We present a general analysis of the close-coupling equations for e-He scattering. We show why the standard close-coupling expansion gives rise to nonunique solutions and, by characterizing the manifold of nonunique solutions, are able to construct equations with a unique solution. Our analysis concentrates on two models of target states; a frozen-core model in which one of the electrons is restricted to the 1s ${\mathrm{He}}^{+}$ orbital, as has been used with great success recently, and also a model which uses full configuration-interaction target states. We develop modified close-coupling equations by projecting out spurious solutions. A subtle difference between frozen-core and configuration-interaction models with respect to the manner in which antisymmetrization is incorporated is noted. A calculation to illustrate the theory is presented.

Dielectronic recombination (DR) in the average-atom (AA) model has been studied. The reasonableness of directly applying the Burgess-Merts (BM) formula to the AA model has been examined. We have noticed that it is inappropriate to use the BM formula to calculate DR rate coefficients for average ions. We have developed a self-consistent-field theoretical method to treat the DR for average ions with electrons. As an example, the DR rate coefficients for argon have been calculated at a defined electron population, and have been compared with the rate-coefficient average via detailed configuration accounting.

The coupling between angular momenta during low-energy collisions of slow positrons as projectiles on simple diatomics like ${\mathrm{H}}_2$ and ${\mathrm{N}}_2$ is analyzed from the point of view of its effect on vibrationally inelastic processes and on possible decoupling schemes that can help to simplify calculations. It is found that the strong decoupling between rotational and vibrational degrees of freedom implied by the well-known infinite-order-sudden approximation (here used within the vibrational close-coupling-rotational-infinite-order-sudden scheme discussed below) is not valid for positron scattering at low collision energies in spite of its low excitation efficiency for the vibrational degrees of freedom of the target molecules.

We have measured the energy levels and purely rotational autoionization rates of 25 different triplet Rydberg states of the ${\mathrm{H}}_2$ molecule with quantum numbers n=14–29, L=3, v=0, and R=2–4. Electron impact excites the ground-state molecules in a beam to the metastable c(2p)${\mathrm{}}^3$ ${\mathrm{\Pi }}_{\mathrm{u}}$ states. Two-color laser excitation from two counterpropagating single-mode cw dye laser beams excites the metastable molecules through an intermediate (3d)${\mathrm{}}^3$ Σ or (3d)${\mathrm{}}^3$ Π state to the triplet nf Rydberg states. The linewidths of the transitions to the Rydberg states give the autoionization rates, which vary widely and agree satisfactorily with the quadrupole-moment-polarizability long-range Coulomb interaction model. The laser transitions have been measured to 0.002 ${\mathrm{cm}}^{\mathrm{-}1}$ . We use these measurements, the model, and an extrapolation of the Rydberg series to derive the ionization potential of the metastable c(2p)${\mathrm{}}^3$ ${\mathrm{\Pi }}_{\mathrm{u}}$ v=0 states with an accuracy of 0.020 ${\mathrm{cm}}^{\mathrm{-}1}$ and the energy difference between the singlet ground state and the triplet metastable c(2p)${\mathrm{}}^3$ ${\mathrm{\Pi }}_{\mathrm{u}}$ states with an accuracy of 0.025 ${\mathrm{cm}}^{\mathrm{-}1}$ . This allows the whole singlet and triplet manifolds of ${\mathrm{H}}_2$ to be linked together with higher accuracy: our correction to Dieke's ${\mathrm{H}}_2$ triplet term values is -149.704(25) ${\mathrm{cm}}^{\mathrm{-}1}$ .

We present state-dependent and total charge transfer cross sections for the process ${\mathrm{Si}}^{4+}$(${2\mathrm{p}}^6$)+He(${1\mathrm{s}}^2$)→${\mathrm{Si}}^{3+}$(3l)+${\mathrm{He}}^{+}$(1s), where l=s,p, in the collision energy range 0.004–10 eV/amu. The cross sections are determined using a close-coupled quantal method. Fully ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond method are incorporated. Rate coefficients for temperatures between 1000 and 50 000 K and results for isotopic ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ are also presented. Astrophysical applications are briefly discussed.

