Measurements are reported of mean energies of argon recoil ions produced by beams of 23-MeV ${\mathrm{Cl}}^{5+,8+,10+}$ or 19-MeV ${\mathrm{F}}^{9+}$, and of neon recoil ions produced by beams of 22-MeV ${\mathrm{Cl}}^{4+}$, detected in coincidence with the charge-changed outgoing projectile. A screened-elastic-Coulomb-scattering calculation permits estimation of impact parameters characteristic of each pair (q,r) of final projectile- (q) and recoil- (r) ion charge states. The results are found to be in good agreement with impact parameters deduced from measured cross sections and do not require measurement of projectile scattering angle.

We have investigated the radiative interference effects in the electron-recombination process on the groups of mutually overlapping double-excited states of a heliumlike multicharged ion. Numerical calculations for the cross section of dielectronic recombination with ${\mathrm{U}}^{91+}$ are presented. The relative magnitude of the effects is found to reach about 25%.

The relative cross section for photoionization from the 4s5p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ excited level of neutral calcium has been measured using pulsed laser excitation and ionization of Ca atoms in an atomic beam. Photoelectrons are counted as a function of ionizing photon energy and polarization. Measurements cover the energy range from 51 300 to 51 700 ${\mathrm{cm}}^{\mathrm{-}1}$ above the Ca ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ ground state at a resolution of approximately 0.15 ${\mathrm{cm}}^{\mathrm{-}1}$. The shapes and relative peak heights of resonances corresponding to the previously identified ${}_{}{}^3{}_{}{}^{}$${\mathit{S}}_1$ and ${}_{}{}^3{}_{}{}^{}$${\mathit{D}}_{1,2}$ autoionizing levels from the 3d4d configuration have been determined. A new, extremely strong resonance is also evident at 51 467 ${\mathrm{cm}}^{\mathrm{-}1}$, and it has been tentatively identified with the 3d4d ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ level. This is an experimental identification of a doubly excited even-parity singlet level in calcium.

We measured cross sections of target He atoms (${\mathrm{\sigma }}_{\mathit{T}}$) and those of electron capture into the excited levels of projectile ions (${\mathrm{\sigma }}_{\mathit{P}}$) for He 3 ${}_{}{}^{1,3}{}_{}{}^{}$S,P,D levels in ${\mathrm{He}}^{+}$-He symmetric collisions in the energy range 20–300 keV. By phenomenological analysis of the excitation functions, we found structures characteristic of the intermediate-velocity regime for both ${\mathrm{\sigma }}_{\mathit{T}}$ and ${\mathrm{\sigma }}_{\mathit{P}}$: the magnitudes and the velocities of the peak positions of the structures show notable dependence on the angular-momentum states of the levels. Similar dependence on angular-momentum states is also recognized in the excitation functions for electron capture by protons into H(3,l) levels in ${\mathrm{H}}^{+}$-Li and ${\mathrm{H}}^{+}$-He collisions obtained by other investigators. This fact suggests close correlation between the behaviors of the excitation functions and the angular-momentum states of the initial and the final states, because all the processes mentioned above are concerned with electron transfer from the s level to upper s, p, and d levels. A simple momentum-matching electron-transfer model explains the observed characteristics qualitatively. Characteristics observed for the structures of ${\mathrm{\sigma }}_{\mathit{P}}$ are also observed for the structures of ${\mathrm{\sigma }}_{\mathit{T}}$, although the structure of ${\mathrm{\sigma }}_{\mathit{P}}$ appears in a velocity range about 1.4 times larger than that for the structure of ${\mathrm{\sigma }}_{\mathit{T}}$. Thus we expect that the same kind of mechanism that governs electron capture into excited states also causes target excitation accompanied by electron exchange.

