Atomic ${\mathit{g}}_{\mathit{j}}$ factors have been calculated for Li, ${\mathrm{Be}}^{+}$, and ${\mathrm{Ba}}^{+}$ with accurate relativistic wave functions obtained in the coupled-cluster single- and double-excitation approximation. Correlation due to the Coulomb as well as the Breit interaction is included. The results are -2.002 301 58(20), -2.002 262 77(50), and -2.002 491 1(30) for Li, ${\mathrm{Be}}^{+}$, and ${\mathrm{Ba}}^{+}$, respectively, which agree well with the experimental results -2.002 301 00(64), -2.002 262 36(33), and -2.002 490 6(12). The inclusion of the Breit interaction in the wave functions gives significant contributions to the final results.

The commutation-anticommutation relations of q-electron operators imply a set of N representability conditions [A. J. Coleman, Rev. Mod. Phys. 31, 668 (1963)] for the corresponding q-order reduced density matrices (q-RDM) [C. Valdemoro, An. Fis. 79, 95 (1983); in Structure, Interaction and Reactivity, edited by S. Fraga (Elsevier, Amsterdam, 1992)]. From these conditions, a general and closed-form relation is obtained here. In this equation the part involving RDM’s has the same structure as that involving hole reduced density matrices. This relation is the basis of a method for approximating a q-RDM in terms of the r-RDM’s [C. Valdemoro, Phys. Rev. A 45, 4462 (1992)] with r<q. The derivation of this relation can be simplified significantly by employing a graph method which is described here. These graphs are in a one-to-one correspondence with the elements of the symmetric group of permutations.

The general equation linking a q-order reduced density matrix (q-RDM) with the corresponding q-order hole reduced density matrix (q-HRDM) has been reported in the preceding paper [F. Colmenero, C. Perez del Valle, and C. Valdemoro, preceding paper, Phys. Rev. A 47, 971 (1993)]. In this equation, neither Kronecker δ functions nor mixed products of elements of RDM’s and HRDM’s appear, and the part involving hole terms has the same structure as that involving particle terms. Recently [C. Valdemoro, Phys. Rev. A 45, 4462 (1992)], a similar equation for q=2 has been used to approximate the 2-RDM from the knowledge of the 1-RDM. Here, the 3-RDM and the 4-RDM are approximated by using the 2-RDM as an initial datum. The ultimate aim of this research is to develop an iterative method for solving the contracted form of the Schrödinger equation [L. Cohen and C. Frishberg, Phys. Rev. A 13, 927 (1976); H. Nakatsuji, ibid. 14, 41 (1976)]. A matrix form in the orbital representation of this equation is reported here. Finally, the second-order hypervirial equation, also in its matrix form, has been derived so that the quality of the results can be judged.

Excited neutral triatomic hydrogen and deuterium molecules formed by electron-impact excitation have been investigated. We report on the autoionization of ${\mathrm{H}}_3^{\mathrm{*}}$ and ${\mathrm{D}}_3^{\mathrm{*}}$ molecules produced by the reactions ${\mathrm{H}}_2^{+}$+${\mathrm{H}}_2$→${\mathrm{H}}_3^{\mathrm{*}}$+${\mathrm{H}}^{+}$ and ${\mathrm{D}}_2^{+}$+${\mathrm{D}}_2$→${\mathit{D}}_3^{\mathrm{*}}$+${\mathrm{D}}^{+}$. We measured the lifetime of ${\mathrm{H}}_3^{\mathrm{*}}$ and ${\mathrm{D}}_3^{\mathrm{*}}$ and the branching ratio between ${\mathrm{H}}_3^{\mathrm{*}}$, ${\mathrm{D}}_3^{\mathrm{*}}$, and ${\mathrm{H}}_3^{+}$, ${\mathrm{D}}_3^{+}$ production channels.

A method based on the modified Faddeev equations in the total-angular-momentum representation is developed to treat the zero-energy scattering in symmetric three-body Coulomb systems. The method is applied to calculate the s-wave scattering lengths of the systems ${\mathit{e}}^{\mathrm{-}}$+(${\mathit{e}}^{\mathrm{-}}$${\mathit{e}}^{+}$), p+(pμ), and d+(dμ). A large negative value of the even-parity p+(pμ) scattering length indicates the presence of a virtual state near threshold.

We report measurements of the angular distribution of positronium formed by charge exchange of monoenergetic positrons in molecular hydrogen for various incident positron energies. These data are compared with recent calculations of Ps formation in ${\mathrm{H}}_2$. The implications of these results for the formation and potential utility of energetic positronium beams are discussed.

An analysis is made of the background level and counter efficiencies actually necessary to perform a loophole-free Einstein-Podolsky-Rosen experiment. Both requirements are correlated. Photon counters do not absolutely have to have more than 82.8% efficiency if the signal-over-noise ratio is very high.

We discuss the possibility of searching for correlation of nuclear spin with the momentum of a photon I⋅k, which is due to parity nonconservation. The manifestation of this effect is a dependence of the nuclear magnetic resonance frequency on the direction of the laser beam. Theoretically the effect can reach a value of ∼${10}^{\mathrm{-}15}$ eV and even larger. For realistic conditions it is smaller, but still it is larger than the sensitivity achieved in experiments on searching for parity and time invariance violation in atoms.

We present K Auger spectra arising from collisions of ${\mathrm{N}}^{6+}$ ions with a Ni(110) target for different kinetic energies and observation angles. The bulk of the electrons is ascribed to emission below the surface. At very low collision velocities (${\mathit{v}}_{\mathrm{\perp }}$≤${10}^{\mathrm{-}2}$ a.u.) we find a pronounced contribution from electrons emitted prior to impact. The velocity dependence of the above-surface component is used for the experimental determination of the time scales involved in electron emission above the surface. Comparison with theoretical estimates is also presented.