The optical excitation function of prompt Lyman-α radiation, produced by electron impact on atomic hydrogen, has been measured over the extended energy range from threshold to 1.8 keV. Measurements were obtained in a crossed-beams experiment using both magnetically confined and electrostatically focused electrons in collision with atomic hydrogen produced by an intense discharge source. A vacuum-ultraviolet monochromator system was used to measure the emitted Lyman-α radiation. The absolute H(1s-2p) electron impact excitation cross section was obtained from the experimental optical excitation function by normalizing to the accepted optical oscillator strength, with corrections for polarization and cascade. Our data are significantly different from the earlier experimental results of R. L. Long et al., J. Res. Natl. Bur. Stand. Sect. A 72A, 521 (1968) and J. F. Williams, J. Phys. B 9, 1519 (1976); 14, 1197 (1981), which are limited to energies below 200 eV. Statistical and known systematic uncertainties in our data range from ±4% near threshold to ±2% at 1.8 keV. Multistate coupling affecting the shape of the excitation function up to 1 keV impact energy is apparent in both the present experimental data and present theoretical results obtained with convergent close-coupling (CCC) theory. This shape function effect leads to an uncertainty in absolute cross sections at the 10% level in the analysis of the experimental data. The derived optimized absolute cross sections are within 7% of the CCC calculations over the 14 eV–1.8 keV range. The present CCC calculations converge on the Bethe-Fano profile for H(1s-2p) excitation at high energy. For this reason agreement with the CCC values to within 3% is achieved in a nonoptimal normalization of the experimental data to the Bethe-Fano profile. The fundamental H(1s-2p) electron impact cross section is thereby determined to an unprecedented accuracy over the 14 eV – 1.8 keV energy range.

The influence of the projectile velocity on the ${\mathrm{m}}_{\mathrm{\ell }}$ distributions of the ${\mathrm{Ar}}^{7+}$ excited states produced by electron capture during ${\mathrm{Ar}}^{8+}$-Li(2s) collisions is studied experimentally between 1.5 and 4.5 keV ${\mathrm{amu}}^{\mathrm{-}1}$ by measuring the polarization of the emitted light, and theoretically between 1 and 4 keV ${\mathrm{amu}}^{\mathrm{-}1}$ by using the classical trajectory Monte Carlo (CTMC) method. We investigate the 7${\mathrm{\ell }}^{|\mathrm{I}\mathrm{H}}$-8ℓ and 8${\mathrm{\ell }}^{|\mathrm{I}\mathrm{H}}$-9ℓ radiative transitions subsequent to the decay of the 8ℓ and 9ℓ sublevels of Ar VIII, which are preferentially populated by the single electron capture process. A small but not negligible effect is seen for the experimental polarization ratios relating to transitions from sublevels of large ℓ values, showing a slight increase of the component parallel to the incident ion beam as the projectile energy increases. Theoretical polarization ratios obtained from CTMC calculated ${\mathrm{m}}_{\mathrm{\ell }}$ distributions are in excellent agreement with the measured polarization ratios. Electronic energy curve calculations are then presented in order to discuss these results in terms of dynamical couplings.

We present calculations of electron detachment from slow ${\mathrm{H}}^{\mathrm{-}}$ ions with excited He and Li atoms. The theoretical method is based on a close-coupling expansion of the electronic wave function and makes use of a discretization technique to describe the continuum. The calculated cross sections for these processes typically vary from ≃${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^2$ at 50 meV to ${10}^{\mathrm{-}14}$ ${\mathrm{cm}}^2$ at 20 eV and are the result of (i) the attractive nature of the interatomic potential and (ii) the Stark mixing induced by the ion on the excited neutral atom.

The elastic scattering of electrons from krypton atoms is calculated in a relativistic multiconfiguration method. The correlation effects responsible for target polarization are treated in a relativistic configuration-interaction scheme that allows for dynamic effects. Calculations of the spin polarization S at 5, 10, 15, and 20 eV are discussed and compared with experimental and other theoretical data. We also show spin-polarization trajectories that represent all three scattering parameters S, T, and U in a single computationally significant curve.

