The empirically observed isoelectronic linearization of alkali-metal-like line strengths ${\mathit{Z}}^2$S=A+B/(Z-C) is examined for the Li, Na, Cu, and Ag sequences. It is found that small deviations from this linearity observed at high Z can be removed by use of a correction factor obtained from the relativistic formulation of the hydrogenlike line strength. With this correction, low-Z data can be linearly interpolated to the nonrelativistic hydrogenic value in the high-Z limit. The linearization is tested in the data-rich Li, Na, and Cu sequences and is utilized to make precise predictions for the Ag sequence on the basis of a small number of accurate measurements.

Following Bhatia and Temkin [Rev. Mod. Phys. 36, 1050 (1964)] we decompose the Hamiltonian of a two-electron atom (or ion) with a fixed nucleus in terms of Euler angles, and thereby reduce the energy-eigenvalue problem to a set of coupled equations involving only three lengths, the distance of the electrons from each other and the distances from the nucleus. However, our equations differ from those of Bhatia and Temkin since we use a different expansion of the wave function. When the total orbital-angular-momentum quantum number L is zero or one our equations are the same as those derived by Hylleraas [Z. Phys. 48, 469 (1928)] and Breit [Phys. Rev. 35, 569 (1930)]. We give the transformation relating the generalized Hylleraas-Breit equations to the equations of Bhatia and Temkin. Our derivation is facilitated by a special factorization of one-particle angular-momentum operators.

The Kirschbaum-Wilets quasiclassical, many-body atomic model [Phys. Rev. A 21, 834 (1980)] is applied to atoms and ions having 1≤Z≤38. An efficient method was found to search for the global minimum of the energy functional. A quasiclassical shell structure is shown to result from the Hamiltonian formulation in terms of momentum-dependent potentials representing quantum-mechanical effects codified in the Heisenberg and Pauli principles. Along with ionization and correlation energies, the ground-state configurations are presented for use as initial conditions in various dynamical calculations.

A series of multiconfiguration (MC) Dirac-Hartree-Fock (DHF) calculations were performed to study the effects of correlation on the energy difference between the [Rn]5${\mathit{f}}^{14}$7${\mathit{s}}^2$7${\mathit{p}}_{1/2}$, J=1/2, odd-parity (1/$2^{\mathit{o}}$) and the [Rn]5${\mathit{f}}^{14}$6${\mathit{d}}_{3/2}$7${\mathit{s}}^2$, J=3/2, even-parity (3/$2^{\mathit{e}}$) levels of atomic lawrencium. In particular, the effects of interactions between valence and core electrons were investigated. Single-configuration DHF calculations predict that the 1/$2^{\mathit{o}}$ level lies below the 3/$2^{\mathit{e}}$ level; the correlation effects included in the MCDHF calculation tend to reverse this ordering. For comparison, similar studies were also carried out for Y and LU, where observed related energy differences are available.

The K${\mathrm{\alpha }}_{1,2}$ and K${\mathrm{\beta }}_{1,3}$ spectra of copper were measured using double- and single-crystal diffractometers whose finite resolution effects were carefully characterized and corrected for. A phenomenological resolution of the spectra into Lorentzians is given, yielding excellent R factors close to 1%. Fits to our detailed relativistic Dirac-Fock and nonrelativistic Hartree-Fock ab initio calculations reveal that the line shapes can be accounted for by the diagram and the single 3d spectator hole transitions only, with R factors of 3–5 % (the underline below 3d denotes a hole state). The contribution of the 3d spectator transitions to each of the spectra is 26–30 %. The Kα spectrum may also contain a small ∼0.5% contribution from the 3p spectator transition. The fit residuals of the Kβ spectrum show systematic deviations in the vicinity of the β’ feature, which may be due to exchange interactions or plasmon excitations. Contributions of similar origins to the Kα spectrum were not detected. Linewidths, energies, and intensities are reported, for the raw as well as the fit-resolved spectra, and critically compared with previous data, where available.

