement except at very low energy, considered here. For H2, the one- and two-electron charge exchange cross sections are calculated and compared with other theoretical and experimental results. Small but non-negligible isotope effects are found at the lowest energy studied in the charge transfer of C6+ with H. In low energy region, it is observed that H2 has larger isotope effects than H atom due to the polarizability effect which is larger than the mass effect.

Differential cross sections and spin asymmetries for leptons colliding with light and heavy targets are calculated at collision energies E-e ranging from 1 eV to 0.3 GeV. For 1 eV 1 MeV within the nuclear potential. At E-e > 10 MeV, the phase shift analysis is supplemented with the distorted-wave Born approximation to account for magnetic scattering. As test cases, elastic collisions of e(+/-) with Na-23, Cd-112 and Pb-208 atoms are reported, and good agreement with available experimental data and other theoretical cross sections is obtained. For electrons, pronounced structures in the spin asymmetry occur at low energies and small scattering angles. They disappear beyond 50 keV and reappear beyond 50 MeV, being then particularly strong for spin-zero nuclei at large scattering angles. For positrons, the high-energy diffraction structures are shifted in phase with respect to those in the electron spin asymmetry. The strong reduction of the positron spin asymmetry and the quenching of the structures at low-energy is interpreted in terms of a dominating action of the nuclear potential.

A simple modification of the revised Deutsch–Mark model (RDM) [Deutsch et al., Int J Mass Spectrom 2004, 233, 13] incorporating both the ionic and relativistic corrections is proposed to investigate the K-shell ionization of 30 atomic targets with atomic numbers Z = 1–92 for incident energies up to 2 GeV. We also revisit our earlier models: modified Bell (MBELL) (Haque et al., Phys Rev A 2006, 73, 012708) and modified Kolbenstvedt (MKLV) (Uddin et al., Eur Phys J D 2006, 37, 361), for the K-shell ionization cross sections at these ultra-relativistic energies. The results from the modified version of RDM (MRDM), MBELL, and MKLV models agree well with the available experimental data and quantum mechanical calculations. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

A new semiempirical model comprising few important features of the DM model of Deutsch et al. (Int J Mass Spectrom 1998, 177, 47) and the widely used empirical model of Bell et al. (J Phys Chem Ref Data 1983, 12, 891) has been proposed. The proposed model has been examined to evaluate the electron impact K-shell ionization cross sections of 30 atomic targets ranging from H to U (Z = 1–92) and found to describe with considerable success the experimental results over a wide range of incident energies up to 2 GeV using a single set of species independent parameters. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

We propose an extension of the modified simplified-improved-binary-encounter dipole (MRIBED) model (Uddin et al., Phys Rev A 2005, 72, 032715), incorporating both the ionic and relativistic corrections, to investigate the K-shell ionization of atomic targets with atomic numbers Z = 1 − 92 for incident energies up to 2 GeV. We also revisit our earlier models, MBELL (Haque et al. Phys Rev A 2006, 73, 012708) and MKLV (Uddin et al. Eur Phys J D 2006, 37, 361), for the K-shell ionization at these ultra-relativistic energies. The results from our extended version of MRIBED, MBELL, and MKLV models agree well with the experimental findings. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

The electron impact K-shell ionization (EIKSI) cross sections on 18 atomic targets, with the atomic numbers 2 Z 92, are calculated using a modified version of the binary encounter approximation (BEA) model. The modified BEA (MBEA), which incorporates both ionic and relativistic corrections and is simpler in application than other existing models, is found to be immensely successful in describing the EIKSI data up to the incident energy of 1 GeV. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem 108: 1326 -1333, 2008

Calculations of electron impact ionization cross sections (EIICS) for H to Sc (with atomic number Z =1–21) and their corresponding isoelectronic series over incident energies up to 106 keV have been reviewed. This work reports the results of calculations using our various easy-to-use models reproducing closely the experimental EIICS data. We also report how these models can easily be implemented to generate accurate data as demanded by various model calculations. The selection of the range of atomic number Z for different isoelectronic series was made possible by the wealth of the EIICS data either from experiments or from rigorous quantum calculations. We have furnished the detailed description of our various models with comparison of the outcomes of these models with experimental and other theoretical results. Our models describe the experimental results with reasonable success for various atomic and ionic targets belonging to the H to Sc isoelectronic series over a wide range of atomic number in each series.

