The interaction of a scattering electron with a correlated but ‘‘frozen’’ target may be called the correlated static-exchange interaction. There are two prior investigations [J.R. Rumble, W.J. Stevens, and D. Truhlar, J. Phys. B 17, 3151 (1984); C Weatherford, F.B. Brown, and A. Temkin, Phys. Rev. A 35, 4561 (1987)] on scattering off the correlated static-exchange potential. Both of these investigations concentrated on ${\mathit{e}}^{\mathrm{-}}$+${\mathrm{N}}_2$ scattering, and both have found that the correlated static-exchange potential is less attractive than the static-exchange potential. We will show, however, that the correlated static-exchange potential is more attractive than the static-exchange one—at least for ${\mathit{e}}^{\mathrm{-}}$+${\mathrm{N}}_2$ scattering in ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$ symmetry. The two prior investigations were misled by an improper degree of correlation and by an improper treatment of the exchange.

A quantitative analysis of the influence of small-angle multiple scattering on fast molecules dissociating in solids is made using a Monte Carlo technique. Simulations allow the computation of asymptotic velocities of all of the fragments after Coulomb explosion. It is found that only the simultaneous treatment of the Coulomb explosion and the multiple scattering leads to satisfactory agreement of the simulations with experimental data. Limits on the range of validity for Coulomb-explosion-imaging experiments are determined. It is shown that these limits are ample to allow quantitative spectroscopic data to be extracted from such experiments.

The charge-transfer rate coefficient of ${\mathrm{Mo}}^{6+}$ and argon has been measured at mean ion energies of 8.8 and 1.4 eV using a laser-ablation ion source and an ion trap. The rate coefficient deduced from these measurements is 1.02(0.10)×${10}^{\mathrm{-}10}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$ and appears to be independent of the mean ion energy at this energy range. However, the measured value is an order of magnitude smaller than the Langevin rate coefficient.

Potentials providing the same phase shifts as a given potential, but possibly different bound spectra, are constructed by successive supersymmetric transformations. Three situations are considered: suppression of several lowest bound states, addition of a number of bound states below the ground state, and no modification to the bound spectrum. Compact formulas involving physical or nonphysical solutions of the initial Schrödinger equation are established for the phase-equivalent potentials as well as for their bound or free wave functions. Such expressions, referring only to the initial problem, allow a comparison with other methods. The unchanged-spectrum case is shown to be a combination of the other two; it leads to a well-known result of inverse scattering. A general technique of classification of potentials arising from supersymmetry transformations is proposed. The method is illustrated by the Coulomb potential example, for which elementary analytical forms exist for the phase-equivalent potentials.

The potential-energy curves and the radial coupling matrix elements of the ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }$ states involved in the collision of the metastable ${\mathrm{N}}^{5+}$(1s2s) ${}_{}{}^3{}_{}{}^{}$S multicharged ion on a helium target have been calculated by means of an ab initio method with configuration interaction. The partial cross sections of capture on the 3l levels have been determined using a semiclassical method and compared with experiment. The transfer-excitation process has been considered.

Angular distributions of Auger electrons ejected in 60-keV ${\mathrm{C}}^{6+}$+He collisions were measured. This study extends previous work where cross sections for the production of the configuration 2lnl’ (n≥3) have been determined from measurements at the observation angle of 0° only. For n=3 and 4, the present angular distributions were measured to be anisotropic, whereas for n=5 and 6 the electron emissions were found to be isotropic within the experimental uncertainties. The integration over the observation angle yields total production cross sections ${\mathrm{\sigma }}_{2\mathit{l}\mathit{n}\mathit{l}}$ that were found to follow an ${\mathit{n}}^{\mathrm{-}3}$ law, in agreement with previous calculations. The observed angular distributions are discussed in terms of different capture mechanisms.

Spin-labeling techniques, specifically the use of electron-spin-polarized He(2 ${}_{}{}^3{}_{}{}^{}$S) metastable atoms coupled with energy-resolved spin analysis of the product electrons, are used to investigate the dynamics of Penning ionization in collisions involving He(2 ${}_{}{}^3{}_{}{}^{}$S) atoms. Results obtained using ${\mathrm{CO}}_2$, CO, ${\mathrm{Cl}}_2$, and ${\mathrm{O}}_2$ target gases are presented that illustrate the capabilities of this approach. In particular, the data for ${\mathrm{Cl}}_2$ and ${\mathrm{O}}_2$ confirm that ionization via ionic channels is important and show that exchange and spin-orbit effects must be considered.

