Distorted-wave calculations of the triply differential cross sections for electron-impact ionization of H, He, Ne, Ar, Kr, and Xe are presented for final-state electrons sharing ≤4 eV excess energy and for the coplanar, ${\mathrm{\theta }}_{12}$=π geometry. Results for H and He targets, presented briefly elsewhere [C. Pan and A. F. Starace, Phys. Rev. Lett. 67, 185 (1991)], are analyzed in greater detail and compared with available experimental and other theoretical results. In particular, for He targets the effects of exchange and of second-order capture processes are exhibited. These are shown to be of lesser importance than other short-range effects on the s-wave phase shifts of both incident and final-state continuum electrons for reproducing the experimentally observed target dependence of the electron angular distributions for H and He targets [P. Schlemmer, T. Rösel, K. Jung, and H. Ehrhardt, Phys. Rev. Lett. 63, 252 (1989)]. More approximate theoretical (e,2e) results for Ne, Ar, Kr, and Xe targets also show striking target dependences; they are compared with available experimental results.

The resonant transfer and excitation cross sections through the LMM transitions in collisions of chlorinelike ${\mathrm{Fe}}^{9+}$, ${\mathrm{Nb}}^{24+}$, and ${\mathrm{La}}^{40+}$ with ${\mathrm{H}}_2$ targets were calculated in impulse approximation using the multiconfiguration Dirac-Fock method. The effect of relativity reduces the total LMM resonance strength for ${\mathrm{La}}^{40+}$ by 29%. The angular distribution corrections at θ=90° increase the cross sections by an amount less than 10%. The present theoretical predictions for ${\mathrm{La}}^{40+}$ colliding with ${\mathrm{H}}_2$ are in reasonable agreement with the experimental observations.

We present the results of calculations for ${\mathit{e}}^{\mathrm{-}}$+${\mathrm{H}}_2^{+}$ scattering in the region below the first excited state. We employ three distinct and independent methods, close-coupling linear algebraic, effective-optical-potential linear algebraic, and R matrix, to examine the collision at the highest level of sophistication and to provide a valuable check on the results of a single technique. For the ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$ symmetries, we find strong interference effects between various autoionizing series, leading to significant variations of the resonance width with internuclear separation R. Such variations may have profound effects on such processes as photoionization, dissociation, and recombination. For the ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$ symmetries, we observe monotonic behavior of the width with R and find no evidence of strong interference effects or rapid changes.

Polarizabilities and photoionization cross sections are computed for the hydrides OH and HF. Finite basis sets are used, with no explicit recourse to continuum orbitals, and single-center expansions are avoided. The present method is based on an integral equation (dispersion relation) that relates the real polarizability on the imaginary frequency axis to the photoionization cross section. Many-body perturbation theory is used to compute the polarizabilities, and the perturbation expansion, which includes a total of 68 distinct diagrams to second order in the Coulomb interaction, is believed to contain all significant terms to that order. Thus there is a comprehensive inclusion of correlation effects, contrary to most molecular photoionization computations presented so far. The present results are compared with those of other computations, and with experiment in the case of HF.

We have studied the spin relaxation of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ nuclei due to collisions with Rb atoms at Xe pressures of 245–1817 Torr. Our results can be characterized by two parameters, the Rb${\mathrm{-}}^{129}$Xe velocity-averaged binary spin-exchange cross section 〈σv〉 and a rate ${\gamma }_{\mathit{M}}$ that characterizes spin relaxation due to van der Waals molecules. Our results complement earlier studies performed at Xe pressures of about 1 Torr and ${\mathrm{N}}_2$ pressures of 10–100 Torr. This work is useful for predicting spin-exchange rates between polarized Rb atoms and ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ nuclei.

The photoionization of krypton 4p, 4s, and 3d subshells has been studied theoretically from the 4p threshold and experimentally from the 3d threshold up to a photon energy of 260 eV. In converting the measured count rates of the 4p, 4s, and 3d main photoelectron lines into partial cross sections, we have used recent photoion yield measurements to estimate the contribution of multiple-excitation processes to the total photoabsorption cross section. Theoretical partial cross sections and angular asymmetry parameters have been calculated using the multichannel Dirac-Fock method. Eighteen leading single-excitation channels related to the 4p, 4s, 3d, and 3p hole configurations of the final ionic state were included. Relaxation was taken into account by using separately optimized initial- and final-state orbitals and by including all the resulting overlap integrals in the transition amplitudes. The relaxation effect was found to depend strongly on the photon energy in the near-threshold regions. For the 3d subshell the relaxation reduces the 3d cross section by 35–40 % at the maximum, whereas it is less significant for the 4p and 4s cross sections.

Total and single-differential cross sections for electron-impact ionizaton are calculated in a relativistic formulation for ions in the hydrogen isoelectronic sequence: Hi i, He ii, C vi, Ne x, Fe xxvi, and Ag xlvii. Transition amplitudes are evaluated in the two-potential distorted-wave approximation. Sets of different asymptotic charges are used to study the mutual screening of the primary and secondary electrons. Relativistic effects are investigated by taking the nonrelativistic limit and are found to increase the cross sections. Thomson’s scaling law along the isoelectronic sequence is also studied.

