It has been shown recently that one can construct a local relativistic quantum field theory which admits small violations of the Pauli exclusion principle by introducing ‘‘paronic’’ states which obey para-Fermi statistics of order 2. Paronic shifts are calculated for the low-lying states of helium to aid in the design of experiments either to detect paronic helium, or place upper limits on its possible existence.

A nonadiabatic variational procedure is used to diagonalize the Hamiltonian of the helium atom to obtain the ${}_{}{}^3{}_{}{}^{}\mathrm{S}_{}^{\mathrm{e}}{}_{}{}^{}$ states. A partial-wave analysis of the wave functions has been made. The one-body densities and the shape densities have been investigated. Detailed information on electron-electron correlation has been obtained. The K-classification scheme has been recovered. The strong radial-angular correlation regions together with the associated twin nodes have been discovered.

A hybrid of the Coulomb-projected Born and distorted-wave Born methods has been applied to electron-impact excitation of the hydrogen atom and the results have been compared with other theoretical and experimental results.

A two-potential localized exchange approach is used to study the coherence and alignment in electron-lithium resonant (2s-2p) excitation processes at intermediate electron energies of 10, 15, and 20 eV. Furthermore, the total and differential spin asymmetry in the resonant scattering of spin-polarized electrons with spin-polarized lithium atoms is also investigated.

Within a virial expansion of the electrical conductivity of a fully ionized plasma, which takes into account many-particle effects, different limiting cases are considered. An appropriate interpolation formula is compared with experimental values.

Markovian time evolutions with nonincreasing entropy were investigated by Hu [Phys. Rev. A 34, 596 (1986)]. After reformulating what Hu called the I theorem (in contrast to Boltzmann’s H theorem), we analyze the structure of such time evolutions.

The initial sticking in the $2p_m$ states of muonic helium in muon-catalyzed fusion ($\mu \mathrm{CF}$) and the subsequent collisional excitation to these states are shown to have nonstatistical dependences on $m$ that result in spatial anisotropy of the emitted x rays. This anisotropy, $\frac{I\left(0\mathrm{}°\right)}{I\left(90\mathrm{}°\right)}$, is found to be 0.71 for $d-d$ $\mu \mathrm{CF}$ and 1.12 for $d-t$ $\mu \mathrm{CF}$ in liquid targets, where the angle is between the coincidently detected x ray and neutron. The effect is predicted to increase the actual $K\alpha$ x-ray yield and corresponding sticking observed in a recent $d-t$ $\mu \mathrm{CF}$ experiment by 4%. The Doppler broadening of the radiation observed at different angles is also examined.

We report on the observation of spatiotemporal chaos in a multimode continuous ${\mathrm{Na}}_2$ ring laser optically pumped by a single-mode ${\mathrm{Ar}}^{+}$ laser. Measurements of the intensity of the emitted beam at two different points of the beam cross section reveal different temporal behavior of those two signals. Power spectra, fractal dimensions, and correlations indicate that both signals are chaotic and are generated by a common attractor.

We calculate the line shift in the three-photon resonance-absorption experiment performed by Ferrel, Payne, and Garrett [Phys. Rev. A 36, 81 (1988)] and find it large, to the violet, and close to experiment. In comparison, the calculated single-photon resonance shift in absorption is a factor of 30 times smaller and to the red. The three-photon resonance shift depends on the relative propagation directions of the excitation beams, and we present a formula for the case where only two excitation beams are present.

We measured the relative cross section and angular distribution parameter for 5s photoelectron emission in atomic cadmium across the region of the 4d→nl autoionizing resonances between 11.70 and 18.05 eV. Our results for the oscillator strengths agree with Hartree-Fock calculations, and are higher than the values reported by other experiments. Strong departure from the direct-process value of 2.0 was observed for the angular distribution parameter β, indicating singlet-to-triplet mixing in the wave functions. The mixing varies in the np resonance series, while it remains almost constant throughout the nf series. In the region of the 5p resonances there is good agreement with a semiempirical calculation of the asymmetry parameter. A number of double-electron excitations were investigated and the value of β was used to give the correct assignment to a transition at 12.856 eV. A previously unobserved transition corresponding to the promotion of a 4d electron to the 5d orbit was detected by the change in the value of β.

Energy values for the ground and three lowest excited singlet S states of helium have been calculated using hyperspherical coordinates in a variational basis consisting of Sturmian functions in R, Legendre polynomials in ${\theta }_{12}$, and problem-optimized functions in α. No adiabatic hypothesis is made. The convergence and energy values are superior to previous calculations using similar methods, but not as good as calculations in which $r_{12}$ is explicitly included. Plots of (H-E)Φ(R,α,${\theta }_{12}$) versus R and α are presented, and they show that the greatest departure from zero is in the α≊0 region.

