A dense atomic Rb beam, excited by three cw lasers to the 10${\mathit{F}}_{7/2}$ state, is found to contain substantial population in the 11${\mathit{D}}_{5/2}$ state, which lies 75 ${\mathrm{cm}}^{\mathrm{-}1}$ lower in energy. The mechanism for the population transfer is determined to be maser oscillation at the 10F-11D transition frequency, self-sustaining even in the absence of mirrors, which saturates the populations of the two levels. Although the maser radiation is not observed, the population levels and threshold conform to a simple rate equation model.

We have calculated the time evolution of the density matrix reduced to the spin degree of freedom for a particle in a spherical harmonic oscillator with a constant spin-orbit interaction. We have studied two classes of spatial wave functions in the initial state: pure orbital states ‖lm〉 and coherent states. When the initial spin is a pure state, its evolution in time produces a mixed state during a time called the collapse time. This behavior of the spin is similar to that observed in the Jaynes-Cummings model. A similar dynamics is produced for a broad range of geometrical initial conditions for the spin as well as for the wave packet. The system is exactly recurrent but we have also found the existence of approximate recurrences corresponding to a reversal of the spin direction. We have tentatively applied our result to mimic the evolution of the spin in the H atom. In this case only a few spin-orbit partners play a role and, after a long time, produce a state where the admixture is not complete. The average quantum behavior is always very different from that of a classical particle having a spin as a vector of constant length. The increase of the number 2S+1 of spin-orbit partners changes the time scale of the collapse by the factor √S , and a strong mixing is always observed.

Using a transit-time technique, the phase difference is calculated for a neutron traversing an interferometer accelerating in flat space-time. The result differs from that calculated in a gravitational setting by an amount five orders of magnitude smaller than that resolvable by current experiment. However, when identical slabs of matter are inserted into separate arms of an accelerating Mach-Zehnder interferometer a phase shift is calculated that is only two orders of magnitude smaller than that currently resolvable. This effect does not depend on dispersion in the material. Verification of this prediction, although beyond the resolution of current experiments, may be possible.

We construct potentials ${\mathit{V}}^{\mathrm{\{}\mathit{s}\mathit{c}\mathit{r}\mathit{K}\mathrm{\}}}$(r) which support a finite number scrK of bound states in such a way that the highest normalizable excitation lies precisely at the threshold energy E=0. We expect that many realistic interactions ${\mathit{V}}_{\mathrm{}\left(\mathrm{phys}\right)\mathrm{}}$(r) may be bracketed between these forces due to their flexibility and plausible screened Coulombic form. Thus, we propose an estimate of the number ${\mathit{N}}_{\mathrm{BS}}$ of bound states in an arbitrary potential ${\mathit{V}}_{\mathrm{}\left(\mathrm{phys}\right)\mathrm{}}$(r) via requirements ${\mathit{V}}^{\mathrm{\{}{\mathcal{K}}_{\mathit{L}}\mathrm{\}}}$<${\mathit{V}}_{\mathrm{}\left(\mathrm{phys}\right)\mathrm{}}$≥${\mathit{V}}^{\mathrm{\{}{\mathcal{K}}_{\mathit{U}}\mathrm{\}}}$ and subsequent inequalities ${\mathcal{K}}_{\mathit{L}}$≳${\mathit{N}}_{\mathrm{BS}}$≥${\mathcal{K}}_{\mathit{U}}$. In particular, we get a strict prediction ${\mathit{N}}_{\mathrm{BS}}$=${\mathcal{K}}_{\mathit{U}}$ whenever the bracketing proves tight enough, with ${\mathcal{K}}_{\mathit{U}}$≡${\mathcal{K}}_{\mathit{L}}$-1.

We discuss the fate of initial states of the Schrödinger cat type for the damped harmonic oscillator, mostly employing a linear version of the stochastic Schrödinger equation. We also comment on how such cat states might be prepared and on the relation of single realizations of the noise to single runs of experiments.

Using the beam-foil excitation method we have measured lifetimes for the 3p ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2,3/2}$ levels in Na-like Nb (${\mathrm{Nb}}^{30+}$). The decay curves were corrected for cascades using the rigorous arbitrarily normalized decay curve method. The lifetime values obtained, τ=70±5 and 29±2 ps for the 3p ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2}$ and 3p ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{3/2}$ levels, respectively, are in very good agreement with recent theoretical calculations.

Multielectron excitations in x-ray absorption of xenon in the energy region of the L edges are studied. Broad structures in the subshell absorption spectra are attributed to virtual collective excitations such as core relaxation and dielectric polarization. Three groups of sharp spectral features, corresponding to multielectron transitions involving 5p, 5s, and 4d electrons, respectively, are found. Due to the large lifetime width and multiplet spread, the features are superpositions of individual transitions within a group. From comparison of corresponding features in the three L-subshell spectra, some conclusions on the role of the inner-shell vacancy in the process can be drawn. Differences in ${\mathit{L}}_1$ and ${\mathit{L}}_{2,3}$ spectral features generally point to a complex excitation mechanism, although some cases seem to obey the simple sudden approximation. Evidence for a strongly coupled outer-shell excitation involving the 4d subshell is found.

