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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.

In this work, we report theoretical electron capture cross sections for single-electron removal from molecules of biological interest and noble gases by bare ion (H+ and He2+) impact at energies ranging from 25 to 10,000 keV/amu. We use a distorted wave (DW) method where the intermediate continuum state of the active electron with the target ion has been taken into account. This method is developed within the framework of the independent electron model taking particular care of the representation of the bound continuum target states. Two different approximations have been considered for molecular targets: molecular representation of the bound-state target wavefunction and Bragg’s additivity rule. The molecular orbital for targets are described within the framework of the complete neglect of differential overlap (CNDO) method based on the linear combination of atomic orbital (LCAO) approximation. Using the DW method, we have also calculated the K-, L- and M- shell electron capture in collisions of bare ions with three noble gases He, Ne, and Ar respectively. Contributions from different molecular orbitals and different shells to the total cross sections (TCS) are studied. The preference of electron capture occurs in accordance as the binding energy of the active electron in molecular orbital and atomic shell. The maximum contributions to TCS for SC comes from the less bound electrons in repetitive orbitals, whereas the tightly bound electrons dominate the TCS at higher projectile energy regime. Variation of TCS with impact energy are compared with the available experimental observation and other theoretical findings. We find that the present theoretical method is satisfactory in both intermediate and high-energy region for molecules as well as noble gas targets to give reliable outcomes compared to other theoretical methods.

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 low-temperature linear-in-T resistivity of ``strange metals,'' such as the metallic state of the cuprate high-temperature superconductors, has long been thought to be associated with a quantum critical point. However, recent transport studies of the cuprates have found this behavior persists over a finite range of overdoping. In this work, we report magnetoresistance and Hall effect results for electron-doped films of the cuprate superconductor ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$ (LCCO) for temperatures from 0.7 to 45 K and magnetic fields up to 65 T. For $x=0.12$ and 0.13, just below the Fermi surface reconstruction (FSR) at $x=0.14$, the normal state in-plane resistivity exhibits a well-known upturn at low temperature. Our new results show that this resistivity upturn is eliminated at high magnetic field and the resistivity becomes linear-in-temperature from \ensuremath{\sim}40 K down to 0.7 K. The magnitude of the linear coefficient scales with Tc and doping, as found previously [K. Jin, Nature(London) 476, 73 (2011), T. Sarkar, Sci. Adv. 5, eaav6753 (2019)] for dopings above the FSR. This striking observation suggests that the strange metal is not confined to a single ``critical point'' in the phase diagram, but rather is a robust universal feature of the metallic ground state of the cuprates.

We report ${[{({\mathrm{LaNiO}}_{3})}_{\mathrm{n}}/{({\mathrm{LaMnO}}_{3})}_{\mathrm{n}}]}_{\mathrm{M}}/{\mathrm{SrTiO}}_{3}(111)$ superlattices [$n=20$, 10, 5, 2, and 1 unit cells (u.c.)] as ``precursor'' heterostructures for a double perovskite ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$. A charge transfer at the ${\mathrm{LaNiO}}_{3}$/${\mathrm{LaMnO}}_{3}$ interfaces and formation of the emergent ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$ phase with ${\mathrm{Ni}}^{2+}$ and ${\mathrm{Mn}}^{4+}$ oxidation states was evidenced by in situ optical ellipsometry and supported by magnetic and Raman measurements. The 10/10 and 5/5 superlattices revealed a complex magnetic behavior with two ferromagnetic phase transitions with ${T}_{\mathrm{C}\text{\ensuremath{-}}\mathrm{low}}=170\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{C}\text{\ensuremath{-}}\mathrm{high}}\ensuremath{\sim}250--280\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, originating from the ferromagnetic ${\mathrm{LaMnO}}_{3}$ and the emergent interfacial ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$ phase, respectively. With decreasing thickness of individual layers, the magnetism of 2/2 and 1/1 superlattices transforms into that of the ordered double perovskite ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$. Furthermore, a structural reconstruction into a monoclinic $({P}_{12})$ structure of the ordered ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$ at the interface, evidenced by Raman spectroscopy, goes ahead with the charge transfer and magnetic ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$ behavior.