The recently modified Kolbenstvedt (MKLV) model [Eur. Phys. J. D 37, 361 (2006)], developed for electron impact ionization (EII) of the K-shell atomic targets, has been extended to generalize its two parameters in terms of the electronic orbitals nl. The generalized MKLV (GKLV) with two sets of the species independent parameters for the same nl, one set for the ionization of inner orbits and another for the outermost orbit, is found profoundly successful in accounting for the EII cross section data of the K, L and M-shell neutral atoms with atomic numbers Z = 1-92 for the incident energies up to 1000 MeV in a consistent manner.

The modified BELL (MBELL) formula (Haque et al 2006 Phys. Rev. A 73 012708) has been applied to the M-shell ionization of neutral and ionic atoms to deduce the `generalized' parameters of the 3s, 3p and 3d orbits. A single set of parameters for each of these orbits and that previously determined for each of 1s, 2s and 2p orbits can reproduce satisfactorily the features of the total electron impact ionization cross-sections (EIICS) of 21 M-shell targets in the Na, Mg, Al, Si, P, S, Cl, Ar and Ca isoelectronic sequences. The generalized parameters are also found to provide an excellent account of the M-shell EIICS data of Pb, Bi and U atoms at relativistic energies in the range from 20 to 250 MeV.

The parameters of our recent modification of BELI formula (MBELL) [A.K.F. Haque, M.A. Uddin, A.K. Basak, K.R. Karim, B.C. Saha, Phys. Rev. A 73 (2006) 012708] are generalized in terms of the orbital quantum numbers nl to evaluate the electron impact ionization (EII) cross sections of a wide range of isoelectronic targets (H to Ne series) and incident energies. For both the open and closed p-shell targets, the present MBELL results with a single parameter set, agree nicely with the experimental cross sections. The relativistic effect of ionization in the 2p subshell of U 82+ for incident energies up to 250 MeV is well accounted for by the prescribed parameters of the model.

The electron impact single ionization cross-sections on the Be, B+, C2+, N3+, O4+, Ne6+, Fe22+ and U88+ atomic targets, in the beryllium isoelectronic sequence (BIS), are calculated using the modified versions of simplified improved binary-encounter dipole model (siBED) [W.M. Huo, Phys. Rev. A 64 (2001) 042719]. The modified models, QIBED (with the ionic correction) and RQIBED (with both the ionic and relativistic corrections) [M.A. Uddin, A.K.F. Haque, A.K. Basak, B.C. Saha, Phys. Rev. A 70 (2004) 032706], are found to provide an excellent description of the experimental data for all the targets in BIS with the same generic values of the two parameters d 1 and d 2 in the models. The RQIBED results describe satisfactorily the assessed data of Be and its predictions for U88+ account for well the experimental K-shell ionization data of Sn, with almost the same properties of the ionized orbit concerned, even up to around 2 MeV.

A standard technique for solving three-dimensional momentum-space integral equations in scattering theory is their transformation into one-dimensional equations in terms of partial waves. However, for some scattering systems where a large number of partial waves contribute this technique is not efficient. In this work we explore the alternative approach of solving these equations directly without partial-wave expansion. For illustrative purposes we adopt the coupled-channel approach and consider a well-studied static-exchange model of electron-hydrogen scattering.