Secondary-electron energy spectra were measured for ${\mathrm{Ar}}^{\mathit{q}+}$ (q=9 and 16) and the H-like ions ${\mathrm{N}}^{6+}$, ${\mathrm{O}}^{7+}$, and ${\mathrm{Ne}}^{9+}$, incident on solid Cu surfaces at an angle of 10°. The impact energy was varied from 10q to 20q keV. Auger electrons were detected at various observation angles from 20° to 180° with respect to the incident beam. From the Doppler shift of the projectile Auger electrons, the L Auger electrons of argon and neon are found to be emitted from ions whose flight direction is parallel to the incident beam and the K Auger electrons of nitrogen, oxygen, and neon are observed to be emitted from deflected ions. Evidence is provided for incident ${\mathrm{Ne}}^{9+}$ and ${\mathrm{Ar}}^{16+}$ that the L shells are incompletely filled when the projectiles reach the surface. The data analysis is supported by model calculations.

The dependence of the atom-metal surface interaction potential on the response time of the metal electron gas is discussed. For an atom in its ground state, it is shown that the mirror-image potential of classical electrostatics can be retrieved if the metal response time in the Lifshitz formula is much shorter than the characteristic fluctuation time of the atom, whereas, for the opposite limit, the interaction potential of an atom in a spherically symmetric state is vanishingly small. For an atom in an excited state the interaction potential has additional terms that have the same dependence on the atom-surface separation, but it displays a resonant, dispersive character and may lead to attraction as well as repulsion of the atom.

We present secondary-electron spectra arising from collisions of ${\mathrm{N}}^{7+}$ ions with a Ni(110) target for kinetic energies ranging between 150 eV and 20 keV and also for different observation angles. The filling of the two K-shell holes in ${\mathrm{N}}^{7+}$ requires two consecutive KLL Auger processes, giving rise to a double structure in the KLL peak. The ratio of the intensities of the two KLL peaks depends on the collision energy as well as on the angle of observation. We show that this dependence can be explained by assuming that the KLL electrons are emitted after the projectile has penetrated the surface.

The isotope shifts in the resonance lines 4${\mathit{s}}_{1/2}$→4${\mathit{p}}_{1/2,3/2}$ in Ca ii have been measured for the isotopes ${}_{}{}^{40\mathrm{-}48}{}_{}{}^{}\mathrm{Ca}$ by fast-ion-beam collinear laser spectroscopy. Atomic many-body perturbation theory was then used to calculate the electronic factor for the field shift, giving F=-285(3) MHz/${\mathrm{fm}}^2$. The estimate of the uncertainty in F is based on the agreement at the level of 1% for the 4s and 4p hyperfine structures obtained using the same wave functions which include core polarization and pair correlation to all orders. The theoretical value is in excellent agreement with the result F=-283(6) MHz/${\mathrm{fm}}^2$ obtained from a King-plot procedure combining the experimental isotope shifts with earlier data. In combination with the electron scattering data for the isotope pair ${}_{}{}^{40,48}{}_{}{}^{}\mathrm{Ca}$, the present results are used to extract a set of δ〈${\mathit{r}}^2$〉 values for all the isotopes, independent of the muonic data and earlier optical isotope-shift measurements.

The x-ray absorption of transition metals from Cr to Zn is examined in the energy region of K+L double photoabsorption. A variational procedure is developed to extract correlated components from pairs of spectra. Applied to absorption spectra taken at different sample temperatures, the procedure is used to suppress the extended x-ray-absorption fine-structure oscillations that pervade the K+L region in this range of elements. A relative sensitivity of 2×${10}^{\mathrm{-}3}$ to 3×${10}^{\mathrm{-}4}$ of the absorption coefficient, depending on the sample quality, is achieved. No significant features attributable to multiple photoexcitation are found in the spectra on that level, so that previous reports of K+L edges for Co, Ni, and Zn are not confirmed.

We have located the ${(}^2$D°)4p’ ${}_{}{}^3{}_{}{}^{}$F and ${(}^2$D°)3p’ ${}_{}{}^3{}_{}{}^{}$P autoionizing states of atomic oxygen and measured the autoionization-dominated lifetimes for the ${(}^2$D°)3p’ ${}_{}{}^{1,3}{}_{}{}^{}$P, and ${(}^2$D°)3p’ ${}_{}{}^3{}_{}{}^{}$D${,}^3$F states. In addition, we have measured transition strengths for the ${(}^4$S°)3p ${}_{}{}^3{}_{}{}^{}$P to ${(}^2$D°)3s’ ${}_{}{}^3{}_{}{}^{}$D° and ${(}^2$D°)3s’ ${}_{}{}^3{}_{}{}^{}$D° to ${(}^2$D°)3p’ ${}_{}{}^{1,3}{}_{}{}^{}$P${,}^3$D${,}^3$F transitions, and characterized the 2${\mathit{p}}^4$ ${}_{}{}^3{}_{}{}^{}$P to ${(}^4$S°)3p ${}_{}{}^3{}_{}{}^{}$P two-photon resonance for saturating light intensities. In making these original measurements, we use a variety of multiphoton-ionization methods, including Rabi-oscillation and damped-Rabi-oscillation methods.