A large 4$\pi$ array of charged particle detectors has been developed at Variable Energy Cyclotron Centre to facilitate high resolution charged particle reaction and spectroscopy studies by detecting event-by-event the charged reaction products emitted in heavy ion reactions at energy $\sim$ 10-60 MeV/A. The forward part ($\theta \sim \pm $ $7^{0}$ - $\pm 45^{0}$) of the array consists of 24 highly granular, high resolution charged particle telescopes, each of which is made by three layers [single sided silicon strip($\Delta$E) + double sided silicon strip (E/$\Delta$E) + CsI(Tl)(E)]of detectors. The backward part of the array consists of 112 CsI(Tl) detectors which are capable of detecting primarily the light charged particles (Z $\le$ 2) emitted in the angular range of $\theta \sim \pm $ $45^{0}$ - $\pm 175^{0}$. The extreme forward part of the array ($\theta \sim \pm $ $3^{0}$ - $\pm 7^{0}$) is made up of 32 slow-fast plastic phoswich detectors that are capable of detecting light (Z $\le$2) and heavy charged particles (3 $\le$ Z $\lesssim$ 20) as well as handling high count rates. The design, construction and characterization of the array has been described., Comment: Paper has been submitted in NIMA

The cuprate high-temperature superconductors (HTSC) have been the subject of intense study for more than 30 years with no consensus yet on the underlying mechanism of the superconductivity. Conventional wisdom dictates that the mysterious and extraordinary properties of the cuprates arise from doping a strongly correlated antiferromagnetic (AFM) insulator (1,2). The highly overdoped cuprates$-$those beyond the dome of superconductivity (SC)--are considered to be conventional Fermi liquid metals (3). Here, we report the emergence of itinerant ferromagnetic order (FM) below 4K for doping beyond the SC dome in electron-doped La$_{2-x} $Ce$_x$CuO$_4$ (LCCO). The existence of this FM order is evidenced by negative, anisotopic and hysteretic magnetoresistance, hysteretic magnetization, and the polar Kerr effect, all of which are standard signatures of itinerant FM in metals (4,5). This surprising new result suggests that the overdoped cuprates are also influenced by electron correlations and the physics is much richer than that of a conventional Fermi liquid metal., Significantly updated version

Energy spectra of light charged particles emitted in the reaction $p + {}^{27}\mathrm{Al} \rightarrow {}^{28}\mathrm{Si}^{\ast}$ have been studied and compared with statistical model calculation. Unlike 16O + 12C where a large deformation was observed in 28Si*, the energy spectra of $\alpha$ -particles were well explained by the statistical model calculation with standard “deformability parameters” obtained using the rotating liquid drop model. It seems that the $\alpha$ -clustering in the entrance channel causes extra deformation in 28Si* in the case of 16O + 12C, but the reanalysis of other published data shows that there are several cases where extra deformation was observed for composites produced via non- $\alpha$ -cluster entrance channels also. An empirical relation was found between mass-asymmetry in the entrance channel and deformation, which indicates that along with $\alpha$ -clustering, mass-asymmetry may also affect the emission of a light charged particle.