Total electron-detachment cross sections ${\mathrm{\sigma }}_{\mathit{e}}$ for collisions of ${\mathrm{F}}^{\mathrm{-}}$, ${\mathrm{Cl}}^{\mathrm{-}}$, ${\mathrm{Br}}^{\mathrm{-}}$, and ${\mathrm{I}}^{\mathrm{-}}$ with atomic hydrogen have been measured for relative collision energies E ranging from 0.1 to 20 eV. For ${\mathrm{F}}^{\mathrm{-}}$, ${\mathrm{Cl}}^{\mathrm{-}}$, and ${\mathrm{Br}}^{\mathrm{-}}$, ${\mathrm{\sigma }}_{\mathit{e}}$ is found to decrease with increasing E and is fairly well described by a simple orbiting model in which an effective polarizability is used to describe the interaction of the anion with atomic hydrogen at small internuclear separations. For the system ${\mathrm{I}}^{\mathrm{-}}$+H, ${\mathrm{\sigma }}_{\mathit{e}}$ increases with increasing collision energy. The measured ${\mathrm{\sigma }}_{\mathit{e}}$ for ${\mathrm{Cl}}^{\mathrm{-}}$+H is also found to agree well with calculations based on an effective-range approximation. Charge-transfer cross sections have been measured for ${\mathrm{F}}^{\mathrm{-}}$, ${\mathrm{Cl}}^{\mathrm{-}}$, and ${\mathrm{I}}^{\mathrm{-}}$+H and are found to be small.

An exact analytical solution in terms of the Meijer functions is obtained from the quantum Rosen-Zener-Demkov model for nonadiabatic transitions. The N matrix for the nonadiabatic transitions, the S matrices, and the probabilities for elastic and inelastic atomic collision channels are found.

Ab initio potential-energy curves and radial and rotational coupling matrix elements have been calculated by means of configuration-interaction methods. A semiclassical treatment including electron translation factors has been performed in the (0.1–1.5)×${10}^8$ cm/s velocity range and provides a good agreement with experiment.

The inner-valence-photoelectron spectrum of argon has been recorded between 28 and 40.8 eV at a resolution of 20 meV using monochromatized He ii alpha excitation. More than 40 lines are observed and assigned by comparison to optical data and theoretical results. Except for the 3s single-hole state at 29.240 eV, the spectrum is associated with transitions to electron-correlation states arising from 3${\mathit{p}}^4$ nl configurations, where n=3,4,5 and l=0–3. The complete manifold of ionic states is observed for most configurations. Final states with an angular momentum up to J=9/2 acquire a substantial intensity.

We have studied the angular distributions for 6–30-MeV ${\mathrm{C}}^{\mathit{q}+}$ (q=4–6) and 2–9-MeV ${\mathrm{H}}^{+}$ ions axially channeled in the [001] direction of a thin silicon crystal (1792 and 1900 Å). We report highly structured two-dimensional angular distributions that depend sensitively on the projectile’s velocity and incident charge state and the target’s thickness and azimuthal orientation. Some structure in the angular contour maps is the result of a rainbow effect in axial channeling (i.e., extrema in the classical deflection function). State-to-state charge-state distributions, which are required to interpret the data accurately, have also been measured. All measured angular distributions have been explained via Monte Carlo trajectory calculations using Moliere’s approximation to the Thomas-Fermi screening function and a screening length given by target electrons alone. The calculations indicate that all projectile velocity and charge-state effects and the target-thickness effects observed are the result of the projectile’s transverse oscillatory motion in the channel. Using this information, we show that swift heavy-ion and proton angular distributions are simply related using a scaling law that depends only on the projectile’s velocity and charge-to-mass ratio and on the crystal thickness.

Total and partial photoionization cross sections, branching ratios, and angular-distribution asymmetry parameters for inner subshells (nl,l≥2) of the group-IIB elements zinc, cadmium, and mercury have been calculated in both the relativistic random-phase approximation and the relativistic random-phase approximation modified to include relaxation. Comparisons are made between the results of the two theoretical methods and with experiment where available. The present theoretical results for the 3d inner-shell photoionization of zinc are not in accord with experiment. We confirm previous work [S. L. Carter and H. P. Kelly, J. Phys. B 11, 2467 (1978)] which demonstrated that relaxation is an important effect in photoionization of the 4d subshell of atomic cadmium. It is also found that the inclusion of relaxation effects resolves a discrepancy between theory and experiment for the 4f inner-shell photoionization of atomic mercury.

