We solve the Kohn-Sham equations using the Zhao-Parr constraint potential within the Levy constrained-search method. Accurate exchange-correlation potentials, orbital energies, and components of the total energy including the Kohn-Sham kinetic energy ${\mathit{T}}_{\mathit{s}}$, the kinetic-energy contribution ${\mathit{T}}_{\mathit{c}}$ to the exchange-correlation energy, and the exchange-correlation energy are calculated for the neutral atoms He through Ar. Reference densities used in the Zhao-Parr constraint potential are calculated from accurate, correlated, nonrelativistic wave functions. The exchange-correlation potentials exhibit characteristic intershell peaks, one for the atoms Li through Ne and two for the atoms Na through Ar.

We present experimental energy-level positions for Ba high-l Nsnl double Rydberg states with N=8 (n=13–15, l⩾7) and N=9 (n=13–15, l⩾7). These data as well as previously reported measurements for N=7 (n=12–15, l⩾5) and N=10 (n=13–15, l⩾10) are parametrized in order to yield values for the ${\mathrm{Ba}}^{+}$ Ns effective dipole ${\mathrm{\alpha }}_{\mathrm{d}}^{\prime }$ and quadrupole ${\mathrm{\alpha }}_{\mathrm{q}}^{\prime }$ polarizabilities. The obtained ${\mathrm{\alpha }}_{\mathrm{d}}^{\prime }$ values are 1.25(5)×${10}^3$, 7.05(4)×${10}^3$, 2.95(4)×${10}^4$, 9.39(15)×${10}^4$ in ${\mathrm{a}}_0^3$ units and the ${\mathrm{\alpha }}_{\mathrm{q}}^{\prime }$ values are 1.7(8)×${10}^4$, 1.8(2)×${10}^5$, -1.0(2)×${10}^6$, -1.0(2)×${10}^7$ in ${\mathrm{a}}_0^5$ units for N=7, 8, 9, and 10, respectively. The ${\mathrm{\alpha }}_{\mathrm{d}}^{\prime }$ evolution with N is found to follow a ${\mathrm{N}}^{\mathrm{*}6.9\left(1\right)\mathrm{}}$ power law, while calculated static polarizabilities present somewhat lower power dependence. From this small difference it is not possible to appreciate the importance of nonadiabatic effects between the two asymmetrically excited electrons. On the other hand, the larger discrepancies appearing between the calculated static and fitted quadrupole polarizabilities show clear evidence of nonadiabatic effects. Particularly the negative ${\mathrm{\alpha }}_{\mathrm{q}}^{\prime }$ sign for N⩾9 is attributed to the increasing strength of dynamical effects on the Ns core electron caused by the motion of the outer high-l electron. It gives evidence of the increasing importance of nonadiabatic radial correlation between two planetary electrons when the Ns inner electron is sufficiently radially extended to be characterized as an inner Rydberg electron without, nevertheless, any appreciable overlapping with the outer electron.

Fine structure in the ${}_{}{}^2{}_{}{}^{}$F Rydberg states of indium has been studied by optical-microwave double-resonance spectroscopy. Microwave transitions between the neighboring levels of the ${}_{}{}^2{}_{}{}^{}$${\mathit{F}}_{5/2}$ and ${}_{}{}^2{}_{}{}^{}$${\mathit{F}}_{7/2}$ Rydberg series have been measured for the range of n=35, 36, and 39–41. The experimental results show that the fine structure of the ${}_{}{}^2{}_{}{}^{}$F states is inverted. The observed inversion in the fine structure is found to be closely correlated with a long-range interaction between the inner core and the valence electron of the atom.

Ab initio calculations of the position of the 4s4${\mathit{p}}^2$ ${}_{}{}^4{}_{}{}^{}$P term in ${\mathrm{Ca}}^{\mathrm{-}}$ are described that take the interaction with the core into account in two different ways: one by means of a model potential using a spline basis and the other by an explicit multiconfiguration Hartree-Fock calculation. The calculated electron affinities relative to the 4s4p ${}_{}{}^3{}_{}{}^{}$P term are in good agreement but differ from experiment. The model potential result is in somewhat better agreement with experiment if the energy is interpreted relative to the ${\mathrm{Ca}}^{2+}$ ground state. Possible reasons for the discrepancy are discussed.

