Measurements of the 1s2${\mathit{p}}^1$${\mathit{P}}_1$→1${\mathit{s}}^{2\mathrm{}1}$${\mathit{S}}_0$, 1s2${\mathit{p}}^3$${\mathit{P}}_2$→1${\mathit{s}}^{2\mathrm{}1}$${\mathit{S}}_0$, 1s2${\mathit{p}}^3$${\mathit{P}}_1$→1${\mathit{s}}^{2\mathrm{}1}$${\mathit{S}}_0$, and 1s2${\mathit{s}}^3$${\mathit{S}}_1$→1${\mathit{s}}^{2\mathrm{}1}$${\mathit{S}}_0$ transitions in heliumlike krypton (${\mathrm{Kr}}^{34+}$) have been made on the Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory. The measurements were performed using a high-resolution crystal spectrometer and an accuracy of about 30 ppm was achieved. Unlike earlier measurements, our results are in good agreement with recent theoretical predictions. © 1996 The American Physical Society.

The 2s-2${\mathit{p}}_{3/2}$ transition energies in Li-like through F-like uraniums are calculated using the relativistic configuration-interaction method with B-spline basis functions. These calculations are based on the relativistic no-pair Hamiltonian, which includes both the Coulomb and retarded Breit interactions. Davidson’s method [E. R. Davidson, J. Comput. Phys. 17, 87 (1975)] is employed to solve the eigenvalue problem for the lowest few eigenenergies and eigenfunctions. Quantum electrodynamic and mass polarization corrections are also calculated. Good agreement with experiment for all uranium ions is found. © 1996 The American Physical Society.

Based on the constrained-search formulation of a coupled Hamiltonian, new formulas are given involving the correlation-energy density functional ${\mathit{E}}_{\mathit{c}}$[ρ] and its kinetic component ${\mathit{T}}_{\mathit{c}}$[ρ], starting from two relations of Levy and Perdew. Consequences are examined of assuming (following earlier authors) the existence of a Taylor series expansion of ${\mathit{E}}_{\mathit{c}}^{\lambda }$[ρ] in the coupling parameter λ. If one truncates the series at the linear term, one finds that ${\mathit{E}}_{\mathit{c}}$[ρ] and ${\mathit{T}}_{\mathit{c}}$[ρ] are homogeneous of degree zero with respect to coordinate scaling, and if local, they are homogeneous of degree one in the density scaling. More generally, it is shown that ${\mathit{E}}_{\mathit{c}}$[ρ] and ${\mathit{T}}_{\mathit{c}}$[ρ] are linear combinations of homogeneous functionals of different specific degrees in coordinate scaling: 0,-1,-2,-3,...,(1-n),... . If the functionals also are local, both ${\mathit{E}}_{\mathit{c}}$[ρ] and ${\mathit{T}}_{\mathit{c}}$[ρ] are combinations of functionals 〈${\mathrm{\rho }}^{\mathit{k}}$〉 homogeneous in ρ of degrees k=1,2/3,1/3,0,...,(4-n)/3,... . For atoms and molecules, k≥0, and so ${\mathit{E}}_{\mathit{c}}$ and ${\mathit{T}}_{\mathit{c}}$ take the form ${\mathit{X}}_{\mathit{c}}$[ρ]=aN+b∫${\mathrm{\rho }}^{2/3}$(r)${\mathit{d}}^3$r+c∫${\mathrm{\rho }}^{1/3}$(r) ${\mathrm{d}}^3$r+d, where a, b, c, and d are constants to be determined. Numerical tests are given that demonstrate the effectiveness of such series of local functionals. We also give definitions of density scaling, coordinate scaling, and homogeneities, and relations among them. © 1996 The American Physical Society.

In isoelectronic sequences, transition wavelengths ordinarily move rapidly to shorter wavelengths as Z increases. However, it has been predicted that a particular sequence of magnetic dipole (M1) transition wavelengths for the Ti-like ions, ${\mathrm{Xe}}^{+32\mathrm{}}$ through ${\mathrm{U}}^{+70\mathrm{}}$, remain relatively constant in the 320–400-nm range. In the present paper we extend the experimental identifications of the Ti-like M1 transitions from Ba and Xe to Nd (${\mathrm{Nd}}^{+38\mathrm{}}$) and Gd (${\mathrm{Gd}}^{+42\mathrm{}}$) to verify this behavior. Using the newly acquired wavelengths to adjust atomic parameters, we have also calculated improved wavelengths for all such M1 transitions between Xe (Z=54) and Os (Z=76). © 1996 The American Physical Society.