The influence of a distorted nuclear motion on electron capture from the inner shells of atoms, when atomic model potentials, rather than scaled Coulomb potentials, are used in the motion of the active target electron, is investigated in the distorted strong-potential Born approximation to the exact capture amplitude. A comparison is made with the earlier undistorted strong-potential Born approximation and other theories, and with experiment. The modification of the impulse-approximation cross section is shown to be generally much less in the distorted theory and is shown to give quite good agreement with the experimental data. At energies below the peak in the capture cross sections, the present results show significantly better agreement with experiment and also good agreement with the recent coupled-Sturmian-pseudostate results of Winter [Phys. Rev. A 47, 264 (1993)], who used the same atomic model potential.

WKB calculations have revealed that tunneling dynamics of localized wave packets in simple potential wells depend sensitively on the degree of squeezing of the wave function. Squeezed states are shown to tunnel more slowly in general than eigenstates of the well and states which are initially localized near the bottom of a well have much lower tunneling rates than states localized at the sides of the well. The dependence of tunneling time on energy also exhibits steps related to quasi-bound-state energies in a complex way. Additionally, modulations in the tunneling probability correlate with the motion of the squeezed wave packet in the well. These results have implications both for the dynamics of squeezed radiation fields and squeezed matter states, and examples of applications to controlled vibrational-state chemistry, ultralow-noise measurements of weak signals with Josephson junctions, and optical crystals are discussed.

The charge-state and energy distribution of molecular ions and fragments produced in low-energy, highly-charged-argon-ion collisions with ${\mathrm{N}}_2$ and CO were measured. ${\mathrm{Ar}}^{\mathit{q}+}$ (8≤q≤14) ions produced by an electron-beam ion source and extracted at 2.3 kV interacted with a molecular-target gas jet located in the ionization region of a time-of-flight spectrometer. The resulting molecular recoils and fragments were analyzed by time of flight. For a given molecular target, the measured spectra are all similar and do not depend on the incident argon-projectile charge state. The spectra are dominated by the singly charged ion, either ${\mathrm{N}}_2^{+}$ or ${\mathrm{CO}}^{+}$. The stable or long-lived metastable doubly charged molecular ion ${\mathrm{CO}}^{2+}$ is the second most prominent feature in ${\mathrm{Ar}}^{\mathit{q}+}$ on the CO spectra. Similarly, ${\mathrm{N}}_2^{2+}$, which cannot be distinguished from ${\mathrm{N}}^{+}$, is also presumed to be present in ${\mathrm{Ar}}^{\mathit{q}+}$ on the ${\mathrm{N}}_2$ spectra. The remaining peaks are associated with the dissociation of the ${\mathrm{N}}_2^{\mathit{Q}+}$ and ${\mathrm{CO}}^{\mathit{Q}+}$ (2≤Q≤6) molecular ions formed in the collision. The peak positions correspond to fragments of a given mass-to-charge ratio and kinetic energy calculated assuming vertical target ionization.

Ionization cross sections for the L subshells of Pb and Bi by α-particle bombardment (2.2–8.2 MeV) have been determined from the experimental data and the currently available radiative transition probabilities, fluorescence yields, and Coster-Kronig factors. The measured ionization cross sections and their ratios are compared with the results of ECPSSR calculations [ECPSSR denotes perturbed-stationary-state (PSS) theory with energy-loss (E), Coulomb deflection (C), and relativistic (R) corrections]. The measured individual cross sections for ${\mathit{L}}_1$ and ${\mathit{L}}_2$ subshells deviated in opposite directions from the theory, whereas their sum shows good agreement. The ${\mathit{L}}_3$ and total ionization cross sections obtained from the data also show good agreement with the ECPSSR theory. The ionization cross-section ratios ${\mathrm{\sigma }}_{\mathit{L}1}$/${\mathrm{\sigma }}_{\mathit{L}2}$ and ${\mathrm{\sigma }}_{\mathit{L}3}$/${\mathrm{\sigma }}_{\mathit{L}2}$ show large deviations from the ECPSSR theory. The experimental x-ray production cross-section ratios are found to be in better agreement with the theoretical results obtained from using ECPSSR ionization cross sections and the decay yield data of Xu and Xu [J. Phys. B 25, 695 (1992)] rather than those obtained from using the decay yield data of Krause [J. Phys. Chem. Ref. Data 8, 307 (1979)]. The x-ray production cross sections, however, are in better agreement with the theoretical results obtained from using the decay yield data of Krause. The measured centroid energy of the Lγ lines of Pb shows large deviations at high projectile energy, whereas for Bi large deviations are found at the low-energy region.