The ion charge state yields resulting from the photoionization of neon gas have been measured with time-of-flight ion charge state spectroscopy for excitation energies in the K-edge region. The decay of the [1s]3p resonance excited state results in the formation ion charge states ${\mathrm{Ne}}^{+}$,${\mathrm{nNe}}^{2+}$,${\mathrm{nNe}}^{3+}$, and ${\mathrm{Ne}}^{4+}$, with a branching ratio of 0.65:0.32:0.030:0.002, whereas the final charge state for the decay of higher-order [1s]np(n⩾4) and [1s]ɛp continuum excitations is mostly ${\mathrm{Ne}}^{2+}$. We have measured q-bar, the mean charge from photoionization, for excited states near the K edge as a function of photon energy. Postcollision interaction effects are shown to be quite small.

Knowledge of the incident ion's atomic number (${\mathrm{Z}}_1$) dependence of ion-induced electron emission yields can be the basis for a general understanding of ion-atom interaction phenomena and, in particular, for the design of ${\mathrm{Z}}_1$-sensitive detectors that could be useful, for example, in the separation of isobars in accelerator mass spectrometry. The ${\mathrm{Z}}_1$ dependence of ion-induced electron emission yields, γ, has been investigated using heavy ions ${\mathrm{C}}^{3+}$, ${\mathrm{O}}^{3+}$, ${\mathrm{F}}^{+3\mathrm{}}$, ${\mathrm{Na}}^{3+}$, ${\mathrm{Al}}^{3+}$, ${\mathrm{Si}}^{3+}$, ${\mathrm{P}}^{3+}$, ${\mathrm{S}}^{3+}$, ${\mathrm{Cl}}^{3+}$, ${\mathrm{K}}^{3+}$, ${\mathrm{Ti}}^{3+}$, ${\mathrm{Cr}}^{3+}$, ${\mathrm{Mn}}^{4+}$, ${\mathrm{Fe}}^{4+}$, ${\mathrm{Co}}^{4+}$, ${\mathrm{Ni}}^{4+}$, ${\mathrm{Cu}}^{4+}$, ${\mathrm{Ga}}^{4+}$, ${\mathrm{As}}^{5+}$, ${\mathrm{Br}}^{5+}$, ${\mathrm{Ru}}^{7+}$, ${\mathrm{Ag}}^{7+}$, ${\mathrm{Sn}}^{7+}$, and ${\mathrm{I}}^{8+}$ of identical velocity (v=${2\mathrm{v}}_0$, where ${\mathrm{v}}_0$ is the Bohr velocity) normally incident on 50 μg/${\mathrm{cm}}^2$ sputter-cleaned carbon foils. Measured yields as a function of ${\mathrm{Z}}_1$ reveal an oscillatory behavior with pronounced maxima and minima. Contrary to previously reported yields that assumed a monotonically increasing empirical mean charge state for the exiting ion, the present work indicates the ${\mathrm{Z}}_1$ oscillations in the experimentally measured yields, a fact masked in previous work. The strong ${\mathrm{Z}}_1$ oscillations can only be observed by simultaneous measurement of the yield and the mean charge state.

We have experimentally studied the backward electron emission from solid carbon bombarded by ${\mathrm{H}}^{+}$, ${\mathrm{H}}^0$, ${\mathrm{H}}^{\mathrm{-}}$, and ${\mathrm{H}}_2^{+}$ projectiles at MeV energies. We used a coincidence ion-by-ion technique that allows us to obtain not only the average electron yields but also the emission statistics. The comparison of energy dependences of electron emission due to ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^0$ projectiles helps to specify the role of the incident electron of ${\mathrm{H}}^0$. For ${\mathrm{H}}^{\mathrm{-}}$ and ${\mathrm{H}}_2^{+}$, the equality of electron yields above 500 keV/u supports the idea that backward emission is due to distant collisions.