The cross sections for electron-impact single ionization of helium-like targets,—Li+, B3+, C4+, N5+, O6+, Ne8+, Na9+, Fe24+, Ag45+, and U90+—are calculated using a recently propounded parameter-free relativistic binary encounter (RBEA) model, which remains valid up to the relativistic energy domain. Our RBEA results are compared with those of the Coulomb–Born (CB) approximation, distorted wave Born approximation (DWBA), relativistic two-potential DWBA (RTPD), the simple empirical model of Brenshtam et al. (BRY), and the model of Deutsch and Mark (DM) along with the available experimental data. The RBEA model, while keeping the comparable predictive power of cross sections, is found to overcome the limitations of the empirical BRY and DM models with their fitting parameters, and the quantum mechanical CB, DWBA, and RTPD theories with arduous and lengthy calculations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Low-energy state-changing cross sections involving the ground state of He atoms and ground states of Li atoms are calculated using the semiclassical impact parameter close-coupling method based on a molecular states expansion to represent the electronic wave function. The plane wave translation factor is used considering a classical trajectory for the motion of the heavy particles. We approximate this many electrons system to a one-electron problem by using the l-dependent pseudopotential technique. In order to obtain cross sections, we retain nine molecular states including six Σ and three Π states in our close coupling calculations, but, in the structure calculations, we have included 16 states (ten Σ and six Π states) so the excitation of 5s levels of the target Li atoms is possible. Our cross sections for Li (2p) excitation agree well with previous theoretical and available experimental results.

The low-energy single electron capture cross-sections by C6+ from H atoms have been evaluated employing the semiclassical, impact parameter, close-coupling method based on a molecular expansion augmented with the plane-wave translation factor. Using the method of Bates and Carson, the exact Born–Oppenheimer eigenfunctions and eigenvalues are calculated. Eight-state coupled equations are solved to obtain transition probabilities and thereby evaluate capture cross-sections. Our calculated capture cross-sections agree well with other theoretical and experimental results. At these energies it is found that the capture into the n = 4 manifold of the C5+ remains the main contributor to the charge exchange process. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

The spin-polarization S and the spin-polarization parameters U and T of the elastically scattered electrons from Hg atoms have been computed for scattering angles 0°–180° in the energy range 1 eV . An optical model approach is employed using a complex optical potential within the framework of the Dirac relativistic partial wave analysis. We compare our results with recent experiments and available theoretical calculations and find a reasonable agreement with experiments over a wide range of energies.

We report an extension and modification of the MCN model of Haque et al (2013 Rad. Phys. Chem. 91 50–9) (XMCN) to study the electron impact ionization of inner L and M shells of neutral atoms by introducing new parameters of the MCN model. The extended XMCN model, including the relativistic effect, has been applied with success to evaluate ionization cross-sections of various atomic targets with Z = 38–92 for both individual subshells and total L-shell and the corresponding cross-sections for the M shell for Z = 79–92 at incident energies E Threshold 1 GeV. A comparison with other available theoretical and experimental cross-sections reveals that our results reproduce the experimental measurements with a reasonable accuracy.

We report calculations of state-selective electron capture by H+ from K(4p) in Σ and Π alignments, in the 0.01–1 keV/amu energy range. We use, in the impact parameter formalism, the semiclassical close-coupling method with molecular-state expansion embodying electronic translation factors. Molecular states and adiabatic states are obtained from standard one-electron LCAO calculations using Slater-type orbitals and pseudopotentials for the e−–K core interactions. In addition to the state-selective capture cross sections, we also have calculated the K(5s), K(3d), and K(5p) excitation cross sections. We report the anisotropy parameters A(n) for n=2 and n=3 states of the formed H atom as well as A(ex) for populating the excited states of the K atom for the first time. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