We have observed the K-shell Auger spectrum in atomic oxygen. A total of ten transitions originating from the decay of the ${}_{}{}^4{}_{}{}^{}$P and ${}_{}{}^2{}_{}{}^{}$P states of the ${\mathrm{O}}^{+}$(1${\mathit{s}}^{\mathrm{-}1}$) ion are identified and assigned to final states of the ${\mathrm{O}}^{2+}$ ion. Relative intensities for each of these transitions are obtained, allowing the extraction of the dependence of the Auger decay on the multiplet structure in both the initial and final states of this basic open-shell atom.

A previous experimental study of Ar L-vacancy production in slow ${\mathrm{Ar}}^{+}$+${\mathrm{SiH}}_4$ collisions is reanalyzed to provide evidence for the dielectronic process of (inverse) autoexcitation, which removes an electron from a deep inner shell by interaction with another electron decaying from an upper level. Analytic models are evaluated to treat alternative cases where two electrons are transferred at a curve crossing and between parallel potential curves. The theoretical results confirm the experimental observation that the Ar L-vacancy production increases with decreasing energy.

The decay of valence satellite states in neon above the first double-ionization threshold has been studied experimentally and theoretically. Special emphasis was given to differentiate between two decay modes: valence Auger and valence-multiplet Auger decay. It is shown that the latter process is predominant in the low kinetic energy part of the spectrum. The main structures of this low-energy Auger spectrum could be designated by help of calculated transition energies and decay rates.

High-resolution inverse Raman experiments for ${\mathrm{H}}_2$ dilute in Ar [R. L. Farrow et al., Phys. Rev. Lett. 63, 746 (1989)] have revealed remarkable deviations from the usual linear mixing rule for the Q-line broadening. They have been interpreted using a line-profile model that takes into account the spectral narrowing induced by speed-changing collisions. The present approach includes the role of collisions changing both speed and phase, leading to an alternative interpretation of the above-noted experiments. This interpretation generalizes the earlier study and points out the various mechanisms of line formation.

We describe local and nonlocal Gaussian orbital-spin-polarized density-functional calculations for clusters of two to seven niobium atoms. The most stable geometries found with geometry optimization have a high atomic coordination. The trends in the experimental binding energies, bond dissociation energies, and ionization potentials are well reproduced with the exception of the pentamer bond dissociation energy, which is too low. The possible causes are discussed. These are the most extensive state-of-the-art calculations to date for the clusters of a transition metal.

A detailed classical analysis of the interaction of an atomic electron with an oscillating electric field with arbitrary initial quantum state n, magnetic quantum number m>0, field strength, and frequency shows that the classical dynamics for the perturbed electron can be stabilized for large fields or high frequencies. Using a map approximation to the classical dynamics, explicit formulas are derived for the full parameter dependence of the boundaries of stability surrounding the domain of rapid classical ionization. These results provide motivation and guidance for further theoretical and experimental studies of the stabilization of atoms in superintense microwave and laser fields.

We investigate microwave excitation of helium 28 ${}_{}{}^3{}_{}{}^{}$S Rydberg atoms and find that a second microwave field lifts the degeneracy of certain Floquet states describing the 28 ${}_{}{}^3{}_{}{}^{}$S He atom plus single microwave field system. As a result a microwave pulse produces two patterns of Stueckelberg oscillations. They depend sensitively on the frequencies and amplitudes of both microwave fields and are influenced differently by added noise. We present two-frequency Floquet maps showing the origin of the interferences.

We report the results of analytical and numerical investigations on the ionization of a classical atom in a strong, linearly polarized, monochromatic field. We show that the ionization probability decreases with increasing field intensity at field amplitudes much larger than the classical chaos border. This effect should be observable in real laboratory experiments.

We establish nonlinear coupling instabilities in an optical open-flow system. The coupling considered in this Hamiltonian system arises from the optical Kerr effect and exists among beams that belong to different mode families in optical guided configurations such as multimode fibers. The amplitude and power of each of the beams are found to be spatially unstable and chaotic for four-beam coupling and spatially oscillatory for two-beam interaction dependent on launch conditions.

Within the modified Riccati approach developed elsewhere, we construct quasiexactly solvable potentials related to the Pöschl-Teller and modified Pöschl-Teller potentials. This is achieved by considering closed-form wave functions whose logarithmic derivatives are rational in the mapping u(x)=cosh(x) or u(x)=cos(x). With the hyperbolic mapping we construct an interesting four-parameter quasiexactly solvable confining potential with one, two, or three minima upon the value of its coupling constants. We give explicit expressions for the bound-state eigenfunctions and corresponding energy levels for some particular cases. The analytic continuation x→ix transforms the previous potential into a periodic confining well, or a Kronig-Penney-like potential with an interesting structure of minima in each cell and a finite number of gaps. The energy levels in the last case are some of the band edges of the spectrum. In any case a finite but arbitrarily large number of energy levels and corresponding eigenfunctions are determined from the diagonalization of a finite matrix.

In this paper we generalize Wang’s approach [J. Phys. A 20, 5041 (1987)] and investigate the algebraic structure of the Schrödinger equation associated with a general driven time-dependent oscillator. Using the Lie-algebraic technique we obtain an exact form of the time-evolution operator which, in turn, enables us to derive the propagator of the system readily. Since the propagator is for the most general time-dependent oscillator, results for any special case can be easily deduced from it. These results will be useful for future studies in quantum optics as well as in atomic and molecular physics.