In this paper we present the total cross sections for the positron-impact ionization of Na in the range 8–30 eV of the energy of the incident positron. Calculations are done by using a distorted-wave approximation incorporating the effects of screening and distortion. The present results are compared with the experimental results for the electron-impact ionization of Na.

Distortion effects observed in soft-x-ray spectra in the 0.1–5-keV range obtained with xenon gaseous detectors are investigated using a detailed Monte Carlo simulation of the absorption of low-energy x-ray photons in xenon at p=760 Torr and T=293 K, for uniform applied electric fields 100, 500, 1000, 1500, 2000, and 2500 V/cm. Distortion effects are shown to correspond to a loss of electrons to the xenon-filled detector’s window, and the influence of the field strength applied in the detector’s x-ray-absorption zone is assessed.

Various photon emissions from collisions of ${\mathrm{H}}^{+}$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{He}}^{+}$ in the 100–350-keV energy range with targets of CO, ${\mathrm{CF}}_4$, and ${\mathrm{CH}}_4$ were studied. The wavelength range of the investigation ran from 2000 to 7000 Å. Photon-emission cross sections were measured for all significant features. The cross-section data were compared to the Bethe-Born theory through the use of Fano plots. The results show that the theory could be applicable in the case of the CO target, but is probably not applicable to the tetrahedral molecular targets as the emissions are from dissociated atoms.

Separable approximations have been used in electron-molecule scattering calculations to avoid the computation of two-electron matrix elements involving continuum functions. We show that such matrix elements involving one continuum function (proportional to a spherical Bessel function at large distances) and three Gaussian functions can be reduced to a single numerical quadrature of an integral involving ordinary two-election integrals over only Gaussian functions. Using these integrals in the Kohn variational method for electron-molecule scattering allows one to avoid the limitations of a primitive separable approximation for exchange interactions by replacing it with a more stable Schwinger separable expansion. The procedure is demonstrated for electron scattering from the 2 ${}_{}{}^3{}_{}{}^{}$S state of helium.

We discuss the multiplicity distribution of electron-positron pairs created in the strong electromagnetic fields of ultrarelativistic heavy-ion transits. Based on nonperturbative expressions for the N-pair creation amplitudes, the Poisson distribution is derived by neglecting interference terms. The source of unitarity violation is identified in the vacuum-to-vacuum amplitude, and a perturbative expression for the mean number of pairs is given.

Absolute cross sections for electron-impact ionization of ${\mathrm{Cl}}^{+}$ have been measured from threshold to 200 eV with the use of the crossed-beams technique. The cross section shows a peak value of 12.8×${10}^{\mathrm{-}17}$ ${\mathrm{cm}}^2$ at about 70 eV. Results are compared to the semiempirical prediction formula of Lotz, with scaled cross sections for ions in the same isoelectronic sequence, and with other recent measurements. Expansion coefficients and formulas for generating ionization rate coefficients in the electron temperature range ${10}^4$≤T≤${10}^7$ K are presented.

Cross sections differential in the scattering angle of the projectile are presented for electron capture summed over all states and to the 2s, 2p, 3s, 3p, 4s, and 4p states of hydrogen in 25-, 50-, and 100-keV proton-helium collisions. The classical-trajectory Monte Carlo (CTMC) technique was employed for these calculations as well as to compute total cross sections as a function of impact energy. The latter are compared with experiment to display the behavior of the integral state-selective cross sections in this energy regime. Detailed comparison is also made between the calculated angular differential cross sections and the experimental measurements of Martin et al. [Phys. Rev. A 23, 285 (1981)] for capture summed over all states and of Seely et al. [Phys. Rev. A 45, R1287 (1992)] for capture to the 2p state. Very good overall agreement is found. Regarding the cross section for capture summed over all states, an improved agreement is demonstrated by using an alternate representation of the initial state in the CTMC method, which improves the electronic radial distribution but which cannot presently be applied to state-selective determinations.