The semi-classical, impact parameter, close-coupling method, in its molecular orbital form is employed to investigate the process of state selective charge transfer from a two-electron target (He) to the incident bare nucleus of Li (i.e. Li 3+ ) in the low-energy region. The effective binding of the active electron in the quasi-diatomic molecule formed during the course of collision is obtained for the first time in an ab initio way. The electron translation factor (ETF) modified Born–Oppenheimer wave function is generated to obtain the adiabatic molecular states of the quasi-molecule (LiHe) 3+ . A set of eight close-coupled equations is solved numerically to obtain both the partial and total capture cross-sections at 0.5≤E≤5 keV amu −1 . The cross-sections are compared with both the low-energy measurements and other available theoretical results. The explicit n - and l -distributions of the capture cross-sections are also presented for the first time. Comparison is made with a recent calculation carried out in a similar manner for Li 3+ –H 2 , another two-electron colliding system. The structureless ion of Li, as expected, favors highly state selective population of the Li 2+ (2p) state in this collision.

Low-energy (E≤1 eV) state-changing collisions of excited atom, particularly the low-Rydberg (n 3) propensity rule holds. The explanation lies in the ordering of the relevant adiabatic energy curves and the nature of the coupling. The Stueckelberg interference oscillations are found in the inelastic cross sections. The role of the nonspherical target state before the collision is discussed. The total thermal energy quenching rates are calculated and compared with the experiment results. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 1011–1023, 2000

Single-electron capture cross sections from H 2 by a number of fully and partially stripped ions (2≤ q ≤6) has been calculated using a semi-classical Molecular Orbital approximation. During the course of the collision a transient quasi-molecule comprising the entrance and various exit channels of the charge-transfer reactions is considered. Freezing the molecular details of the target, the effective binding of the active electron inside the transient molecule is simulated employing pseudo-potential. A multi-channel calculation is carried out in which the number of molecular states to be coupled together is decided by the collision dynamics of the individual pair. The calculated cross sections agree very well with the available experimental results. Although the Landau–Zener mechanism is mainly responsible for the observed state-selective charge-exchange process, no generalization in terms of projectile charge or structure is possible to predict the behavior of individual interactions. The total cross sections, along with their l-distribution, for the O 6+ –H 2 system are reported here for the first time.

An improved theory within the frame work of Fermi's Free-Electron model has been proposed to evaluate the Hornbeck Molnar Ionization (HMI) cross sections, and has been applied to investigate the formation of homonuclear alkali diamers at thermal energies. The calculated cross sections for all homonuclear pairs involving Rydberg alkali atoms and the ground state alkali atoms are compared with the available experimental results. In the limit of large n (the principal quantum number of the parent Rydberg atom) present results predict the correct asymptotic behavior but disagree considerably with the earlier findings of Kumar and Gounand [J. Phys. B 20 (1987) 2773].

Total quenching of the low-Rydberg state of Na in collision with thermal Ne and Ar was investigated, for the first time, employing a molecular approach in the impact parameter formalism. A large basis set of Slater-type orbitals was used to calculate the molecular structure of the transient quasimolecule formed during the collision; pseudopotentials were used to incorporate the effective binding of the distant electron. A 14-channel calculation was carried out to evaluate the total depopulation cross sections for Na(9s) colliding with the ground-state Ne and Ar atoms in the thermal-energy region. The two colliding pairs not only differ from each other, but also show wide variations from the previously studied NaHe pair, in terms of details of the collision dynamics. In the case of the NaAr system, a unique feature that leads to appreciably larger quenching cross sections shows qualitative agreement with the measurement. A comparative study of three (He/Ne/ArNa) colliding pairs reveals that the simplified approach like the free-electron model or the impulse approximation fails to provide details of such state-changing reactions. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 307–316, 1999

The low-energy state-selective capture cross sections for single-electron transfer from the ground state of Na(3s) atoms by fully (C{sup 6+} and N{sup 7+}) and partially stripped (C{sup 4+} and N{sup 5+}) ions have been calculated using the semiclassical approximation in the molecular orbital formulation augmented with the proper electron translation factor. The method of pseudopotential is invoked to account for the interaction of the active electron with the moving nuclei, whose relative motion is considered via a straight-line trajectory. Although both C{sup 4+} and N{sup 5+} have identical He-like structure, their roles reveal very different collision dynamics. The projectile C{sup 4+} exhibits a distinctive role due to its finite core; a low-energy structure in the total capture cross section for C{sup 4+} -Na(3s) collisions is observed and explained. For bare projectiles (C{sup 6+} and N{sup 7+}) there remains an increasing tendency of the Stark mixing to characterize the electron transfer processes; it enhances the population of the higher {ell} states. The {ell} distribution of the charge-transfer cross section for various projectile is also discussed.

