Fully relativistic, ab initio calculations of the rate of dielectronic recombination (DR) have been performed for fluorinelike ${\mathrm{Mo}}^{33+}$ to magnesiumlike ${\mathrm{Mo}}^{30+}$ and chlorinelike ${\mathrm{Mo}}^{25+}$ and argonlike ${\mathrm{Mo}}^{24+}$. Calculations of the rate of excitation autoionization (EA) have been performed for neonlike ${\mathrm{Mo}}^{32+}$ to aluminumlike ${\mathrm{Mo}}^{29+}$ and argonlike ${\mathrm{Mo}}^{24+}$ and potassiumlike ${\mathrm{Mo}}^{23+}$. The detailed calculations of the atomic structure and rate coefficients for charge states in these groups allow interpolation of the DR and EA rates for the more complex ions having 3${\mathit{s}}^2$3${\mathit{p}}^{\mathit{k}}$ (k=1–4 for DR and k=2–5 for EA) ground states. The calculations for DR are broken up by different classes of excitation channels; simple, analytic formulas are then fit to the calculations. The effects of configuration interaction on the rates of DR and EA have been studied in detail and are found to have a slight effect on only a small class of the Auger rates needed for the present work. Radiative transitions between energy levels in the continuum are investigated and found to have a moderate effect on the DR rates and a small effect on the EA rates of the ions in this paper. © 1996 The American Physical Society.

In the classical model for Rydberg atoms, the transition from a pure Zeeman effect to a pure Stark effect passes through a teardrop bifurcation when the magnetic quantum number is not zero. © 1996 The American Physical Society.

Relativistic configuration interaction hyperfine constants (HFC) have been obtained for all 5${\mathit{p}}^5$(5d+6s+6p) ${}_{}{}^{133}{}_{}{}^{}\mathrm{I}$ levels. The 22 magnetic dipole constants, A, agree with experiment to 12% or better for all but three levels. Many of the odd J=1,2 levels, which include these three, exhibit large many body effects. Our values for the quadrupole HFS constants are considerably smaller than the few highly uncertain experimental values, which we believe need remeasurement. There are also significant many body results present in the lowest ${}_{}{}^{137}{}_{}{}^{}\mathrm{I}$ odd parity J=1,2 levels; here, there are no experimental results available. We have found certain excitations from the 4d subshell to be important; we ascribe this to the presence of an open 5p subshell. © 1996 The American Physical Society.

A theoretical approach is developed to describe the effect of the anisotropy of the intermolecular potential on the far wings of the profile of collision-induced rotational spectra for a linear-molecule–inert-gas atom system. A calculation is made for a simple model system, and collisional propagation is found to have a significant role in determining the profile. © 1996 The American Physical Society.

A Kohn-Sham formalism for the treatment of excited states within the density-functional theory (DFT) is presented. DFT exchange and correlation energy functionals for excited states are defined. Explicit expressions for these functionals are derived by generalizing a recent DFT perturbation theory. A computational scheme for the treatment of excited states within the DFT is suggested. Differences of Kohn-Sham eigenvalues are shown to be well-defined approximations for excitation energies. Correction terms to these approximations are presented. Perturbation theory expansions for band gaps are discussed. © 1996 The American Physical Society.

An alternative form of the variational principle is set up by defining an action functional which takes explicit account of the time path and thus is different from that used traditionally in time-dependent density-functional theory. This has the attractive feature of not having the formal difficulties in defining the effective potential and the effective interaction as its functional derivatives. Also, the Berry phase, not explicitly found at first sight in a time-dependent density-functional theory, is shown to reside in this action functional. It lies buried as the sum over the individual phases of the occupied states associated with the time-dependent Kohn-Sham orbitals. Some recent work on superconductivity and ferroelectricity in the literature are cited as examples of the Berry-phase considerations developed here. © 1996 The American Physical Society.

Rotational perturbations in the B${\mathrm{}}^3$${\mathrm{\Sigma }}_{\mathit{u}}^{\mathrm{-}}$ state of molecular oxygen are studied by measuring high-resolution vacuum ultraviolet laser photoabsorption cross sections of the (16,0)–(18,0) B${\mathrm{}}^3$${\mathrm{\Sigma }}_{\mathit{u}}^{\mathrm{-}}$←X${\mathrm{}}^3$${\mathrm{\Sigma }}_{\mathit{g}}^{\mathrm{-}}$ Schumann-Runge bands of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}_2^{}{}_{}{}^{}$. The observation of numerous extra lines in the spectrum, together with ab initio calculations of relevant potential-energy curves, enables the perturbing state to be assigned as the second valence state of ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$ symmetry. This weakly bound state, which we name ${\mathit{C}}^{\prime 3}$${\mathrm{\Pi }}_{\mathit{u}}$, is also likely to be principally responsible for the well-known rapid increase in the magnitudes of the B-state triplet-splitting constants ${\lambda }_{\mathit{v}}$ and ${\gamma }_{\mathit{v}}$ as the dissociation limit is approached. © 1996 The American Physical Society.