Single-ionization cross sections of the proton-hydrogen molecule collision are calculated in semiclassical approximation by using atomic and Heitler-London-like two-center molecular wave functions for the ground state of ${\mathrm{H}}_2$. In transition matrix elements, calculated with two-center wave functions, the factors depending on ‖r-${\mathbf{R}}_0$/2‖ (${\mathbf{R}}_0$ is the vector of the molecular axis) are expanded into Legendre series. The calculated total and differential cross sections are compared to the measured data, and their dependence on target wave functions is discussed. The success of the simple approach, which uses twice the cross sections calculated for the hydrogen atom, is explained with the dominance of monopole contributions in the expansion in ${\mathbf{R}}_0$. While for homonuclear diatomic molecules the differential cross sections could be well described by the additivity rule, for other molecules the validity of such approaches is questionable.

Cross sections for double ionization and ionization plus excitation of ${\mathrm{H}}_2$ by high-energy protons are calculated as a function of the orientation of the ${\mathrm{H}}_2$ internuclear axis. Only the contributions of the double-collision process have been included. The ground state of ${\mathrm{H}}_2$ is described by Heitler-London-type wave functions, and the molecular orbitals for the excited states of ${\mathrm{H}}_2^{+}$ are constructed from atomic functions. The results have been compared with the data of Edwards et al. [Phys. Rev. A 42, 1367 (1990); 44, 797 (1991); Nucl. Instrum. Methods Phys. Res. B 53, 472 (1991)] and Ezell et al. [Nucl. Instrum. Methods Phys. Res. B 56/57, 292 (1991)]. The theoretical and measured cross sections have the same magnitude for double ionization. For the excitation of the 2p${\mathrm{\sigma }}_{\mathit{u}}$, 2p${\mathrm{\pi }}_{\mathit{u}}$, and 2s${\mathrm{\sigma }}_{\mathit{g}}$ states, the calculated cross sections are much lower than the measured ones.

Negative-ion and electron yields for collisions of positive alkali-metal ions with a gas-covered heterogeneous molybdenum surface have been measured for impact energies ranging from below threshold up to 300 eV. It is observed that the threshold energies are identical for the sputtering of negative ions and the emission of secondary electrons. The sputtered negative ions are found to be predominantly ${\mathrm{O}}_2^{\mathrm{-}}$ for collision energies in the near-threshold region. It is suggested that near threshold the mechanism for secondary-electron emission involves sputtering an unstable negative ion which subsequently decays, producing a free electron.

Rotationally resolved zero-kinetic-energy (ZEKE) photoelectron spectra of the X ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$(${\mathrm{v}}^{+}$=0,1) ←X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$(v=0) bands of nitrogen have been recorded. The spectra show unexpected rotational-line intensities. The intensity distortions are explained by channel interactions. The strong S and U branches [(${\mathit{N}}^{+}$-J’’)=+2 and +4, respectively] of the (1-0) band borrow intensity from a nearly degenerate Rydberg state, converging to an electronic excited state of the ion, by a complex resonance mechanism. Field-induced rotational autoionization is shown to enhance the O branch and M branch [(${\mathit{N}}^{+}$-J’’)=-2 and -4] intensity of the (0-0) band. Recording ZEKE spectra with extraction fields of 10–100 V/cm appears to be an attractive and powerful way of obtaining spectroscopic information on Rydberg states with simultaneously high principal quantum number n and high total-angular-momentum quantum number J.

The rotational line profiles of the v=0 peaks of the outer-valence X and B states in the photoelectron spectrum of ${\mathrm{N}}_2$ have been observed. The line associated with transitions to the X ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$(v=0) state shows a central peak reflecting the ΔN=0 transitions surrounded by pronounced features corresponding to ΔN=±2 and ±4 transitions. The B ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$(v=0) state shows a doublet structure associated with ΔN=±1 transitions and weaker structures corresponding to transitions with ΔN=±3. The assignments are supported and quantified by simulations of the line profiles.

We apply perturbation theory to the hydrogen atom in a magnetic field by means of a recurrence relation for properly chosen moments of the wave function. The method is suitable for both numerical and symbolic computation and allows the treatment of classes of states with common symmetry properties. We derive analytic expressions in terms of the principal quantum number for the perturbation corrections to the energy of the unperturbed states with quantum numbers n-1=‖m‖=l, n-2=‖m‖=l-1, n-2=‖m‖=l, n-3=‖m‖=l-1, and (n-3=‖m‖=l,n-3=‖m‖=l-2) some of which have not been reported before. Disagreements with some previous results are pointed out.