It is argued that our (ZP92) local exchange-correlation functional [Phys. Rev. A 46, R5320 (1992)] gives superior results for the total energies of ${\mathrm{H}}_2$ and ${\mathrm{N}}_2$ as functions of internuclear distance.

The Auger resonant Raman effect provides a unique method to eliminate the lifetime broadening in resonant Auger spectra. The method is now used to resolve experimentally the fine structure of the Xe 4${\mathit{d}}_{5/2}^{\mathrm{-}1}$6p→5${\mathit{p}}^{\mathrm{-}2}$6p transitions. The strength of the electron correlation effects has been studied by comparing the observed intensity distribution with multiconfiguration Dirac-Fock predictions.

A quantal description of classically unstable motion which employs the intergration of the Schrödinger equation along a path in the complex-coordinate plane is described. It is shown that a region in the complex-coordinate plane exists where the Schrödinger wave function is well described in a harmonic-oscillator approximation. The breakup of the hydrogen molecule ion ${\mathrm{H}}_2^{+}$ is used as a prototype to illustrate the method.

Ab initio calculations show that a curve crossing is not always needed for a high dissociative-recombination cross section. For ${\mathrm{HeH}}^{+}$, in which no neutral states cross the ion potential curve, dissociative recombination is driven by the nuclear kinetic-energy operator on adiabatic potential curves. The kinetic-energy derivative operator allows for capture into repulsive curves that are outside of the classical turning points for the nuclear motion. The dominant dissociative route is the ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ state leading to H(n=2) atoms. An analogous mechanism is proposed for the dissociative recombination of ${\mathrm{H}}_3^{+}$.

Double and single ionization of He by proton (p) and antiproton (p¯) impact in the energy region below 50 keV is studied theoretically within a molecular picture. As the energy decreases, the ratio of the double- to single-ionization cross section is found to increase for p¯ impact and to decrease to p impact in agreement with recent measurements. For p impact, the dominant mechanism for double ionization at the lower energies seems to be sequential ladder climbing by the two electrons through various excited channels. For p¯ impact, in contrast, the approaching negative charge distorts the He electron cloud toward the other side of the nucleus and decreases the electron binding energies. These effects enhance the important role of electron-electron, interactions, increasing double ionization.

We study the role of atomic collisions in future measurements of an intrinsic electric-dipole moment (EDM) of the electron using laser-cooled Cs atoms in an optical trap or in an atomic fountain. We find that the shift in frequency and the line broadening caused by collisions may eventually limit the achievable sensitivity of these EDM experiments. We present the results of a coupled-channel calculation of these quantities and discuss the symmetry aspects and magnetic-field dependences.

The semiclassical approximation of Feynman’s path integral is used to calculate the S matrix for the positron-impact ionization of hydrogen. The formulation provides a full scattering amplitude, and more importantly does not require knowledge of the asymptotic three-body Coulomb state in the continuum. In the limit of vanishing excess energy, the results confirm Wannier’s classical model for fragmentation [Phys. Rev. 90, 817 (1953)]. The experimentally observable ratio of fragmentation versus total ionization (including positronium formation) is predicted.

Absolute integral cross sections for low-energy scattering of neutral sodium clusters ${\mathrm{Na}}_{\mathit{n}}$ (2<n<20) by ${\mathrm{C}}_{60}$ fullerenes have been measured. Cluster-cluster interaction is dominated by long-range van der Waals forces. Interaction constants determined from the data are in good agreement with the prediction of dispersion theory based on the spectral properties. The large cluster polarizabilities are responsible for the high strength of the interaction potential and, consequently, for the large center-of-mass cross sections (≳5000 A${\mathrm{̊}}^2$ for ${\mathrm{Na}}_{20\mathrm{-}}$${\mathrm{C}}_{60}$ collisions).

Calculations on the steady-state distribution of atoms cooled in three coplanar laser beams are presented. For this three-beam configuration, the achievements of Sisyphus cooling are independent of fluctuations in the relative time phases between the beams. The atomic motion is quantized and the steady-state solution of the density-matrix equations is found within a secular approximation. We obtain a minimum width of the cooled momentum distributions on the order of six photon momenta.

We report steady-state gain due to coherence effects in a potassium-helium mixture, for strong pumping near the ${\mathit{D}}_2$ line and probing near the ${\mathit{D}}_1$ line. The absorption-gain spectra are in good agreement with a four-level Raman-driven, lasing with inversion model, where collisional transfer populates the probed excited state. Using parameters corresponding to the experimental conditions, the model predicts gain without bare-state population inversion by a large margin.

Technical aspects of a recently constructed strong version of Bell’s theorem are discussed. The theorem assumes neither hidden variables nor factorization, and neither determinism nor counterfactual definiteness. It deals directly with logical connections. Hence its relationship with modal logic needs to be described. It is shown that the proof can be embedded in an orthodox modal logic, and hence its compatibility with modal logic assured, but that this embedding weakens the theorem by introducing as added assumptions the conventionalities of the particular modal logic that is adopted. This weakening is avoided in the recent proof by using directly the set-theoretic conditions entailed by the locality assumption.

Lowest-order perturbative calculations of the electron-positron production probability in relativistic heavy-ion collisions exceed unitarity bounds for the heaviest collision systems at extreme relativistic energies and sufficiently small impact parameters. Starting with the exponential representation of the time-evolution operator in the Furry picture, we derive manifestly unitary and gauge-invariant expressions for transition amplitudes and probabilities associated with the created electron-positron pairs by employing the Magnus expansion to first order. The time-evolved ground state of the electron-positron field around the heavy nuclei is expressed as a superposition of the unperturbed vacuum state and virtual excitation modes consisting of electron-positron pairs.

A striking spectral-modulation effect has been observed by means of a proper postselection procedure under conditions where the spatial shift of the wave trains greatly exceeds the coherence length of the neutron beams traversing an interferometer. It is shown that Schrödinger-cat-like states are created by the superposition of two coherent states generated in the interferometer. These entangled states exhibit, under certain circumstances, characteristic squeezing phenomena, indicating a highly nonclassical behavior. Analogies with optical experiments are discussed.

We measured the branching ratio R of ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$→4γ with respect to ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$→2γ as [1.48±0.13(statistical)±0.12(systemic)]×${10}^{\mathrm{-}6}$. The upper limits of the branching ratios for the exotic particles are obtained to be around 3×${10}^{\mathrm{-}7}$.