We have investigated the accuracy of the local-spin-density approximation with orbital-density-dependent self-interaction correction (LSDSIC) as proposed by Perdew and Zunger within a Kohn-Sham approach in which electrons with a given spin projection all move in a single optimized effective potential (OEP). We have also studied the accuracy of the Krieger-Li-Iafrate (KLI) approximation to the OEP for the same energy functional in order to assess its applicability to systems in which the integral equation for the OEP cannot be reduced to a one-dimensional problem, e.g., molecules. Self-consistent Kohn-Sham LSDSIC calculations have been performed for atoms with atomic number Z=1–20 in the exchange-only case for the total energy, the highest-occupied orbital energy ${\mathrm{\epsilon }}_{\mathit{m}}$, and the expectation value of ${\mathit{r}}^2$. In addition, the structure of the resulting exchange potential is examined and compared with the exact exchange-only density-functional theory (OEP method with Hartree-Fock exchange-energy functional) results. Furthermore, we display ${\mathrm{\epsilon }}_{\mathit{m}}$, the ionization potential I, and the electron affinity A when both exchange and correlation energy effects are included. Finally, we also consider the results of evaluating the LSDSIC energy functional by employing the exact (in the central-field approximation) single particle orbitals as proposed by Harrison. We find that the LSDSIC energy functional generally leads to calculated values that are superior to those provided by the LSD approximation and that the KLI approximation yields results in excellent agreement with the corresponding exact OEP results for this energy functional. In particular, quantities strongly related to the behavior of the valence electrons are nearly identical in both the OEP and KLI calculations, i.e., the difference between the 〈${\mathit{r}}^2$〉 and ${\mathrm{\epsilon }}_{\mathit{m}}$ is less than 0.2% on average, while the difference between the calculated I is less than 0.2 millihartree on average with the corresponding difference of only 0.1 millihartree for A. © 1996 The American Physical Society.

An ab initio method for high accuracy calculations for atoms with more than one valence electron is described. The effective Hamiltonian for the valence electrons is formed using many-body perturbation theory for the interaction of the valence electrons with the core. The configuration-interaction method is then used to find the energy levels of the atom. An application of this to thallium shows that the method gives an accuracy of about 0.5% for the ionization potential and a few tenths of a percent for the first few energy intervals. © 1996 The American Physical Society.

The character of Raman dispersion is investigated for radiative and nonradiative resonant x-ray scattering of systems with vibrational degrees of freedom. It is shown that the center of gravity of the resonantly scattered x-rays and electrons of such systems is strongly dependent on frequency and spectral shape of the incoming x-ray radiation and on the parameters defining the potential surfaces of the states involved in the scattering event. Contrary to nonresonant x-ray and Auger emission, narrow band resonant excitation leads to a strong nonlinear dependence of the center of gravity, with an asymmetrical frequency dependence for this quantity. Contrary to atomic systems it is shown that resonant x-ray scattering of molecules often is guided by an anti-Raman dispersion law. © 1996 The American Physical Society.

The wavelengths of the 1${\mathit{s}}^{21}$${\mathit{S}}_0$–1${\mathit{snp}}^1$${\mathit{P}}_1$ (n=6–12) transitions in He-like Al XII have been measured in laser-produced and X pinch plasmas. The accuracy of the present measurements (0.3–0.5 mÅ) is a severalfold improvement over previous results. In addition, the resonance transitions from the ${11}^1$${\mathit{P}}_1$ and ${12}^1$${\mathit{P}}_1$ levels of He-like Al XII are observed. Finally, the Rydberg series is used to determine the ground-state ionization energy of Al XII, with a precision of 50 parts per million. This method gives ${\mathit{E}}_{\mathrm{ion}}$=2085.98±0.10 eV. These experimental results are compared with theoretical data calculated by several different methods. © 1996 The American Physical Society.