Structure and QED effects for 2${\mathit{s}}_{1/2\mathrm{-}}$2${\mathit{p}}_{3/2}$ transitions in lithiumlike, berylliumlike, carbonlike, fluorinelike, and neonlike uranium are calculated and compared with recent measurements. With the exception of berylliumlike uranium, which has poor convergence properties, good agreement with experiment is found.

Detailed qualitative x-ray absorption spectra near the K edge of ${\mathrm{Br}}^{\mathrm{-}}$ in organic solvents have been measured using synchrotron radiation. Several structures similar to those assigned to multielectron excitations in noble gases were detected on ${\mathrm{Br}}^{\mathrm{-}}$ in solution. They were analyzed in terms of the shake-up and shake-off processes. The [1s4p], [1s4s], [1s3d], and [1s3p] transitions have been identified and two additional absorption edges have been found between [1s3p] and [1s3d] and between [1s4s] and [1s3d] double-electron excitation edges, respectively. The importance of multielectron excitation in x-ray absorption spectra is discussed.

A simple potential model proposed for the elastic scattering of positrons off rare-gas atoms is used to compute low-energy phase shifts and differential scattering cross sections σ(θ) for positrons incident on ${}_{10}{}^{}{}_{}{}^{}\mathrm{Ne}$, ${}_{18}{}^{}{}_{}{}^{}\mathrm{Ar}$, and ${}_{36}{}^{}{}_{}{}^{}\mathrm{Kr}$ at energies 20, 3.4, and 6.67 eV, respectively. The calculated results for σ(θ) are in good agreement with currently available experimental values and are as reliable as the numbers obtained from much more elaborate calculations. It is pointed out that an important virtue of the present model is its simplicity.

The photoabsorption spectrum of the C iv ion has been obtained with the two laser-produced plasma technique. The 1s inner-electron and the 2s and 2p valence-electron absorption spectra have been measured. From the L-shell spectra the value of the line ion density in the 1${\mathit{s}}^2$2s and 1${\mathit{s}}^2$2p levels has been obtained and the measurement of the total inner-shell photoionization cross section has been derived. The absorption line profiles of the L-shell spectra have also been compared with the theories of line broadening due to the Stark effect.

The projectile energy loss for 7.5–25-MeV ${\mathrm{C}}^{6+,5+}$ and ${\mathrm{F}}^{6+}$ ions was measured for single collisions with He, Ne, Ar, and Kr as a function of the recoil-ion charge state and the projectile scattering. This energy loss was measured for collisions in which the projectile captured an electron and for those involving just direct ionization. We investigated and found a large average energy transfer (100–250 eV/electron) to the continuum electrons. A strong increase of the scattering angle with recoil-ion charge state was observed for both capture and direct ionization. The results imply that, for smaller impact parameters, higher recoil-ion charge states are produced and that higher energy losses are obtained. We observed a weak target-Z dependence of the energy loss. The results are compared with n-body classical-trajectory Monte Carlo calculations by Olson, semiclassical-approximation calculations by Schuch et al. [Nucl. Instrum. Methods Phys. Res. Sect. B 42, 566 (1989)], and the energy-deposition model.