The applicability and accuracy of the hyperspherical-coordinate method for the study of reduced-dimensional models of two-electron atoms and ions is discussed. We have calculated excitation spectra and ground-state wave functions and compared them with their exact values, and with the values obtained within different modifications of the Hartree-Fock approach.

We describe the N-electron atomic wave functions within the hyperspherical-coordinate framework. The wave functions, being solutions of the Schrödinger equation, are made to adapt the permutation symmetry of the symmetric group ${\mathit{S}}_{\mathit{N}}$. The effects of permutations on the wave functions are deduced, and the matrix elements of the atomic potential are presented.

In this paper we will address the question of how to obtain energies from functionals when only the functional derivative is given. It is shown that one can obtain explicit expressions for the exchange-correlation energy from approximate exchange-correlation potentials using line integrals along paths within the space of densities. The path dependence of the results is discussed and criteria for path independence are given. Derivations are given of upper and lower bounds to the exchange-correlation energy in terms of the exchange-correlation potential at the beginning and the end point of a certain path. We further express the kinetic part ${\mathit{T}}_{\mathrm{xc}}$ of the exchange-correlation energy in terms of a line integral and derive a constraint on approximate correlation potentials. We show how to use the line-integral formalism to derive the requirements that exchange-correlation potentials must fulfill in order to make the exchange-correlation functional satisfy some symmetry property such as rotational and translational invariance and scaling properties. Finally, we will discuss the use of line integrals along a path in density space to obtain energy differences, notably, the bonding energies of molecules, from exchange-correlation potentials. These last results generalize the transition-state formulations of Slater and Ziegler.

The results of beam-foil measurements of lifetimes for low-lying singlet levels in Mg-like chlorine, Cl vi, are presented. The decay curves were analyzed by means of the arbitrarily normalized decay curve method, combined with the recently developed canyl code, which facilitates studies of decay chains. Cascade corrected data are presented for the levels 3s3p ${}_{}{}^1{}_{}{}^{}$P, 3${\mathit{p}}^2$ ${}_{}{}^1{}_{}{}^{}$S, 3${\mathit{p}}^2$ ${}_{}{}^1{}_{}{}^{}$D, and 3s3d ${}_{}{}^1{}_{}{}^{}$D, whereas less rigorous lifetime values, based on curve fits, were obtained for the 3p3d ${}_{}{}^1{}_{}{}^{}$D, 3p3d ${}_{}{}^1{}_{}{}^{}$F, and 3s4f ${}_{}{}^1{}_{}{}^{}$F levels. The data are in excellent agreement with recent theoretical values, and previous discrepancies between experiment and theory for short-lived states have been removed.

In this paper, unified relativistic formulations with thermal effects of the Thomas-Fermi model for an atom within and without a very strong magnetic field are considered. The general formulations are then used to discuss the combined relativistic and thermal effects on some atomic properties.

We present the l- and n-mixing regions of the barium spectrum obtained in σ polarization in a magnetic field of 2.89 T using one-step atomic-beam uv laser spectroscopy. Unexpected differences between the ${\mathrm{\sigma }}^{+}$ and ${\mathrm{\sigma }}^{\mathrm{-}}$ spectra as well as extra structure are observed. An explanation in terms of the many-electron nature of the barium atom is proposed.

The ground states, as well as the 6s and 4f ionized states of Ba, Cs, and lanthanide atoms from La to Lu, are calculated with the nonrelativistic numerical Hartree-Fock (HF) method and an analytical HF method with Gaussian-type functions (GTF’s). It is shown that the nonrelativistic HF calculations well reproduce the experimental trends on the 6s and 4f electron ionizations, although the calculated 6s ionization potentials (IP’s) are smaller and the calculated 4f IP’s are larger than those given by experiment. The relativistic HF calculations with GTF’s are also performed on some selected atoms. The 6s IP’s given by the relativistic HF method are closer to experiment than those given by the nonrelativistic HF methods. The relativistic corrections make 4f IP’s smaller than those of experiment. Since the correlation effects increase the IP’s obtained by the HF calculations, the inclusion of the relativistic effects is indispensable in discussing IP’s quantitatively.