The now classic optimized-effective-potential (OEP) approach of Sharp and Horton [Phys Rev. 90, 317 (1953)] and Talman and Shadwick [Phys. Rev. A 14, 36 (1976)] seeks the local potential that is variationally optimized to best approximate the Hartree-Fock exchange operator. The resulting OEP can be identified as the exchange potential of Kohn-Sham density-functional theory. The present work generalizes this OEP approach to treat the correlated case, and shows that the Kohn-Sham exchange-correlation potential is the variationally best local approximation to the exchange-correlation self-energy. This provides a variational derivation of the equation for the exact exchange-correlation potential that was derived by Sham and Schlüter using a density condition. Implications for an approximate physical interpretation of the Kohn-Sham orbitals are discussesd. A correlated generalization of the Sharp-Horton–Krieger-Li-Iafrate [Phys Lett. A 146, 256 (1990)] approximation of the exchange potential is introduced in the quasiparticle limit.

We have constructed a beam-laser lifetime-measuring apparatus and tested it by measuring the well known lifetime of the v=0 level of the ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$ state of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}_2^{+}{}_{}{}^{}$. Our result of 61.8(5) ns is in excellent agreement with previous high-precision measurements. Employing this technique we performed measurements of the lifetimes of the four lowest vibrational levels of the B ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ state of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}_{}^{16}{}_{}{}^{}$${\mathrm{O}}^{+}$. The results are (in ns) 69.5(6), 72.4(5), 75.2(5), and 78.0(8) for v=0, 1, 2, and 2, respectively.

Accurate ab initio multiconfigurational-Dirac-Fock (MCDF) calculations of the lifetimes of the spin-forbidden 2${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$–2s2p ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$ transition and the allowed 2${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$–2s2p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ transition in Be-like ions have been performed. The importance of the inclusion of the Breit interaction to obtain accurate fine-structure splittings and mixing coefficients is discussed and the noted discrepancy between the length and velocity gauges for the intercombination line in the lighter ions is addressed. Different optimization procedures are evaluated. For C iii the experimental intercombination transition rate has been measured to be 121.9 ${\mathrm{s}}^{\mathrm{-}1}$ with an accuracy of 6%. The current calculation gives 100.3±4 ${\mathrm{s}}^{\mathrm{-}1}$, in agreement with other recent calculations.

We are investigating the hyperfine quenching of 1s2p ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_0^{\mathit{o}}$ for the three heliumlike ions ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}_{}^{7+}{}_{}{}^{}$, ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}_{}^{9+}{}_{}{}^{}$, and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}_{}^{11+}{}_{}{}^{}$ in the multiconfigurational Hartree-Fock-Breit-Pauli scheme. The configuration expansions are generated with the active-space method and are increased in a systematic way, allowing the convergence of the calculated parameters to be studied. A careful comparison is done with the pioneering work of Mohr using a perturbation approach [Beam-Foil Spectroscopy, Atomic Structure and Lifetimes, edited by I. Sellin and D. Pegg (Plenum, New York, 1976), Vol. 1, pp. 97–103]. In the present calculations the orbital and spin-dipole magnetic contributions, which were previously neglected, are added to the dominant Fermi contact interaction term and a detailed analysis of the hyperfine induced transition rate is done in order to learn how to get an accurate description of the property in the multiconfiguration Hartree-Fock-Breit-Pauli approximation.

An exact expression in terms of density matrices (DM) is derived for δF[n]/δn(r), the functional derivative of the Hohenberg-Kohn functional. The derivation starts from the differential form of the virial theorem, obtained here for an electron system with arbitrary interactions, and leads to an expression taking the form of an integral over a path that can be chosen arbitrarily. After applying this approach to the equivalent system of noninteracting electrons (Slater-Kohn-Sham scheme) and combining the corresponding result with the previous one, an exact expression for the exchange-correlation potential ${\mathit{v}}_{\mathrm{xc}}$(r) is obtained which is analogous in character to that for δF[n]/δn(r), but involving, besides the interacting-system DMs, also the noninteracitng DMs. Equating the former DMs to the latter ones, we reduce the result for the exact ${\mathit{v}}_{\mathrm{xc}}$(r) to that for an approximate exchange-only potential ${\mathit{v}}_{\mathit{x}}$(r). This leads naturally to the Harbola-Sahni exchange-only potential.

We employ a quantum Monte Carlo method for the oscillator strength to the computation of the controversial 2 ${}_{}{}^2{}_{}{}^{}$S→2 ${}_{}{}^2{}_{}{}^{}$P transition of the Li atom. We use simple trial functions that are optimized for accuracy in coordinate expectation values as well as the energy. We obtain an oscillator strength of 0.7431(6), in very good agreement with the experimental value of 0.7416(12) [A. Gaupp, P. Kuske, and H. J. Andrä, Phys. Rev. A 26, 3351 (1982)]. The precision obtained here, an order of magnitude greater than that of our previous value [R. N. Barnett, P. J. Reynolds, and W. A. Lester, Jr., Int. J. Quantum Chem. 42, 837 (1992)] shows that the quantum Monte Carlo oscillator strength unambiguously supports the experimental value over recent theoretical values.