We report measurements of the kinetic energy (${\mathit{E}}_{\mathit{k}}$) distributions of ${\mathrm{O}}^{\mathrm{-}}$ produced by low-energy electron impact (5.5–19.5 eV) on disordered multilayers of ${\mathrm{O}}_2$ physisorbed on a polycrystalline Pt substrate. The results confirm that dissociative electron attachment (DEA) proceeds via the formation of the ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$, ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$(I), and ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathit{x}}^{+}{}_{}{}^{}$(II) (x=g and/or u) states of ${\mathrm{O}}_2^{\mathrm{-}\mathrm{*}}$. We also find evidence for an additional resonance, namely the ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$(I), positioned at about 10 eV above the neutral ground state in the Franck-Condon region, and dissociating into ${\mathrm{O}}^{\mathrm{-}}$+O${(}^3$P). The measurements suggest that the autodetachment lifetimes of the ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$(I) and ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$(II) states may be longer than previously suggested. It is also observed that the effects of electron energy loss (EEL) in the solid prior to DEA, ${\mathrm{O}}^{\mathrm{-}}$ scattering in the solid after dissociation, and the charge-induced polarization energy of the solid, broaden the ${\mathit{E}}_{\mathit{k}}$ distributions, shift them to lower anion energies, and result in additional structure in them. The effects of EEL on the desorption dynamics of ${\mathrm{O}}^{\mathrm{-}}$ are estimated from high-resolution electron-energy-loss spectra and excitation functions for losses in the vicinity of the Schumann-Runge continuum of the physisorbed ${\mathrm{O}}_2$ molecules. We find indications for an enhancement of the optically forbidden X ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{\mathrm{-}}{}_{}{}^{}$→A ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$ transition, and observe that the gas-phase Rydberg bands, for energy losses above 7 eV, are not distinguishable in the condensed phase.

The method of 0° Auger spectroscopy was utilized to measure state-selective K-shell excitation in Li-like ${\mathrm{Ne}}^{7+}$ incident with 170-MeV on ${\mathrm{H}}_2$, He, ${\mathrm{CH}}_4$, Ne, and Ar. Interferences between first- and second-order mechanisms are searched for in the production of the doubly excited states 1s2${\mathit{p}}^2$ ${}_{}{}^2{}_{}{}^{}$D and 1s2${\mathit{p}}^2$ ${}_{}{}^2{}_{}{}^{}$S. The semiclassical approximation is applied to study time ordering of the double-excitation process. It is shown that time ordering is lost for the second-order amplitude so that it is unable to interfere with the first-order amplitude. The doubly excited state 1s2${\mathit{p}}^2$ ${}_{}{}^2{}_{}{}^{}$S is predominantly produced by the single-electron transition 1s→2s followed by configuration interaction with 1s2${\mathit{s}}^2$ ${}_{}{}^2{}_{}{}^{}$S. Discrepancies occur between theory and experiments as the state 1s2${\mathit{p}}^2$ ${}_{}{}^2{}_{}{}^{}$D is interpreted in terms of the independent dipole transitions 1s→2p and 2s→2p.

Coulomb and screening corrections to the amplitude for Delbrück scattering in the forward direction are calculated.

Spectra of L x rays emitted by 6- and 8-MeV/u Xe ions interacting with a variety of solid targets have been measured with a curved-crystal spectrometer. The spectra displayed an overall structure consisting of six strong peaks which were fairly well resolved for low-Z targets (${\mathit{Z}}_2$=3–6), but broadened into two featureless groups for higher-Z targets. The main components were identified as L${\mathrm{\alpha }}_1$ and L${\mathrm{\beta }}_1$ pairs associated with initial-state configurations having one to six L-shell vacancies. Detailed spectral analysis provided estimates of the average projectile charges and the average L- and M-electron populations inside the solids.

Theoretical photoionization spectra below the 2p threshold of the Be isoelectronic sequence from the ground and a few selected ${}_{}{}^1{}_{}{}^{}$S bound excited states are calculated using a B-spline-based configuration-interaction approach. The resonant structures of the doubly excited autoionization series following photoionization from different initial states are analyzed in detail in terms of various initial- and final-state multielectron interactions. In addition, our calculation has shown that the resonant widths vary smoothly as functions of the effective principal quantum number ν along the autoionization series and approach approximately an expected ${\nu }^{\mathrm{-}3}$ dependence as ν increases.

Galilean invariant cross sections were calculated for one-electron capture in collisions of ${\mathrm{B}}^{3+}$ with He at velocities between 0.063 and 0.63 a.u. The collision was described within the framework of the perturbed stationary-state approach with the potential-energy curves and nonadiabatic couplings computed with highly correlated configuration-interaction wave functions. A procedure was also proposed to incorporate Galilean invariance without the explicit calculation of translation factors and a method developed to solve the coupling integrals. Cross-section results are in good agreement with existing experimental and theoretical data.