We have computed to high accuracy the energies and the total widths of five triply excited n=2 intrashell resonances in ${\mathrm{He}}^{\mathrm{-}}$, the 2${\mathit{s}}^2$2p ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$, 2s2${\mathit{p}}^2$ ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}^{\mathit{e}}$, ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}^{\mathit{e}}$, ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}^{\mathit{e}}$, and 2${\mathit{p}}^3$ ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}^{\mathit{o}}$. These states are characterized by strong localized and asymptotic correlation effects and by their proximity to He doubly excited states. The possible many open channels correspond not only to one- but also to two-electron continua. The resonance parameters were established by applying the complex-coordinate rotation method with large basis sets of orbital and ${\mathit{r}}_{\mathit{i}\mathit{j}}$-correlated configurations. The expansion length of the trial wave functions went up to 1300 terms for the 2s2${\mathit{p}}^2$ ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}^{\mathit{e}}$ resonance. This resonance is found to be below the He 2s2p ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$ threshold, in agreement with experimental observations and contrary to existing theoretical results. Similarly, the position of the 2s2${\mathit{p}}^2$ ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}^{\mathit{e}}$ resonance is also below the He 2${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}^{\mathit{e}}$ threshold, in agreement with a recent theoretical prediction. The widths of these states range from 10 meV for the 2s2${\mathit{p}}^2$ ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}^{\mathit{e}}$ to 331 meV for 2${\mathit{p}}^3$ ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}^{\mathit{o}}$.

The absorption oscillator strength of the xenon 147-nm resonance transition is measured to be 0.264±0.016. This value is from direct absorption measurements with equivalent widths from ≊1 to ≊10 ${\mathrm{cm}}^{\mathrm{-}1}$. This f-value measurement is compared to others in the literature and is used in Monte Carlo simulations of trapped decay rates. The simulations include an angle-dependent partial frequency redistribution. The simulation results are compared to trapped decay rates in the literature.

We present high-resolution (${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$) and high signal-to-noise ratio (2000) infrared line shapes of CO perturbed by Xe, ${\mathrm{N}}_2$, and He in the intermediate regime from Doppler to collision broadening. It is found that the pressure-broadened component of the line shape cannot be fit by a Lorentzian line shape, and the largest deviation occurs in the core of the line. A speed-dependent collisional width is required to fit the spectra broadened by the larger Xe perturber, for which the collision rate of a CO molecule is determined primarily by its own speed. A line-shape model based on the theory of Robert et al. [Phys. Rev. A 47, R771 (1993)], folding in the effect of Dicke narrowing, is derived. The speed-dependent mechanism also appears to explain the measurements made by Duggan et al. [Phys. Rev. A 48, 2077 (1993)] in a dilute CO:${\mathrm{N}}_2$ mixture, in which a non-Lorentzian collision broadening scheme was suggested.

The relativistic Fock-space coupled-cluster method for the direct calculation of ionization potentials and excitation energies (including fine structure) is applied to the 4${\mathit{f}}^2$ levels of ${\mathrm{Pr}}^{+3\mathrm{}}$ and the 5${\mathit{f}}^2$ levels of ${\mathrm{U}}^{+4\mathrm{}}$. The no-pair Dirac-Coulomb-Breit Hamiltonian is taken as the starting point. Correlation is treated by the coupled-cluster singles-and-doubles approximation, which includes single and double virtual excitations in a self-consistent manner, incorporating therefore the effects of the Coulomb and Breit interactions to all orders in these excitations. Extensive basis sets of kinetically balanced four-component Gaussian spinors are used to span the atomic orbitals. All levels appear in correct order. The average error of the excitation energies with the best basis is 222 ${\mathrm{cm}}^{\mathrm{-}1}$ for ${\mathrm{Pr}}^{+3\mathrm{}}$ and 114 ${\mathrm{cm}}^{\mathrm{-}1}$ for ${\mathrm{U}}^{+4\mathrm{}}$. Fine-structure splittings are obtained with even better accuracy.

The specific mass shift in the electron affinity between ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$ and ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ has been determined by tunable-laser photodetachment spectroscopy to be -0.51(14) GHz. The isotope shift was observed as a difference in the onset of the photodetachment process for the two isotopes. In addition, the electron affinity of Cl was found to be 29 138.59(22) ${\mathrm{cm}}^{\mathrm{-}1}$, giving a factor of 2 improvement in the accuracy over earlier measurements. Many-body calculations including lowest-order correlation effects demonstrate the sensitivity of the specific mass shift and show that the inclusion of higher-order correlation effects would be necessary for a quantitative description.

Calculations of vibrational energies and rotational constants are carried out for the van der Waals trimer ${\mathrm{Ar}}_2$-HF. The calculations include all five intermolecular degrees of freedom. The different intramolecular vibrational states v of the HF molecule are separated out adiabatically, so that the calculations are carried out on effective intermolecular potentials for each HF vibrational state separately. Calculations are performed both on pairwise-additive potentials, derived from the well-known Ar-Ar and Ar-HF potentials, and on nonadditive potentials, incorporating various different contributions to the three-body forces. The results are compared with experimental results from high-resolution spectroscopy, and provide detailed information on the anisotropy of the nonadditive intermolecular forces. As in previous work on ${\mathrm{Ar}}_2$-HCl, it is found that a very important nonadditive term arises from the interaction between the permanent multipoles of the HF molecule and the exchange quadrupole caused by distortion of the two Ar atoms as they overlap. An improved model of this term is described.