The semiclassical molecular orbital approximation modified by a proper electron translation factor has been employed to investigate the dynamics of the low-energy charge transfer between molecular hydrogen and a few stripped ions having charges . Freezing the molecular details of the target the colliding system has been treated as a quasi-diatomic molecule using the pseudo-potential technique that accounts for the effective binding of the electron in the combined nuclear field. Close-coupled equations are solved to obtain both the total and partial capture cross sections. The calculated total cross sections show good agreement with the available experimental measurements; the reported -distributions for and are new. A relative comparison for single-electron transfer from by other ions considered reveals the possible role of the projectile core; in the low-energy region the increasing core size affects considerably both the -distribution and the shape of the total capture cross sections. The projectile exhibits a distinctive role due to its finite core; the calculated total cross sections show oscillations in complete agreement with the experimental findings. The presence of a finite core enhanced the contribution to the lower -value substate of the final channel in accordance with the role of the Stark effect; the state-selective capture cross sections depend strongly on the size of the projectile core.

The process of single-electron transfer from ground state Na to the incident ions of and has been investigated theoretically in the low-energy region . Although both and possess identical He-like structure, their roles reveal very different collision dynamics. The semiclassical approximation in the molecular orbital formulation augmented with the proper electron translation factor, has been used to calculate both the partial and the total capture cross sections. A low-energy structure in - Na has been observed, but for - Na collisions the cross section remains a smoothly varying function of the impact energy. The possible underlying mechanism that leads to the low-energy structure in the - Na process is discussed. Present total cross sections are compared with recent CTMC results.

The collisional quenching of excited Na(4p) by He and H{sub 2} has been studied using the semiclassical, impact-parameter, close-coupling method based on a molecular expansion augmented by the plane-wave translation factor. Interactions between the colliding partners are approximated using suitable pseudopotentials. At low velocities 0.0005{le}v{le}0.001thinspa.u., interference oscillations which depend on the spatial alignment of the electron charge distribution before the collision are present in the cross sections for H{sub 2} quenching perturber. The cross sections due to H{sub 2} are larger than those of He atoms throughout the energy region. At T=470thinspK the present quenching rate coefficients show good agreement with the experimental data of Kleiber {ital et al.} [J. Chem. Phys. {bold 98}, 1101 (1993)]. {copyright} {ital 1997} {ital The American Physical Society}

The Schrodinger equation for the scattering of an electron by a hydrogen molecule is solved by the finite element method, in spherical coordinates, using fifth-order Hermite interpolating polynomials. The computational method is quite similar to the work of Shertzer and Botero [Phys. Rev. A 49, 3673 (1994), and references therein]. However, to study large systems, an effective one-particle dynamical equation is defined, unlike the procedure of Shertzer and Botero. To illustrate the basic computational procedure, a model electron–H2 interaction potential (static+exchange+polarization) is constructed and the K-matrix is calculated. A novel feature of the present method is the procedure for extracting the partial-wave amplitudes at a value of r, the size of which is fixed by the range of nonlocal potentials in the problem, and then propagating the scattering amplitudes out to an effective infinity where the converged K-matrix is determined. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 591–600, 1997

Absolute magnitudes of stopping cross sections (SCS) for H+, He2+ and Li3+ in various stopping media with atomic numbers Z 2 = 2 to 100 are calculated using atomic density functions from Dirac-Hartree-Fock-Slater wave functions in the Lindhard-Schraff theory [J. Lindhard, M. Scharff, Kgl. Danske Videnskab. Selskab. Mat. Fys. Medd. 27, 15 (1953)]. The newly proposed formula, characterizing projectile-specific parameters in the incident energy range considered herein, describes satisfactorily the experimental and SRIM-simulated SCS data from low energies, with projectile velocities nearing v = Z 1 v 0 (with Z 1 as the projectile’s atomic number, v 0 = c / 137, the Bohr velocity and c, the speed of light in vacuum), to high energies up to about 2.5 MeV/u.