Electron-impact ionization of the 3${\mathrm{\sigma }}_{\mathit{g}}$ and 1${\mathrm{\pi }}_{\mathit{u}}$ molecular orbitals of ${\mathrm{N}}_2$ to produce the ${\mathit{X}}^{\mathrm{}2}$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$ and ${\mathit{A}}^{\mathrm{}2}$${\mathrm{\Pi }}_{\mathit{u}}$ states of ${\mathrm{N}}_2^{\mathrm{}+}$ has been investigated in an asymmetric (e,2e) experiment at the 100-eV maximum of the total ionization cross section. The experiment allows the direct comparison of ionization of two molecular orbitals in the same target molecule. Scattering angles of the incident electron <5° and ejected electron energies from 3 to 13 eV were used. The relative triple differential cross sections were obtained as a function of ejected electron angle for both the binary (parallel to momentum transfer direction) and recoil (antiparallel) directions. The maxima of the binary and recoil peaks were found to be shifted from the angular positions predicted by first-order theory. In contrast to the typical atomic case, the recoil peaks were shifted to smaller ejection angles. In addition, the binary peak of the 1${\mathrm{\pi }}_{\mathit{u}}$ orbital ionization was located at an angle 30° larger than the corresponding peak for the 3${\mathrm{\sigma }}_{\mathit{g}}$ orbital. These results suggest that the experiment is very sensitive to the initial and final states of the target. Differences from results with atomic targets may be related to the nonspherically symmetric nature of the target and residual ion. © 1996 The American Physical Society.

The Dirac R-matrix theory is used to calculate the collision strengths for electron scattering from boronlike iron in the energy range 0–300 Ry. The target model space encompasses 15 fine-structure levels, and all 105 Δn=0 transitions together with 40 partial waves are included in the calculation. The results are compared with previous semirelativistic R-matrix calculations where the relativistic effects are taken into account via some term coupling effects and also with the relativistic distorted wave, which take relativistic effects adequately but do not include effects due to the resonances. We also compare our results with recent Breit-Pauli R-matrix calculations where available. We find that there are some important differences between these different calculations. The need to work within a fully relativistic scheme including the resonance effects is stressed. © 1996 The American Physical Society.

We study the role of electron correlation during a high-energy ion-atom collision (dynamic correlation). We show how to define a reference calculation in which correlation is not included during the collision whereas it is included in the initial and final states (frozen-correlation approximation). Correlation may be characterized by a typical time ${\mathit{t}}_{\mathrm{corr}}$. The frozen-correlation approximation corresponds to the form of the transition amplitude when assuming that ${\mathit{t}}_{\mathrm{corr}}$ is much larger than the collision time. We apply our theory to double excitation and single ionization of helium and show that dynamic correlation may play a more important role in ionization than in double excitation. © 1996 The American Physical Society.

The method of electron-photon coincidence is used to ‘‘resolve’’ the electron-impact excitation of the n${\mathrm{}}^1$P levels (n=3 and 4) from nearby levels. Experimentally determined ratios of the differential cross sections for the electron-impact excitation of 1${\mathrm{}}^1$S→2${\mathrm{}}^1$P, to 1${\mathrm{}}^1$S→3${\mathrm{}}^1$P, and 4${\mathrm{}}^1$P transitions are presented at 30-, 40-, and 80-eV incident electron energies. Differential cross sections for the 1${\mathrm{}}^1$S→3${\mathrm{}}^1$P and 1${\mathrm{}}^1$S→4${\mathrm{}}^1$P transitions are derived by normalizing these ratios to available experimental differential cross sections for the 1${\mathrm{}}^1$S→2${\mathrm{}}^1$P transition. The ratios and differential cross sections are compared to available theoretical and semiempirical data. © 1996 The American Physical Society.

Small-angle ${\mathrm{H}}^0$+${\mathrm{H}}_2$ and ${\mathrm{H}}^0$+${\mathrm{O}}_2$ collisions are studied at energies of 1.0, 2.0, and 3.0 keV. Time-of-flight techniques are used to identify the dominant direct scattering (→${\mathrm{H}}^0$) processes. The stripping (→${\mathrm{H}}^{+}$) and electron capture (→${\mathrm{H}}^{\mathrm{-}}$) channels are identified by electrostatic energy analysis. The probabilities and reduced differential cross sections for the dominant processes are determined as a function of τ (=Eθ), the reduced scattering angle. This is found to be a useful variable for plotting the probabilities and reduced cross sections for the processes studied, since the results at the different energies generally lie on common curves. The electronically inelastic processes are found to dominate the collision for τ>0.2 keV deg in H+${\mathrm{H}}_2$ and τ>0.3 keV deg in H+${\mathrm{O}}_2$. The stripping process in ${\mathrm{H}}_2$ primarily results in ${\mathrm{H}}^{+}$+${\mathrm{H}}_2$(X)+${\mathit{e}}^{\mathrm{-}}$ while the ${\mathrm{H}}^{+}$+${\mathrm{O}}_2^{\mathrm{-}}$ channel is found to dominate the small-angle stripping in ${\mathrm{O}}_2$. © 1996 The American Physical Society.