We performed line profile measurements of the 2s-2p resonance transitions in B III in order to test quantum-mechanical (close-coupling) theory. The experiment was carried out using the well-diagnosed gas-liner pinch discharge where plasma parameters are determined independently by 90° Thomson scattering. The experimental Stark widths are about twice the five-state close-coupling results. However, we find good agreement with semiclassical calculations in the electron-impact approximation. © 1996 The American Physical Society.

The frequency and the angular distributions of photons emitted in the bremsstrahlung process of a 0.2–10 keV electron in collision with Ba are calculated for the photon frequencies above the 4d threshold: ω=100–200 eV. The polarizational bremsstrahlung is taken into account. A simple method is described for the approximate calculation of the polarizational bremsstrahlung cross section. This method is particularly efficient in the case, when the many-electron correlations are important. ©1996 The American Physical Society.

Absolute optical emission cross sections have been measured for the second-positive band system of ${\mathrm{N}}_2$, C${\mathrm{}}^3$${\mathrm{\Pi }}_{\mathit{u}}$(v′)→B${\mathrm{}}^3$${\mathrm{\Pi }}_{\mathit{g}}$(v″), for v′=0,1,2,3,4 and v″ as large as 9 produced by electron impact with the nitrogen molecule for incident-electron energies from threshold up to 600 eV. The relative cross sections for each v′ family are in good agreement with the theoretical values. From the measured optical emission cross section, the apparent excitation cross sections for the v′=0,1,2,3,4 vibrational levels of the C${\mathrm{}}^3$${\mathrm{\Pi }}_{\mathit{u}}$ electronic states are determined. A comparison of these apparent cross sections with the relative direct excitation cross sections predicted by the Franck-Condon principle suggests that the population of the C${\mathrm{}}^3$${\mathrm{\Pi }}_{\mathit{u}}$ state in an electron-beam experiment for the v′=0,1, and 2 levels is primarily due to direct excitation with minor contributions from cascade. For the v′=3 and 4 levels, the direct excitation cross sections are much smaller so that a larger percentage population is attributed to cascade. The relative intensities of the various (v′,v″) bands in the electron-beam experiments are also compared with those observed in a dc discharge. © 1996 The American Physical Society.

We develop a theoretical description of the anisotropic interaction between a Rydberg electron and an ionic core. An adiabatic formulation expresses the anisotropic nature of the interaction through angular-momentum operators of the core and the Rydberg electron. Terms with odd tensorial structure, such as a vector hyperpolarization proportional to L${\to }_{\mathit{c}}$⋅l→, emerge in the long-range potential. Computed energies of neon n=10 Rydberg states are compared with recent experimental measurements. The vector term improves agreement between theory and experiment. The vector hyperpolarizability is calculated explicitly, along with some standard polarizabilities of ${\mathrm{Ne}}^{+}$. © 1996 The American Physical Society.

The nonlocal resonance model developed earlier for the description of low-energy inelastic and reactive electron-HCl collisions has been adapted to the electron-HBr collision system. The parameters of the model have been determined by fitting the eigenphase sum in the fixed-nuclei approximation to the data of an ab initio R-matrix calculation of Morgan, Burke, and collaborators. The Schwinger-Lanczos method has been employed to solve the nuclear scattering problem with a nonlocal, complex, and energy-dependent effective potential. Fully converged cross sections have been obtained on a dense grid of energies for many vibrational excitation, deexcitation, and dissociative channels in both HBr and DBr. The computed cross sections are generally in good agreement with experiment as far as data are available. © 1996 The American Physical Society.

Double-differential cross sections (DDCS’s) for the production of binary encounter electrons (BEE’s) were measured for collisions of 30-MeV ${\mathrm{O}}^{\mathit{q}+}$ projectiles with ${\mathrm{H}}_2$, He, ${\mathrm{O}}_2$, Ne, and Ar targets with q=4–8 and an electron ejection angle of θ=0° with respect to the beam direction. Particular interest focused on (a) the evaluation of the contributions of the different electron subshells of the multielectron targets, ${\mathrm{O}}_2$, Ne, and Ar; (b) the study of the well-known enhancement of the BEE DDCS’s with decreasing projectile charge-state q; here this dependence was tested for higher collision energies and new targets; (c) the study of the dependence of the BEE peak energy on the particular target and projectile charge state. Results were analyzed in terms of the impulse approximation, in which target electrons in the projectile frame undergo 180° elastic scattering in the field of the projectile ion. The electron scattering calculations were performed in a partial-wave treatment using the Hartree-Fock model. Good agreement with the data was found for the ${\mathrm{H}}_2$ and He targets, while for the multielectron targets ${\mathrm{O}}_2$, Ne, and Ar only electrons whose velocity was lower than the projectile velocity needed to be included for good agreement. All measured BEE DDCS’s were found to increase with decreasing projectile charge state, in agreement with other recent BEE results. The BEE peak energies were found to be independent of the projectile charge state for all targets utilized. © 1996 The American Physical Society.