The behavior of superslow neutrons with velocities lower than ≈0.1 m/s cannot be described by employing the notion of an average or optical potential. Owing to the existence of such a region, the wave vector in the medium becomes complex when a scattering length of an individual nucleus is positive. As a consequence, slow infiltration deep into the substance of ultracold neutrons with energies lower than the boundary energy takes place. Taking into account the weak absorption results in the appearance of a second branch in the neutron wave spectrum. It is characterized by a significantly longer damping length than predicted by the conventional theory of a complex potential. In the Conclusion possibilities of experimental verification of the theory are discussed.

The angle and temperature dependence of the photon scattering rate for Bose-stimulated atom recoil transitions between occupied states is compared to diffraction and incoherent Rayleigh scattering near the Bose-Einstein transition for an optically thin trap in the limit of large particle number N. Each of these three processes has a range of angles and temperatures for which it dominates over the others by a divergent factor as N→∞.

I specialize the Hartree-Fock, random-phase, and configuration-interaction approximations to a system of interacting bosons in an external potential. This approach affords a more direct connection to the methods and language of atomic-structure calculations. The derivations and equations parallel those found in atomic structure and are contrasted with the more commonly used Bogoliubov approach for bosons. I present a numerical method for solving the Hartree-Fock and random-phase equations to obtain the low-lying excitation energies for trapped alkali-metal atoms.

We present a theoretical analysis of the influence of surface roughness on the atomic reflection from an evanescent wave mirror. In our calculations we assume that light scattered at the rough dielectric surface interferes with the evanescent wave, creating a rough potential that scatters the atoms. We calculate the probability of diffuse reflection and the momentum distribution of the scattered atoms with a statistical model for the rough surface. The atomic reflection is diffuse rather than specular if the surface roughness is comparable to the wavelength of the incident atoms. We discuss the spatial coherence of the reflected matter waves. We indicate how to generalize our treatment to the case of multilevel atoms.

The coordinate-momentum double distribution function ρ(r-→,p-→)${\mathrm{d}}^3$${\mathrm{rd}}^3$p is calculated in the local density approximation for bosons with positive scattering length a in a trap. The calculation is valid to the first order of a. To clarify the meaning of the result, it is compared for a special case with the double distribution function ${\mathrm{\rho }}_{\mathrm{w}}$${\mathrm{d}}^3$${\mathrm{rd}}^3$p of Wigner.

The ionization dynamics of small rare-gas clusters in intense, ultrafast laser fields are studied via classical trajectory Monte Carlo simulations. Our results indicate that for similar laser pulses the charge states reached by atoms in a cluster can be significantly higher than those for atoms in the gas phase. The ionization enhancement is strongly dependent on the cluster density and exhibits a rapid increase in charge state once the laser intensity has reached the threshold for single ionization. This 'ionization ignition model' is driven by the combination of the laser field and the strong field from the ionized cluster atoms. Approximate atomic inner-shell ionization probabilities are calculated for several cluster densities and peak laser intensities and provide evidence for the generation of inner-shell holes on an ultrafast time scale. This is a necessary condition for the generation of x-ray pulses with temporal widths comparable to that of the driving laser pulses.

We have developed a full three-dimensional quantum scattering approach to optical suppression of ultracold-collision rates. These calculations are carried out assuming colliding atoms without fine or hyperfine structure, which have a ${}_{}{}^1{}_{}{}^{}\to _{}^1{}_{}{}^{}$P transition. The three-dimensional model predicts that the optical suppression of ultracold-collision rates saturates with light intensity much more slowly than predicted by two-level curve-crossing models. Circularly polarized light is significantly more effective for optical suppression, and causes less increase in atomic kinetic energy due to excited-state production than linearly polarized light. The suppressor optical field can also cause orders of magnitude increases in ground-state elastic-scattering rates.

We study the evolution of coherent and Schrödinger cat states in radio-frequency traps, which were used to bound ${\mathrm{Hg}}^{+}$ ions. The quantum confinement is determined by evaluating the expectation values and dispersions of the position and momentum operators, together with the probability densities in coordinate and momenta representations. Also the Wigner functions associated to this nonstationary quantum system, a parametric oscillator, are constructed.