Charge-transfer cross sections from the initially aligned np-state of alkali atoms by protons have been calculated in the 10 eV to 5 keV amu−1 energy region. The semiclassical impact-parameter method is employed wherein a coupled molecular states expansion, augmented by the plane wave electron translation factor, is used to represent the electronic wave functions. The dependence of the cross section for the formation of the first excited (n = 2l) states of H, on the orbital geometry and the alignment of the initial state, is discussed. The cross sections are sensitive to the variation of the spatial alignment of the electron charge distribution. The cross section decreases with increasing initial alignment at lower energies, and at higher energies, the situation is reversed. At E = 0.05 keV amu−1, the cross section is isotropically aligned. At this energy, the cross section is the same for both the initial states Σ and Π. The orientation of the excited H(2p) orbital resulting from electron capture is also given.

Total and state-selective charge-transfer cross sections for ${\mathrm{C}}^{4+}$-H collisions have been calculated in the energy range 0.02--1.0 keV/amu by employing the semiclassical, impact-parameter, close-coupling method based on a molecular-state description of the ${\mathrm{CH}}^{4+}$ system and including plane-wave translation factors. The calculated cross sections are in good agreement with the quantum calculations as well as with the experimental findings. The integral alignment (${\mathit{A}}_{20}$) parameter for the ${\mathrm{C}}^{3+}$(3p) state is also presented.

A theoretical study of Stueckelberg interference structure in inelastic, state-changing integrated cross sections for collisions of low-Rydberg Na ([ital n][lt]10) atoms with ground state He atoms is reported. The dependence of the Stueckelberg interference structure on orbital geometry and alignment of the initial state is predicted. Interference oscillations are found in the cross sections for both initial [ital ns] and [ital np] states; in the latter case, the features show considerable sensitivity with respect to variations in the spatial alignment of the principal axis of the electron charge distribution at some collision velocities and near isotropy at others.

Electron impact inner-shell ionization cross-section (EIICS) calculations of neutral atoms with atomic numbers Z = 6–92 for K-shell, Z = 18–92 for L-shell, and Z = 79–92 for M-shell have been reviewed. In this work, the evaluations of the EIICS are discussed using our recently propounded easy-to-use models that are found adequately successful in describing the experimental cross sections. The selection of the range of atomic number Z for different inner-shells was guided by the availability of the EIICS data either from experiments or from rigorous quantal calculations. Details of the models have been presented and their findings are compared with the experimental and other theoretical results. Our models describe the experimental results nicely for K-, L-, and M-shell ionization for Z ≤ 92 in the energy range E ≤ 2 GeV.

A comparative study for the electron capture process ${\text{O}}^{+}\text{ }({^{4}S}^{0},{^{2}D}^{0},{^{2}P}^{0})+\text{He}\ensuremath{\rightarrow}\text{O}(^{3}P)+{\text{He}}^{+}$ is reported. The cross sections are calculated using fully quantal and semiclassical molecular-orbital close-coupling (MOCC) approaches in the adiabatic representation. Detailed comparison of transition probabilities and cross sections is made from both MOCC approaches and displays close agreement above $\ensuremath{\sim}125\text{ }\text{eV}/\text{u}$. The remarkable discrepancies between the earlier semiclassical and quantal MOCC approaches may be attributed to the insufficient step-size resolution in their semiclassical calculation [M. Kimura et al., Phys. Rev. A 50, 4854 (1994)]. Our results have also been compared with experiment and found to be in good agreement.