The response of an arbitrary scattering problem to quasistatic perturbations in the scattering potential is naturally expressed in terms of a set of local partial densities of states and a set of sensitivities each associated with one element of the scattering matrix. We define the local partial densities of states and the sensitivities in terms of functional derivatives of the scattering matrix and discuss their relation to the Green’s function. Certain combinations of the local partial densities of states represent the injectivity of a scattering channel into the system and the emissivity into a scattering channel. It is shown that the injectivities and emissivities are simply related to the absolute square of the scattering wave function. We discuss also the connection of the partial densities of states and the sensitivities to characteristic times. We apply these concepts to a δ barrier and to the local Larmor clock. © 1996 The American Physical Society.

The cross section as well as the branching ratios for the dissociative recombination of ground-state ${\mathrm{CH}}^{+}$ ions with electrons have been measured using the heavy-ion storage-ring technique and two-dimensional fragment imaging. Although the absolute value of the cross section at thermal energies is found to be in very good agreement with the theory, several unpredicted narrow resonances are also present in the data. These structures are interpreted as due to an indirect recombination process via core-excited Rydberg states. The branching-ratio measurement shows that at low electron energy the 2${\mathrm{}}^2$Π state, producing carbon fragments C${(}^1$D), is the most important dissociative state, although transitions during the dissociation to other dissociative potential curves are also present. Anisotropy in the angular distribution of the dissociating fragments is visible for some of the final states. Dissociative recombination of ions in the metastable excited a${\mathrm{}}^3$Π state is also observed, and the lifetime as well as the excitation energy of this state are deduced from the imaging data. © 1996 The American Physical Society.

State-selective single electron capture, in collisions of multicharged ions ${\mathrm{Kr}}^{8+}$ at 18 keV with laser-excited Rydberg ${\mathrm{Rb}}^{\mathrm{*}}$(${\mathit{n}}_{\mathit{ip}}$) atoms, is investigated by use of a field ionizing lens system (FILS), in a three-crossed-beam experiment. By scanning the laser over a wide range of wavelengths (303–298 nm), this investigation covers the 15p–25p Rydberg series, showing the influence of the initial state of Rb. For every well-defined ${\mathrm{Rb}}^{\mathrm{*}}$(${\mathit{n}}_{\mathit{ip}}$) state, (i) very high Rydberg states of the ${\mathrm{Kr}}^{7+\mathrm{*}}$(n) product ions are detected as a consequence of the high degree of excitation of the target and of the high charge of the projectile, and (ii) the n distribution of the capture cross section is obtained in the domain 67≤n≤95, by measuring the energy spectrum of the ${\mathrm{Kr}}^{8+}$ ions produced by field ionization in the FILS of the excited product ions ${\mathrm{Kr}}^{7+\mathrm{*}}$. These n distributions become wider and are systematically shifted towards higher n values as ${\mathit{n}}_{\mathit{i}}$ increases. By using the classical trajectory Monte Carlo method, the n distributions are calculated for the ${\mathit{n}}_{\mathit{ip}}$ series. Although the calculated n distributions are systematically wider, the behavior of their widths and of their relative positions is in agreement with the experiment. On the other hand, the extended classical over-the-barrier model yields n distributions significantly narrower than the experimental ones. © 1996 The American Physical Society.

Yield spectra of multiply charged ions have been measured in coincidence with threshold electrons near the Xe ${\mathit{L}}_3$-shell ionization region. The ion-yield spectra exhibit characteristic profiles of postcollision interaction effects induced by Auger cascades following Xe ${\mathit{L}}_3$-shell ionization. The peak shifts of the spectral profiles increase gradually along with the increase of the charge states, but the peak widths are almost independent of the charge states. The spectral profiles are reproduced by a simple model based on the assumption that Coster-Kronig and Auger shake-off decays play a major role in the Auger cascades following the Xe ${\mathit{L}}_3$-shell vacancy creation. © 1996 The American Physical Society.