The extreme ultraviolet photoabsorption spectra of neutral to three-times-ionized strontium have been recorded in a comprehensive series of experiments with the dual laser-produced plasma technique. Striking differences were found in the spectra, which can be attributed to the transfer of oscillator strength from 3d→np to 3d→nf transitions at ${\mathrm{Sr}}^{2+}$ due to nf wave-function contraction. In Sr and ${\mathrm{Sr}}^{+}$, 3d→5p transitions dominate; in ${\mathrm{Sr}}^{2+}$, 3d→nf transitions are most intense, while in ${\mathrm{Sr}}^{3+}$ the 4p subshell opens and 3d→4p transitions are the strongest features. Partial cross sections for 3d→ɛf and 3d→ɛp photoionization were calculated and compared with experiment.

Electron capture in collisions of ${\mathrm{N}}^{+}$ ions with He atoms is studied by using a molecular representation. Because excitation channels to ${\mathit{N}}^{+\mathrm{*}}$${(}^3$D) lie very close to the electron-capture channels, electron capture by the ground ${\mathrm{N}}^{+}$${(}^3$P) state, which strongly couples with ${\mathrm{N}}^{+\mathrm{*}}$${(}^3$D) excitation channels, is dominant below 6 keV. As the energy increases, electron capture by metastable ${\mathrm{N}}^{+\mathrm{*}}$${(}^5$S) ions becomes dominant due to a smaller energy defect. The excitation cross section to the ${\mathrm{N}}^{+\mathrm{*}}$${(}^3$D) states and the cross section of electron capture interfere with each other, showing complex patterns of in-phase and out-of-phase oscillations that depend on the energies.

We report medium-resolution [0.025 nm full width at half maximum (FWHM)] electron-impact-induced emission spectra of CO for 20-, 100-, and 200-eV impact energies. The emission spectra correspond to the extreme-ultraviolet transitions from the B ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0), ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0), and E ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }$(0) vibronic states to the X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0) ground state. The present measurements are carried out at 20 times higher spectral resolution (to separate the many blended components) compared to our previous measurements, which were at a spectral resolution of 0.5 nm FWHM. The emission cross sections corresponding to the B ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0) →X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0), C ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0)→X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0), and E ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }$(0)→X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0) resonance transitions were measured. In addition, excitation functions (0–1 keV) extending well into the Born region have been measured for the strong transitions [B ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0)→X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0) and ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0)→X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$(0)] and oscillator strengths have been determined, using a modified-Born-approximation analytic fit to the measured excitation function.

Explorations of the classical phase space for ion collisions with circular Rydberg atoms are presented. Intermediate-energy capture and ionization processes are studied through the numerical integration of Newton’s equations of motion and through the graphical depiction of the outcomes of large numbers of trajectories. Maps which correlate initial conditions with final outcomes are used to identify zones of parameter space leading to Thomas capture, direct capture, binary-encounter ionization, saddle-point ionization, and ionization by S superpromotion (E. A. Solov’ev, Zh. Eksp. Teor. Fiz. 81, 1681 (1981) [Sov. Phys. JETP 54, 893 (1981)]). Charge-transfer channels in which the electron passes once or three times through the midplane between the nuclei are shown to occur in separate zones of parameter space over the entire range of projectile speeds above the mean velocity of the target electron.

Absolute cross sections for photoionization of isotropically populated Ba(6s6p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$) to each accessible final J state (0, 1, and 2) have been determined from threshold to 370 nm using spectra obtained with four different combinations of linear and circular polarizations of the exciting and ionizing radiation. The effects of dealignment due to hyperfine interaction of the nuclear spin I=3/2 isotopes of barium have been taken into account. The results are generally in good agreement with R-matrix predictions of shapes and positions of autoionizing resonances as well as the magnitudes of the background (nonresonance) cross sections, but there are some discrepancies with oscillator strengths of the autoionizing states. It is shown that, to obtain the correct magnitude of the background cross section theoretically, the inclusion of electron correlation effects in the wave functions of both initial and final states is required. Data are also presented that verify the equivalence of obtaining the total photoionization cross section by properly combining two sets of data, each acquired with a different angle between linear polarization vectors, e.g., parallel and perpendicular, or by making a single measurement with the angle set at the ‘‘magic’’ angle, 54.7°.