Analytical expressions for cross sections for ionization of muonic hydrogenlike atoms by nonrelativistic electrons are derived using the classical impulse approximation.

A theoretical relation between the electron scattering length and the van der Waals approximation to the equation of state is described. The theory provides a simple calculation for the scattering length of neutral atomic scatterers such as rare gases, using two experimental parameters: the hard-core radius (calculated from the van der Waals equation of state, using critical data) and the atomic polarizability. The results for the calculated electron scattering length agree with measured values derived either from the energy shifts of highly excited molecular Rydberg states, perturbed by He, Ne, Ar, Kr, and Xe, or from swarm electron cross-section data for the same gases.

Absolute doubly differential cross sections for electron emission are presented for 0.5-MeV/u multicharged ion-atom collisions. The collision systems investigated are ${\mathrm{B}}^{\mathit{q}+}$, ${\mathrm{C}}^{\mathit{q}+}$ (q=2–5) and ${\mathrm{O}}^{\mathit{q}+}$, ${\mathrm{F}}^{\mathit{q}+}$ (q=3–6) projectiles impacting on helium and ${\mathrm{C}}^{\mathit{q}+}$ (q=2–5) ions impacting on neon and argon targets. Laboratory electron emission angles between 10° and 60° were studied. Under the assumption that the cross sections scale with the square of an effective projectile charge, ${\mathit{Z}}_{\mathit{e}\mathit{f}\mathit{f}}$(ɛ,θ), the scaling was investigated as a function of emitted electron velocity and angle. For distant collisions (low-energy electron emission), we find that ${\mathit{Z}}_{\mathit{e}\mathit{f}\mathit{f}}$(ɛ,θ)>q for small q. For the highest values of q investigated, ${\mathit{Z}}_{\mathit{e}\mathit{f}\mathit{f}}$(ɛ,θ) was found to be smaller than the net projectile charge q. The effective projectile charges may be subject to a systematic underestimation since they were determined by referencing the partially stripped ion impact data to fully stripped boron, rather than proton, impact cross sections. In the binary-encounter region, the present data confirm previously observed features–namely that the emission increases as q decreases. For the helium target, the qualitative behavior is roughly in accordance with predictions by Schulz and Olson [J. Phys. B 24, 3409 (1991)]. Neon and argon targets also demonstrate these features, but less dramatically than helium.

An experiment to measure the dielectronic recombination of ${\mathrm{C}}^{3+}$ in a known external electric field is described. The measured value differs from results of calculations which do not include the effects of field enhancement, and is larger than but marginally in agreement with predictions of theoretical methods that include the effects of the external field.

We report absolute, state-selective cross sections for single-electron capture by He-like ions (${\mathrm{N}}^{5+}$, ${\mathrm{O}}^{6+}$, ${\mathrm{F}}^{7+}$, ${\mathrm{Ne}}^{8+}$) colliding on He which were determined by vuv photon-emission spectroscopy. The impact energy was varied between 0.05 and 2 keV ${\mathrm{amu}}^{\mathrm{-}1}$. The experimental data are compared with theoretical predictions based on the classical overbarrier model, the Landau-Zener model, and existing close-coupling calculations.

The cross sections for radiative electron capture (REC) into the K shell of bare and H-like light ions of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, and ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ are measured at different energies, under channeling conditions using a Si single crystal as target. These cross section data using different projectiles are shown to fall on a universal curve when plotted against a scaled variable, the adiabaticity parameter ${\mathrm{\eta }}_{\mathit{K}}$, of the collision systems. We have observed a definite difference in the cross section between the present solid target data and the available data for a gas target at the same ${\mathrm{\eta }}_{\mathit{K}}$ value. This difference, along with the observed shift in the REC photopeak energy, suggests an ‘‘ion-solid-state’’ effect. Further, these observations, especially their Z dependence, are consistent with the predictions of the theory.