Double-resonance spectroscopy via several rotational levels of the ${\mathrm{N}}_2$ ${\mathit{a}}^1$${\mathrm{\Pi }}_{\mathit{g}}$, v’=5 state has been used to probe the rotational structure of a complex autoionizing resonance observed just below the ${\mathit{X}}^2$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$, ${\mathit{v}}^{+}$=1 threshold. A multichannel-quantum-defect-theory (MQDT) analysis confirms that the complex resonance is produced by the interaction of two interloping states with the np and nf Rydberg series converging to the ${\mathit{X}}^2$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$, ${\mathit{v}}^{+}$=1 limit. The quantum defects of the interlopers and their interaction strengths with the two Rydberg series are determined from fits of the MQDT model to the energies of the peaks observed in the complex resonance. The experimentally determined interaction parameters and those available from ab initio calculations are in fair agreement. The present results complete the interpretation of the photoionization spectrum of ${\mathrm{N}}_2$ in the energy region between the ${\mathit{X}}^2$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$, ${\mathit{v}}^{+}$=0 and 1 thresholds.

We discuss the spectrum of light scattered by N atomic dipoles. We present examples illustrating the nature of contributions proportional to N and ${\mathit{N}}^2$ in ‘‘coherent’’ and ‘‘incoherent’’ forward and side scattering. We use a detector-based formalism that differs in some respects from the formalism of Sundaram and Milonni [Phys. Rev. A 41, 6571 (1990)].

Nine L x-ray emission lines of xenon (Z=54) in the gas phase were measured in fluorescence. The spectra were obtained on a double-crystal spectrometer using a conventional x-ray tube for primary excitation. The binding energies of the L subshells were obtained using the experimental x-ray photoelectron-spectroscopy (XPS) ionization energies of the final states and found to be in agreement with earlier XPS measurement. The K-shell binding energy was also determined. The transition energies, level energies, and widths were analyzed with respect to available experimental and theoretical data. Discrepancies between experiment and theory are discussed in terms of dynamical relaxation and decay. It is suggested that this discrepancy can be mended by using the many-body approach such as the Green’s-function method, which treats such strong correlations in a consistent way.

We report results of a combined theoretical and experimental investigation that uses Stark spectroscopy of high-lying Rydberg states to measure accurately zero-field atomic parameters. Improved values for the binding energies of the 11 ${}_{}{}^2{}_{}{}^{}$S, 12 ${}_{}{}^2{}_{}{}^{}$S, and ${10}^2$D states of sodium are presented. These results are combined with previous data in a global least-squares fit to obtain improved quantum-defect parameters for the sodium ${}_{}{}^2{}_{}{}^{}$S and ${}_{}{}^2{}_{}{}^{}$D manifolds. Using previous precision optical data, the present results, and the quantum-defect expansion, we obtain an improved value for the ionization limit of neutral sodium: ${\mathit{E}}_{\mathrm{ion}}$=41 449.451(2) ${\mathrm{cm}}^{\mathrm{-}1}$. The consequences of the improved ionization energy on the quantum-defect expansion parameters of the ${}_{}{}^2{}_{}{}^{}$P states are also discussed and values are obtained from fits to the available data.

Hartree-Fock calculations on restricted regions of the ground-state potential-energy surface of ${\mathrm{B}}_3$ are carried out. The correlation energy is calculated by using one-body and two-body density functionals. The results obtained with all those functionals are very similar, predicting a stable molecule with a potential-energy surface that shows two minima that differ by about 1.3 eV. The present results are in good agreement with recent calculations of Hernandez and Simons [J. Chem. Phys. 94, 2961 (1991)], who used a very different method in which correlation energy is obtained by extended multiconfiguration calculations.

We examine the dynamics of the wave function of a hydrogen Rydberg electron for the case in which the Rydberg states are created by two temporally separated laser pulses. We study the influence of the phase difference between the two pulses. For instance, the electron can make one orbit as a Rydberg wave packet created by the first laser pulse, after which it is sent back to the ground state by the second pulse. The time dependence of the wave packet created by the first pulse can be probed by examination of the total population after the two-pulse sequence. The influence of the relative phase of the two pulses on the total population can be seen as Ramsey fringes. We describe a scheme of wave-packet detection based on this effect.

The structure of the eigenstates of a hydrogen atom in parallel uniform electric and magnetic fields is investigated using high-order classical perturbation theory. The Kustaanheimo-Stiefel transformation is first used to convert the problem into an anharmonically perturbed four-dimensional isotropic oscillator. A canonical transformation to a set of extended ‘‘Lissajous’’ action-angle variables is then introduced that considerably simplifies the perturbation expansion, leading to a simple and compelling classification scheme for the eigenstates. Extended Lissajous action-angle variables allow the construction of rotational energy surfaces, which provide a compact geometrical picture that captures important details of the energy-level structure of the system.