Optical emissions in single-collision, beam-beam reactions of fast (3–22-eV translational energy) O${(}^3$P) atoms with ${\mathrm{C}}_2$${\mathrm{H}}_2$ have been measured in the wavelength range 300–850 nm. Two features were observed, one with a peak wavelength at 431 nm, corresponding to the CH A ${}_{}{}^2{}_{}{}^{}\mathrm{X}$ ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathrm{r}}^{}{}_{}{}^{}$ transition, and a second weaker emission in the range 380–400 nm corresponding to the B ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{}^{\mathrm{-}}{}_{}{}^{}$→X ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathrm{r}}^{}{}_{}{}^{}$ transition. Both the A→X and B→X emissions were fit to a synthetic spectrum of CH(A) at a vibrational temperature ${\mathit{T}}_{\mathit{v}}$ of 10 000 K (0.86 eV) and a rotational temperature ${\mathit{T}}_{\mathit{r}}$ of approximately 5000 K (0.43 eV); and CH(B) to ${\mathit{T}}_{\mathit{v}}$=2500 K (0.22 eV) and ${\mathit{T}}_{\mathit{r}}$=1000 K (0.09 eV). The energy threshold for the A→X emission was measured to be 7.3±0.4 eV (lab) or 4.5±0.2 eV (c.m.). This agrees with the energy threshold of 7.36 eV (lab) for the reaction O${(}^3$P)+${\mathrm{C}}_2$${\mathrm{H}}_2$→CH(A)+HCO.

The process of radiative electron capture (REC) in relativistic collisions of high-Z ions with low-Z gaseous and solid targets is studied experimentally and theoretically. The observed x-ray spectra are analyzed with respect to photon angular distributions as well as to total K-REC cross sections. The experimental results for angle-differential cross sections are well reproduced by exact relativistic calculations which yield significant deviations from standard ${\sin }^2$θ distributions. Total cross sections for K-REC are shown to follow a simple scaling rule obtained from exact relativistic calculations as well as from a nonrelativistic dipole approximation. The agreement between these different theoretical approaches must be regarded as fortuitous, but it lends support to the use of the nonrelativistic approach for practical purposes.

We present results for the photoionization of ground and excited S states of two-electron systems by x-ray photons. The method uses the asymptotic formulation of Dalgarno and Stewart [Proc. Phys. Soc. London 76, 49 (1960)] with highly correlated Frankowski-Pekeris–type wave functions for N ${}_{}{}^1{}_{}{}^{}\mathrm{S}$ and N ${}_{}{}^3{}_{}{}^{}\mathrm{S}$ initial states. The calculations show a smaller ratio of double-to-single photoionization R for triplet states due to the spatial antisymmetry of the wave function near the nucleus. We find an asymmetric population of photoion satellite states and provide expressions for the asymptotic single and total photoionization, and R as a function of nuclear charge. We also make predictions for the differential double photoionization cross sections in the extreme energy sharing case when one electron is ejected with zero energy.

Angular distributions from 45° to 135° in 15° intervals of LMM Auger electrons produced by 1.2-MeV and 1.8-MeV ${\mathrm{He}}^{+}$-ion bombardment of argon, methyl chloride (${\mathrm{CH}}_3$Cl), and hydrogen sulfide (${\mathrm{H}}_2$S) have been measured. The LMM total Auger yields were measured at 1.8-eV resolution with an experimental probable error not exceeding 9%. The results revealed that the angular distributions of the LMM total Auger yields of Ar, Cl, and S were isotropic at these bombarding energies.

We report an experimental study of the single-quantum annihilation of positrons in a number of elements having atomic numbers between 49 and 90, utilizing a monoenergetic positron beam. Measurements were made of the differential cross sections for the forward direction for the K, L, and M atomic shells in targets of Th, Pb, Au, Hf, Gd, and In, having thicknesses that vary between 2.7 and 4.4 mg/${\mathrm{cm}}^2$. A shielded HPGe detector of high relative photopeak efficiency was used for recording the photon spectrum. Values for the individual atomic shells were obtained in the positron kinetic-energy range 1.02–2.24 MeV. It was observed that the differential cross sections measured for the forward direction varied with energy for each major shell almost alike so that the shell ratios appeared to remain constant while the positron energy varied. The dependence of the cross section on the atomic number Z of the target element was tested for each of the major shells at various energies of measurement. It was seen that the cross sections follow a ${\mathit{Z}}^{\nu }$ relation with ν≊5.1 as the exponent for the K shell. For the higher shells, the exponent is approximately 6.4, which is significantly larger. It was also noted that this pattern is fairly independent of the positron energy. The results on the Z dependence are seen to be clearly at variance with the most updated theoretical predictions.