A complete electron-photon polarization-correlation study of the 3 ${}_{}{}^1{}_{}{}^{}$D state of helium excited by 26.5-eV incident electrons is carried out for electron scattering angles in the range 40°–120°. The data are analyzed in terms of the shape and dynamics of the excited-state charge cloud. When the results are considered in the natural coordinate frame, the excitation is dominated by the M=+2 excitation amplitude. The lack of theoretical calculations for S-D excitation processes is this energy regime is highlighted.

Results of close-coupling calculations using the complex Kohn method are reported for excitation of the methane molecule into electronically dissociative states. The excited states in question are of Rydberg nature and are classified by analogy with the isoelectronic Ne atom as 2p→3s, 2p→3p, and 2p→3d transitions, i.e., single excitations of the valence 2p electron into the n=3 Rydberg manifold. On the basis of optical selection rules, one expects large excitation probabilities to analogues of ${}_{}{}^1{}_{}{}^{}$P odd-parity states. Our calculations in the energy range 11–60 eV show a more complex picture of the excitation dynamics and detect large excitation probabilities for triplet and even-parity (2p→3p) states. A similar result is obtained for the excitation of the Ne atom. Although, to the authors’s knowledge, these are the largest close-coupling electron–polyatomic-molecule scattering calculations to date, the results lead to questions concerning the convergence of the close-coupling approach in the case of Rydberg-state excitation. Conclusions are drawn in the context of earlier results for electron-impact excitation of the H, He, and Ne atoms.

Cross sections for the ionization of ${\mathrm{Ar}}^{7+}$ by electron impact have been calculated using the R-matrix method in two independent 19- and 45-state close-coupling approximations. Autoionization states arising from the 2${\mathit{s}}^2$2${\mathit{p}}^5$3s3l configurations together with the ground and excited 2${\mathit{s}}^2$2${\mathit{p}}^6$3l states are included in the close-coupling expansion in the 19-state calculation, while additional autoionization states arising from the 2${\mathit{s}}^2$2${\mathit{p}}^5$3s4l (l=0,1,2) and 2s2${\mathit{p}}^6$3s3l configurations and the low-lying bound states 2${\mathit{s}}^2$2${\mathit{p}}^6$4l are also included in the 45-state calculation. Several Rydberg series of resonances converging to various autoionizing states are formed due to the resonant-excitation-double-autoionization process and these are found to significantly enhance the cross sections in the autoionizing threshold region. The calculated results are compared with the recent crossed-beam measurements.

We have investigated the relative excitation functions for low-lying singly excited and low-lying core-excited levels in S v (${\mathrm{S}}^{4+}$) to S ix (${\mathrm{S}}^{8+}$) after beam-foil excitation using ions in the energy range 2–10 MeV. The spectral line intensities have been normalized to the same number of particles at each ion energy and corrections for the level lifetimes have been made. The overall accuracy of the measured relative excitation function at each energy and charge state is estimated to be better than 2%. A comparison of the relative excitation functions for singly excited and core-excited lines shows a difference in S vii, but not in S vi.

Photoionization cross sections, branching ratios, and photoelectron angular-distribution asymmetry parameters have been calculated for the Yb (Z=70) 4f, 4d, and 6s subshells using the relativistic random-phase approximation, the truncated relativistic random-phase approximation, and the relativistic random-phase approximation, modified to include relaxation effects. Comparisons are made between the various approximations and experimental data. Important relaxation effects for the 4f and 4d channels are noted and strong effects of interchannel coupling are noted for 6s photoionization in the region near the 4f and 5p thresholds.

A calculation of e-${\mathrm{N}}_2$ scattering in the vicinity of the 2.4-eV (${\mathrm{\Pi }}_{\mathit{g}}$) resonance has been completed. The main element of the calculation is a 15-term vibrational close-coupling expansion, reduced to coupled two-dimensional partial differential equations (PDE’s), and solved using the noniterative PDE technique. The potential consists of static, exchange, and polarization parts; each part has been (previously) derived in a manner appropriate to its importance in the scattering equation. Results for the absolute total cross section, both in magnitude and shape of the substructure in the resonance region (1.5<${\mathit{k}}^2$<3 eV), are in excellent accord with experiment. Angular distributions are also calculated and found to vary significantly in shape for different energies in the immediate vicinity of the center of the resonance (2.05<${\mathit{k}}^2$<2.15 eV), indicating the need for differential measurements at a finer grid in energy and therefore requiring even better energy resolution. A comparison with other calculations and a discussion of some theoretical aspects are also included.

A molecular theory of collision-induced fine-structure-level transitions in complex atoms is presented. The theory is applied to calculate the excitation cross sections for the fine-structure levels in the ${}_{}{}^3{}_{}{}^{}$P ground state of atomic oxygen. We discuss and compare the theory presented here with previous molecular theories.