The dissociation of CO caused by 1-MeV/amu ${\mathrm{F}}^{4+}$ impact has been studied using the coincidence time-of-flight technique. The kinetic energy released during the dissociation of ${\mathrm{CO}}^{\mathit{Q}+}$ into ion pairs ${\mathrm{C}}_1^{\mathit{q}}$+ and ${\mathit{O}}_2^{\mathit{q}+}$ was determined from the measured difference in the times of flight of the two charged fragments. The kinetic-energy distributions of ${\mathrm{CO}}^{2+}$ dissociating into ${\mathrm{C}}^{+}$ and ${\mathrm{O}}^{+}$ as a result of different impinging projectiles have been compared. These distributions shift towards higher kinetic-energy release values with increasing strength of interaction. A single Gaussian kinetic-energy distribution is in good agreement with the highly charged CO dissociation, while for doubly and triply charged CO, additional Gaussians are needed. While the Coulomb-explosion model approximately predicts the most likely value of a measured distribution, the widths of all distributions are grossly underestimated by the model. The measured widths of the distributions can be explained only by invoking the existence of potential-energy curves of the multiply charged ions that have steeper and shallower slopes as compared to the Coulombic curve. The reflection method was used to calculate the kinetic-energy release for ${\mathrm{F}}^{4+}$+CO→${\mathrm{CO}}^{2+\mathrm{*}}$ transitions to all known ${\mathrm{CO}}^{2+}$ states. The final kinetic-energy distribution was then fitted to the data in order to evaluate the weights of the different transitions. The calculated fit is in fair agreement with the measured one, although the high-energy tail of the measured distribution could not be accounted for, indicating that contributions from highly excited dissociating states or from curve crossings need to be included.

It is well known that cross sections for ionization of atoms by fast charged particles and by photons are related by the Bethe-Born theory. We employ this relationship to derive a corresponding relation for the ratio R of double to single ionization including the first two terms of the Bethe expansion. For sufficiently fast charged particles, where the second term can be ignored, the ratios as a function of ΔE—the energies transferred to the atom by the projectile—for ionization by charged particles ${\mathit{R}}_{\mathit{z}}$(ΔE) and by photons ${\mathit{R}}_{\gamma }$(ΔE) are equal: ${\mathit{R}}_{\mathit{z}}$(ΔE)=${\mathit{R}}_{\gamma }$(ΔE). In addition, a relation for the ratio of total charged-particle impact ionization cross sections to the photon ratio is derived. The results are compared with recent experimental data and various discrepancies are found and discussed.

Electron-transmission spectroscopy is used to observe structure in the electron-scattering cross section associated with the formation of temporary negative ions and channel-opening effects. A strong ‘‘family’’ resemblance is apparent among the resonances of the alkali metals. From published calculations and angular scattering studies, the lower-lying features are known with some confidence. Based on these, plausible assignments for some of the higher-lying resonances are put forth. We propose that the absence of resonances near the Cs 5 ${}_{}{}^2{}_{}{}^{}$D and possibly the Na 4 ${}_{}{}^2{}_{}{}^{}$P and 5 ${}_{}{}^2{}_{}{}^{}$P thresholds is associated with the negative polarizabilities of these excited states.

Absolute total-cross-section measurements have been performed on the ${\mathit{e}}^{\mathrm{-}\mathrm{-}}$${\mathrm{C}}_2$${\mathrm{H}}_2$ and ${\mathit{e}}^{\mathrm{-}}$-CO systems in the energy range 400–2600 eV. An apparatus with linear transmission technique was used. The estimated total experimental errors are about 5%. The results have been compared with available experimental and theoretical results. No previous data for e-${\mathrm{C}}_2$${\mathrm{H}}_2$ have been found in the literature for impact energies above 400 eV.