We report a systematic study of the Nernst effect in films of the electron-doped cuprate superconductor $\mathrm{L}{\mathrm{a}}_{2\ensuremath{-}x}\mathrm{C}{\mathrm{e}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ as a function of temperature and magnetic field (up to 14 T) over a range of doping from underdoped ($x=0.08$) to overdoped ($x=0.16$). We have determined the characteristic field scale ${H}_{C2}^{*}$ of superconducting fluctuation which is found to track the domelike dependence of superconductivity (${T}_{C}$). The fall of ${H}_{C2}^{*}$ and ${T}_{C}$ with underdoping is most likely due to the onset of long-range antiferromagnetic order. We also report the temperature onset, ${T}_{\mathrm{onset}}$, of superconducting fluctuations above ${T}_{C}$. For optimally doped $x=0.11{T}_{\mathrm{onset}}$ ($\ensuremath{\cong}39\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) is high compared to ${T}_{C}$ (26 K). For higher doping ${T}_{\mathrm{onset}}$ decreases and tends to zero along with the critical temperature at the end of the superconducting dome. The superconducting gap closely tracks ${H}_{C2}^{*}$ measured from the temperature- and field-dependent Nernst signal.

In the physics of condensed matter, quantum critical phenomena and unconventional superconductivity are two major themes. In electron doped cuprates, the low upper critical field allows one to study the putative QCP at low temperature and to understand its connection to the long standing problem of the origin of the high Tc superconductivity. Here we present measurements of the low temperature normal state thermopower (S) of the electron-doped cuprate superconductor La2-xCexCuO4 (LCCO) from x=0.11 to 0.19. We observe quantum critical S divided by T versus ln(1/T) behavior over an unexpectedly wide doping range x = 0.15 - 0.17 above the putative QCP (x=0.14) with a slope that scales monotonically with the superconducting transition temperature. The presence of quantum criticality over a wide doping range provides a new window on the criticality. The thermopower behavior also suggests that the critical fluctuations are linked with Tc. Above the superconductivity dome, at x=0.19, a conventional Fermi liquid S proportional to T behavior is found for T less than equal to 40 K., Comment: 16 pages, 5 figures

An understanding of the normal state in the high-temperature superconducting cuprates is crucial to the ultimate understanding of the long-standing problem of the origin of the superconductivity itself. This so-called strange metal state is thought to be associated with a quantum critical point (QCP) hidden beneath the superconductivity(1,2). In electron-doped cuprates in contrast to hole-doped cuprates it is possible to access the normal state at very low temperatures and low magnetic fields to study this putative QCP and to probe the T~0 K state of these materials(3,4). We report measurements of the low temperature normal state magnetoresistance (MR) of the n-type cuprate system La2-xCexCuO4 (LCCO) and find that it is characterized by a linear-in-field behavior, which follows a scaling relation with applied field and temperature, for doping (x) above the putative QCP (x= 0.14)(5). This unconventional behavior suggests that magnetic fields probe the same physics that gives rise to the anomalous low-temperature linear-in-T resistivity(4). The magnitude of the linear MR decreases as Tc decreases and goes to zero at the end of the superconducting dome (x ~0.175) above which a conventional quadratic MR is found. These results show that there is a strong correlation between the quantum critical excitations of the strange metal state and the high-Tc superconductivity., Comment: 21 pages, 13 figures, comments are welcome

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.

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.

We consider here a model of the spherical void (or its precursor) containing low density conducting fluid surrounded by a thick spherical shell of radiation embedded in a RobertsonWalker (RW) universe with flat space sections. The underdense region has a metric which is the special case of a solution given by Maiti [1] surrounded by Vaidya metric. We also assume the RW universe to be filled with a perfect fluid with a linear equation of state. The matching conditions indicate that if the time coordinate in each region is future directed then the underdense region appears to go on contracting to a comoving observer in the universe as the latter expands until it disappears. However, if the pressure in the RW universe vanishes, (approximately the present day condition), the underdense region remains static. We have also extended the space-time coordinates of Vaidya metric to the interior of the underdense region as well as the RW universe. It remains to be seen if the region having Vaidya metric disappears earlier than the interior or vice versa.

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.

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.

The authors have set up the Klein-Gordon equation in the background of the Schwarzschild curved space-time and studied the scattering of radial tardyons and tachyons from a black hole. They also show that black holes of mass below 7*1014 g may contain bound states of tardyons of pion mass which will be unstable on account of the presence of an attractive r-4 term.

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.