The interaction potential between metastable argon (${\mathrm{Ar}}^{\mathrm{*}}$) and xenon has been determined by a measurement of the velocity dependence of the total elastic-scattering cross section for the reaction ${\mathrm{Ar}}^{\mathrm{*}}$+Xe. The cross sections have been corrected for the inelastic contribution to the reaction. The potential parameters have been determined by comparing the data with potential parameters calculated with both semiclassical and full quantum calculations of the cross sections. The semiclassical computation resulted in a potential with a well depth of 18 meV and a position of 4.6 Å while the full quantum yielded a well depth of 25.4 meV and a position of 4.3 Å.

Density matrices are experimentally determined which describe H(n=2) atoms produced in electron-transfer collisions between 20–100-keV protons and helium. The density matrix contains the electron-transfer cross sections ${\mathrm{\sigma }}_{2\mathit{s}}$, ${\mathrm{\sigma }}_{2\mathit{p}0}$, and ${\mathrm{\sigma }}_{2\mathit{p}\pm 1}$, as well as the real and imaginary parts of the ${\mathit{s}}_0$${\mathit{p}}_0$ coherence. Experimentally, a monoenergetic proton beam traverses a helium gas cell producing hydrogen atoms H(n) via electron transfer. Within the gas cell an electric field is applied either axial or transverse to the proton beam. The Stokes parameters describing the intensity and linear polarization of Lyman-α radiation (122 nm) emitted by H(n=2) atoms are determined as a function of applied electric-field strength. The density-matrix elements are determined from a linear least-squares fit of the Stokes parameters to the set of five fitting functions which represent the contributions from individual density-matrix elements. The density-matrix results are self-consistent. Separate determinations using axial or transverse electric fields agree with each other. The general results indicate ${\mathrm{\sigma }}_{2\mathit{s}}$>${\mathrm{\sigma }}_{2\mathit{p}0}$>${\mathrm{\sigma }}_{2\mathit{p}\pm 1}$ between 20 and 100 keV. The electric dipole moment 〈d${\mathrm{〉}}_{\mathit{z}}$ has a value near zero at 20 keV rising to a maximum of about 1.3 a.u. near 40 keV and remaining nearly constant through 100 keV. The 〈L×A${\mathrm{〉}}_{\mathit{z},}$s moment has a maximum of about 0.5 a.u. at 25 keV, passing through zero near 70 keV. These results compare favorably with available experimental results and are qualitatively predicted by present theoretical models. Comparison with previous H(n=3) results indicates that the Runge-Lenz vector 〈A${\mathrm{〉}}_{\mathit{z}}$ is larger for n=3 than for n=2 and that 〈L×A${\mathrm{〉}}_{\mathit{z},}$s has the same values for both n.

Single-beam attenuation measurements of the velocity-dependent integral scattering cross sections for Ar${(}^3$${\mathit{P}}_{2,0}$)+${\mathrm{H}}_2$O are reported. The data are corrected for the finite angular resolution of the apparatus and the thermal motion of the target molecules. The measured total cross sections, which range from 505 A${\mathrm{̊}}^2$ at 0.708 km/s to 236 A${\mathrm{̊}}^2$ at 4.58 km/s, are analyzed semiclassically to obtain spherically averaged potential parameters and an upper limit to the inelastic cross section.

The spectral distribution of loosely bound target electrons emitted in collisions with fast bare projectiles is described in terms of electron capture to the projectile continuum. Comparison with experimental data on electron ejection from He by 1–5-MeV/amu ${\mathrm{H}}^{+}$, ${\mathrm{C}}^{6+}$, ${\mathrm{O}}^{8+}$, and ${\mathrm{F}}^{9+}$ impact into forward directions shows that the impulse approximation for rearrangement is able to describe the shape of the energy distribution not only at the cusp, but also in the binary-encounter region and beyond. The results of the post form of the impulse approximation are discussed in relation to the first-order Born approximation, the continuum distorted-wave theory, the fully peaked prior impulse approximation, and in particular the recently presented distorted-wave strong-potential Born approximation.

We report the results of close-coupling complex Kohn calculations of cross sections for electron-impact excitation of the water molecule into electronically dissociative states in the energy range from 8 to 30 eV. We have coupled five channels including the ${}_{}{}^1{}_{}{}^{}$${\mathit{A}}_1$ ground state and excited singlet and triplet states formed by promoting the occupied 3${\mathit{a}}_1$ and 1${\mathit{b}}_1$ electrons to the lowest unoccupied 4${\mathit{a}}_1$ orbital. These states have theoretical vertical energies in the range from 8 to 12 eV and are known to be dissociative. Our calculations have confirmed the existence of Feshbach resonances related to the ${\mathit{A}}_1$ and ${\mathit{B}}_1$ excited states which are responsible for dissociative attachment in water at rather high energies. We found that these resonances indeed correspond to configurations 3${\mathit{a}}_1$4${\mathit{a}}_1^2$ and 1${\mathit{b}}_1$4${\mathit{a}}_1^2$. Our results include both total and differential cross sections. We also make comparison between theory and available experimental data.