In this work the cross section for the coincident detection of two electrons following double ionization of helium by fast electrons is analyzed. Structures arising in cross sections are associated with ionization mechanisms. The role of electronic correlations is elucidated. The theory is compared with available experimental data and suggestions for future experiments are made where results can be analyzed in terms of generalized asymmetry parameters and directly linked with well studied asymmetry parameters for double photoionization. Further, a method of calibrating relative (e,3e-1e) cross sections to double photoionization cross sections is proposed. © 1996 The American Physical Society.

The simple effective potential characteristic of the interaction of a slowly moving charged particle with a charged or neutral system in the nonretardation region (typically 5≲r/${\mathit{a}}_0$≲100) has, in addition to the α(0)/${\mathit{r}}^4$ static polarization potential and perhaps a Coulomb term, a ‘‘nonadiabatic’’ term of the form 3${\mathit{a}}_0$${\mathit{e}}^2$β(0)/${\mathit{r}}^6$. In the retardation region (r/${\mathit{a}}_0$≳137), there appears a term proportional to 1/${\mathit{r}}^5$, which is presumed to be a correction to the interaction of the charged particle with the dipole which it induces, the 1/${\mathit{r}}^4$ term (and the 1/${\mathit{r}}^6$ term is replaced by a 1/${\mathit{r}}^7$ term). The coefficient of the 1/${\mathit{r}}^5$ term is an integral over ω of the virtual photons exchanged between the charged particle and the system, with the integrand a function of the dynamic polarizability α(ω) and β(ω)-β(0). We examine the possibility of determining β(ω)-β(0) in a manner independent of the scattering or Rydberg bound-state problems in which they arose. Two approaches will be used, the first based on a method of obtaining upper and lower bounds on β(0), suitably adapted to study β(ω) over the low-frequency domain; the limitations lie not in the bounding techniques but in the reliability of the input data, the sum rules. The second, more interesting approach will be to show the relationship between β(ω) and the Faraday effect, thereby using the Faraday effect to illuminate scattering and bound-state phenomena, and vice versa. © 1996 The American Physical Society.

A general formalism for the description of spin and angular momentum projection sensitive (e,2e) processes valid for all electron energies is proposed. Using the relativistic distorted-wave Born approximation, a reasonable description of a recent (e,2e) experiment with spin-polarized relativistic electrons [H.-Th. Prinz, K.-H. Besch, and W. Nakel, Phys. Rev. Lett. 74, 243 (1995)] is obtained. A detailed numerical study of spin-sensitive (e,2e) processes on inner-shell states of high-Z atoms is presented. © 1996 The American Physical Society.

A high-resolution ultraviolet spectrometer was employed for a measurement of the H Lyman-β (H ${\mathrm{L}}_{\mathrm{\beta }}$) emission Doppler line profile at 1025.7 Å from dissociative excitation of ${\mathrm{H}}_2$ by electron impact. Analysis of the deconvolved line profile reveals the existence of a narrow central peak, less than 30 mÅ full width at half maximum (FWHM), and a broad pedestal base about 260 mÅ FWHM. Analysis of the red wing of the line profile is complicated by a group of Werner and Lyman rotational lines 160–220 mÅ from the line center. Analysis of the blue wing of the line profile gives the kinetic-energy distribution. There are two main kinetic-energy components to the H(3p) distribution: (1) a slow distribution with a peak value near 0 eV from singly excited states, and (2) a fast distribution with a peak contribution near 7 eV from doubly excited states. Using two different techniques, the absolute cross section of H ${\mathrm{L}}_{\mathrm{\beta }}$ is found to be 3.2±0.8×${10}^{\mathrm{-}19}$ ${\mathrm{cm}}^2$ at 100-eV electron impact energy. The experimental cross-section and line-profile results can be compared to previous studies of Hα (6563.7 Å) for principal quantum number n=3 and ${\mathrm{L}}_{\mathrm{\alpha }}$ (1215.7 Å) for n=2. © 1996 The American Physical Society.