Ion trapping and spin-dependent charge-exchange techniques were used to determine the electron g factor of ${\mathrm{H}}_2^{+}$ as a first step to provide a precise test of the theory of molecular g factors. Accessible to us were the vibrational states 4, 5, and 6. Averaged over these vibrational states we obtain g(v=4,5,6) =2.002 2837(18) 7(18) in agreement with the corresponding theoretical value of g=2.002 282 8(8). As a by-product we have measured the rotational g factor to be $g_{\mathrm{rot}=0.920\mathrm{}\left(40\right)\mathrm{}}$, compared with the calculated value of $g_{\mathrm{rot}=0.9244\mathrm{}}$.

We report the observation of the 5g-4f Rydberg-Rydberg infrared transition of nitric oxide at 2500 ${\mathrm{cm}}^{\mathrm{-}1}$ using high-resolution (0.03 ${\mathrm{cm}}^{\mathrm{-}1}$) Fourier-transform spectrometry. A rotationally cold (70 K) and resolved spectrum has been obtained in emission from a supersonic jet discharge. A spectrum emanating from hot (850-K) NO gas has also been observed. This spectrum exhibits characteristic spikes reflecting the quantization of the electron angular momentum along the axis of fast core rotation. Both spectra are quantitatively reproduced by theory. The manifestation of ‘‘circular’’ states in the hot spectrum is discussed.

A new approach for the calculation of ground states of many-electron systems is proposed via an integral formulation of the Hohenberg-Kohn-Sham density-functional theory. Only equations for the total electron density are involved; orbitals are not employed. Exchange and correlation effects are incorporated. In place of the set of single-electron equations, the total electron density is explicitly expressed in terms of the Kohn-Sham effective local potential through multidimensional integrations. The development is based on the first-order density matrix as obtained from the one-body Green’s function in polygonal and Fourier path-integral representations. This might open up the possibility of ab initio calculations for molecules with very many electrons. It also provides explicit solutions to two long-standing problems: electron kinetic energy and momentum density as functionals of the total electron density. The formulation can also be used in calculations for general fermions.

A new approach for the calculation of thermal properties of many-electron systems is proposed via an integral formulation of the Mermin-Kohn-Sham finite-temperature density-functional theory. The electron density of a thermal-equilibrium state can be determined by solving self-consistently equations for the electron density without using orbitals. Exchange and correlation effects are incorporated. In place of the set of the single-electron equations, the total electron density is explicitly expressed in terms of the Kohn-Sham effective local potential through multidimensional integrations. The development is based on the first-order density matrix as obtained from the one-body Green’s function in polygonal and Fourier path-integral representations. The formulation can also be applied to general fermions.

A new approach for the calculation of the linear response of both the ground and thermal-equilibrium states of many-electron systems is proposed via an integral formulation of the density-functional theory. Based on the path-integral representation of the one-particle Green’s function, the frequency-dependent linear-response function for the Kohn-Sham noninteracting system is expressed as an explicit functional of the Kohn-Sham local potential, instead of the summation over the single-electron orbitals. Thus the dynamic linear density response can be determined as the solution of self-consistent equations which only need as input the total electron density of the ground or the equilibrium state. Exchange and correlation effects are incorporated. Because orbitals are not employed, the formulation provides the possibility for calculations of linear-response properties, such as dynamic polarizability and photoabsorption cross sections of systems with very many electrons. The present formulation can also be applied to general fermions.

We analyze properties of the density matrix of doubly excited two-electron systems formed in inelastic collisions. Formulas for the two-particle joint angular probability density, the angular correlation function, and the reduced single-particle density are derived. Of particular interest is the interplay between the intrinsic correlations of the stationary two-electron state and collisionally induced coherences. We focus on its effects on the correlated and single-particle motion of the electrons. If one chooses approximate stationary wave functions reflecting the approximate O(4)×O(4)⊃O(4) dynamical symmetry, a simple quasiclassical interpretation of coherence and correlation in terms of shapes and modes of the relative motion of Kepler orbits can be given. The present description is applied to recent experimental results by Van der Straten and Morgenstern [Comments At. Mol. Phys. 19, 243 (1986)].

The drift velocity of electrons in Ar, Kr, and Xe has been measured at a gas temperature T=301 K using gas pressures of 300 and 600 kPa over the E/N range 2×${10}^{\mathrm{-}20}$≤E/N≤3×${10}^{\mathrm{-}17}$ V ${\mathrm{cm}}^2$. The measurements have been used to derive the low-energy momentum-transfer cross section ${\sigma }_m$(ɛ) in Kr and Xe at electron energies up to 8 eV using a Boltzmann-equation analysis along with a four-parameter modified-effective-range-theory procedure. Particular attention has been paid to the effects of impurities on the measured electron drift velocities and the uniqueness of the derived momentum-transfer cross sections. The present measurements and calculated cross sections are compared with published values from experiments and calculations.