The resonating-group method developed for nuclear collisions is used to obtain equations describing the collisions of slow atoms. On one hand, these equations correctly take into account the indistinguish- ability of electrons and scattering boundary conditions and therefore are free from the drawbacks of conventional equations in the adiabatic electronic basis. On the other hand, they retain the form of the latter equations and therefore are in agreement with the generally accepted picture of heavy-particle motion in the fields of adiabatic electronic potentials accompanied by nonadiabatic transitions. The general theory is illustrated by considering the interaction of two ground-state hydrogen atoms in the Heitler-London electronic basis.

We present results of electron-sodium scattering for the 3D→3P transition at the projectile energy of 5 eV calculated using the convergent close-coupling method. These include spin-resolved and spin-averaged alignment, orientation, and coherence parameters, as well as differential cross section and spin asymmetry. This calculation simultaneously produces results for the transitions 3P→3P at 6.52 eV and 3S→3P at 8.62 eV, which are also presented. The three transitions are used to study the nature of the convergence in the close-coupling expansion. We find our results to be in excellent agreement with experiment, where available.

Atomic Al develops a population inversion and stimulated emission in the resonance lines when a solid target in a ${\mathrm{H}}_2$ buffer gas is irradiated with ArF 1930-Å laser light. We present experimental evidence that the ${\mathrm{H}}^{\mathrm{-}}$ ion is responsible for this effect, through charge-neutralizing collisions with ${\mathrm{Al}}^{+}$.

Based on first-order perturbation theory and the frozen-charge-state model, an analytical formula for the electronic stopping power was derived for swift lithiumlike and berylliumlike ions. The bound electrons attached to ions in the ground state were described by the Hartree-Fock-Slater determinant, in which the orbital-screening parameter in the constituent eigenfunctions was determined by the variational method. The stopping power -dE/dx for fast hydrogenlike to berylliumlike ions is found to be scaled in terms of (-dE/dx)${\mathit{Z}}_1^{\mathrm{-}\mathrm{\alpha }}$ where α ranges from 2.180 (H-like) to 2.355 (Be-like). The theoretical stopping for Li-like ions agrees quite well with the recent data on ∼10 MeV/amu ${\mathrm{O}}^{5+}$ ions.

The standard theory of multiple scattering of ions traversing matter assumes that the energy loss of a particle, during transit through a medium, is very small compared with its initial energy. Here we consider the effect of finite-energy losses on the multiple-scattering angular distributions, by taking into account the variation of the energy-dependent scattering cross section as a function of the depth penetrated into the material. The theory is generalized to account for a continuous slowing down of the beam particles. We study in particular, for the case of slow ions, the increased spread of the angular distributions due to the energy-loss effect.

Absolute integral cross sections for elastic collisions of neutral sodium clusters ${\mathrm{Na}}_{\mathit{n}}$ (n=2–20) with sodium atoms have been measured and the van der Waals interaction constants determined. The center-of-mass cross sections are very large (up to thousands of square angstroms), reflecting high cluster polarizabilities. It is found that the dispersion theory based on measured response parameters of alkali-metal clusters tends to overestimate the interaction strength.

We describe the results of three sets of experiments to investigate producing cold slow collimated potassium atoms for applications with no access available for the introduction of counterpropagating laser light along the exiting atomic beam’s axis. Velocity profiles are obtained via fluorescence from D1 excitation at perpendicular and nearly parallel incidence by a probe laser. Spatial profiles of both the cold- and residual hot-beam components are measured with a position-scanned hot-wire detector. Velocity-component holes and decelerated cold components are observed, along with direct evidence of perpendicular heating of the cold components. A first set of experiments uses a variant of conventional chirp cooling and/or hole burning. Light is introduced by a heated inclined mirror, while atoms exit through a slit in the mirror. Loss of intensity at low velocity is observed and discussed. A second set of experiments investigates velocity-selective optical-pumping crossover resonances that occur near the mirror, where the incident and reflected beams overlap for several alternative geometries. A third set of experiments investigates cold-beam production using laser-induced velocity selection and deflection. It provides a higher cold-atom intensity, along with the means to perform high-resolution spectroscopy.

We calculate the excitation rates of the 5 ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}_{3/2}$ and 5 ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}_{5/2}$ states of rubidium through the simultaneous absorption of two photons of different frequencies by the ground 5 ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$ state. We include spin-orbit effects in the contribution of the 5P and 6P states, situated between the initial and final states, which give rise to the resonance structure in the two-photon spectrum. We indicate how our results can be used for the case in which the transition takes place between states with specified total angular momenta F, for both ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$. For the case of counterpropagating photons with the same frequency, our results are compared with existing experimental data.