Angular distribution of the ${\mathit{L}}_{\mathit{l}}$ x-ray line (3${\mathit{s}}_{1/2}$→2${\mathit{p}}_{3/2}$) in Au and Bi induced by 3–9 MeV carbon ions has been measured. Values of the alignment parameter (${\mathit{A}}_2$) of the ${\mathit{L}}_3$(2${\mathit{p}}_{3/2}$) subshell have been obtained from the data as a function of the carbon ion energy. The data have been compared with the calculations of the standard perturbed-stationary-state (PSS) theory with energy-loss (E), Coulomb deflection (C), and relativistic (R) corrections (ECPSSR) and ECPSSR with the intrashell (IS) effect included as a multiplicative factor. From this comparison it is evident that an account for the IS coupling substantially improves agreement between theory and measurement. The effect of simultaneous multiple ionization of the M and higher shells on the measured ${\mathit{A}}_2$ values is discussed. © 1996 The American Physical Society.

In this work a symmetric representation of the three-body Coulomb continuum wave function is constructed that represents an exact asymptotic solution of the many-body Schrödinger equation on a five-dimensional hypersphere of large hyperradius. Consequently, the wave function is shown to satisfy the Kato cusp conditions at all three two-body collision points. At finite distances the proposed solution is designed to account for properties of the total potential surface. In particular, dynamical stabilization due to the presence of ridge structure in the total potential (Wannier ridge) is encompassed in the present treatment. The behavior of the wave function at the total dissociation threshold is investigated. In order to allow for three-body interactions we linearly expand each two-body Coulomb potential in terms of all three two-body potentials. The expansion coefficients determine the amount of distortion of each two-body subsystem by the presence of the third particle and thus give direct information on the strength of three-body interactions. © 1996 The American Physical Society.

We present measurements and calculations of Δn=0 dielectronic recombination resonances of boronlike argon between 0.2 and 6 eV. A storage ring equipped with an electron cooler was used for the measurements. Methods employed to reduce the electron energy distribution and improve the accuracy of resonance energy measurements have yielded an energy resolution of 30 meV full width at half maximum at low energies, and an energy uncertainty better than 30 meV. The high energy resolution results from the use of an adiabatic expansion technique to reduce the transverse electron energy distribution. The improved accuracy in energy determinations is achieved through the inclusion of variations in the ion velocity, which occur during scans of the electron velocity, in the relative velocity transformations. Calculations of the resonance strengths and energies were made using two different methods, multiconfiguration Dirac-Fock and multiconfiguration Breit-Pauli approximations. A comparison of the experimental data to the calculations shows fair agreement in both the spectral features and integrated intensities above 3 eV. However, poor agreement is found below 3 eV. © 1996 The American Physical Society.

We report on the projectile energy dependence of the cross sections for producing the configurations 2${\mathit{lnl}}^{\prime }$ (n≥3) by double-electron capture in ${\mathrm{C}}^{6+}$+He collisions. The present measurements and calculations, which extend previous work performed on the 90-keV ${\mathrm{C}}^{6+}$+He system, give evidence for dynamic electron-correlation effects in double-capture mechanisms. A significant dependence on the collision energy is found for the cross sections associated with the configurations 2${\mathit{lnl}}^{\prime }$ (n≥5). Moreover, anisotropies of the angular distributions of Auger electrons originating from the configurations 2l3${\mathit{l}}^{\prime }$ are observed at 48 and 132 keV. The capture cross sections for producing some of the terms 2l3${\mathit{l}}^{\prime }$ ${}_{}{}^1{}_{}{}^{}$L are shown to depend on the collision energy. The cross sections for production of the magnetic substates ${\mathit{M}}_{\mathit{L}}$=0 associated with the configurations 2l3${\mathit{l}}^{\prime }$ are found to be the same for both energies of 48 and 132 keV. © 1996 The American Physical Society.

We study electron emission cross sections of He decaying to ${\mathrm{He}}^{+}$(1s) in the N=2 and 3 manifolds produced by fast proton and antiproton impact. Ab initio close-coupling calculations are carried out using the impact-parameter method. The electronic state during collision is expanded in terms of He wave functions obtained by the hyperspherical close-coupling method. The theory reproduces experimental findings regarding both the background and doubly excited resonances well. The resonance shapes are found to depend sensitively on the sign of the projectile charge. This is due to interference between the partial waves of the ejected electron. We analyze excitation paths that eventually lead to another interference effect between continuum and doubly excited states. We demonstrate importance of both the bound and continuum states as intermediate states. © 1996 The American Physical Society.

The Coulomb-Born approximation (CBA) is tested against experiment and against the distorted-wave Born approximation (DWBA) for target inner-shell ionization by fast electrons. It is found that the CBA is fairly accurate in the binary region for the heavy systems when relativistic effects play a minor role. However, CBA underestimates the cross sections in the recoil region for the heavy targets, but also in the binary region for light targets. This is caused by an inappropriate representation of the electronic wave functions, and is neither a deficiency of a first-order theory nor due to lack of orthogonality in the present form of the CBA. © 1996 The American Physical Society.