Large-basis-set multireference singly and doubly excited configuration-interaction calculations give electron affinities (EA’s) 0.278, 1.264, 1.454, and 3.363 eV for atoms B, C, O, and F, in excellent agreement with observed values 0.28, 1.268, 1.462, and 3.399 eV. The study relies on systematic expansion of reference space and curves of energy versus weight of reference configurations to obtain EA’s within 0.01 eV of the full configuration-interaction limit for the chosen basis.

We use Floquet theory, fully resolved numerical simulation, and laboratory experiment to study two quasiperiodic modes in the Couette-Taylor system which have the same symmetry but different spatial structure. Although each mode has been observed in previous experiments, their coexistence in the same region of parameter space is a new numerical prediction. Because they have the same symmetry, the modes are strongly coupled, which results in chaotic behavior.

I describe experiments on ‘‘pulses’’ of convective traveling waves in an ethanol water mixture contained in an extremely uniform annular cell. In contrast to previous observations, I find that pulses drift continuously, with no long-term change in velocity. The drift velocity vanishes at onset, increases with the distance above onset, and agrees with the results of numerical integrations of the Navier-Stokes equations.

We develop a general model for flow suspended particles in a porous medium. The model can take into account the effects of the morphology of the porous medium (including pore surface roughness and fractality), the chemistry of the flowing fluid, and all important forces between the particles and the pore surface. If surface deposition and pore plugging by size exclusion take place, the process is a percolation phenomenon which may belong to a different universality class than that of random percolation. The model is applied to two classes of problems, flow of solid, electrically charged colloidal particles, and that of stable emulsion droplets in a porous medium.

It is proposed that the anomalous loading observed in tokamak ion-Bernstein-wave (IBW) experiments is due to a class of sheath-plasma waves (SPW) which propagate on high-voltage rf sheaths near the antenna. Particle simulations in one and two dimensions confirm the existence and scalings of the SPW. Coupling to the SPW modes can dominate coupling to the IBW, and qualitatively yields the observed dependences of antenna loading on parallel wave number, plasma density, and magnetic field. Antennas which minimize rf sheaths should improve the effectiveness of IBW heating.

We report on the atomic dynamics of a simulated Lennard-Jones liquid confined in a plane micropore when the density profile approximates to two dense slabs with a low-density region between. The atomic motion parallel to the slit is essentially diffusional. The atomic motion across the slit comprises statistically independent, very fast, but infrequent, jumps of atoms from one slab to the other, a novel observation in this field. These atomic dynamical events accurately obey Poisson statistics but are consistent with the static density profile in the gap. This system is proposed as a model classical (as opposed to quantum mechanical) microscopic physical system which obeys Poisson statistics.

Grazing incidence x-ray diffraction has been used to characterize the near surface structure of an aromatic polyimide film. It is shown that within the first 90 Å from the surface the ordering of the polymer molecules is markedly enhanced. As the penetration depth of the x rays decreases, reflections characteristic of density correlations along the polymer chain axis shift to smaller scattering vectors and those indicative of intermolecular ordering become clearly evident. Thus, near the surface essentially crystalline order is seen.

We present small-angle neutron-scattering measurements of the static structure factor S(q) of the binary fluid mixture water-lutidine imbibed into the porous glass Vycor as a function of temperature and composition. S(q) changes from a Lorentzian in the one-phase region to a Lorentzian squared at the random-field transition. We relate the correlation lengths (9 Å≲ξ≲52 Å) to the previously measured relaxation times and find finite-size and random-field effects.

We have obtained images of individual Xe atoms adsorbed on a Ni(110) surface using a low-temperature scanning tunneling microscope (STM). The atom-on-jellium model has been used to calculate the apparent height of a Xe atom as imaged with the STM and the result is found to be in good agreement with experiment. We conclude that the Xe 6s resonance, although lying close to the vacuum level, is the origin of the Fermi-level local state density which renders Xe ‘‘visible’’ in the STM.

We have investigated the effect of the saturation of surface dangling bonds of Si(111) surfaces with atomic hydrogen upon Ag thin-film growth. By using time-of-flight-type low-energy ion scattering-recoil analysis techniques, we find that the growth mode of Ag thin films is drastically changed by the hydrogen termination of Si(111)-7×7 surfaces and that the epitaxial growth of A-type Ag(111) films is promoted by the hydrogen atoms residing at the film/substrate interface.

Equations of motion for the nonlinear optical response of arbitrary-size molecular aggregates are derived. The relative role of intramolecular and intermolecular (two-exciton) nonlinearities and the cooperative enhancement induced by the latter are analyzed. A crossover from ∼${\mathit{N}}^2$ to ∼N scaling of the nonlinear polarizability is predicted as the aggregate dimension becomes comparable to the optical wavelength, N being the aggregate size. The limitations of the local-field approximation are demonstrated.

We demonstrate that the optical second-harmonic (SH) efficiency of a clean metal surface is strongly influenced by the presence of monatomic steps. Vicinal Al surfaces, oriented between 0 and ±10° of the (100) plane, were prepared in vacuum; the SH light was produced by picosecond laser pulses with 570<λ<820 nm incident at angles up to 67.5°. From the dependence of the SH signal on angle of incidence, wavelength, surface orientation, and oxygen exposure, we conclude that the macroscopic SH polarization of the vicinal Al surface contains comparable contributions from the (100) terraces and the surface steps.

We have demonstrated that laser vaporization of nonmetallic solids can produce atomic or molecular clusters and cluster ions by direct ejection of fragments from the sample surface. The spectra of cluster ions ([MX${]}_{\mathit{n}}$${\mathit{M}}^{+}$ and [MX${]}_{\mathit{n}}$${\mathit{X}}^{\mathrm{-}}$, n=1–40) formed by vaporizing mixed alkali-halide powder samples include virtually no alloyed species, indicating that the observed clusters do not grow from molecular vapor but are instead laser sputtered from the solid in a nonthermal shattering process. In carbon, large clusters result from partial evaporation of ultrafine particles on the sample.

General arguments are presented which tend to show that adatom-substrate bonds are likely to exhibit negative-U behavior. This is confirmed by a direct calculation for Au and GaAs(110). It is shown that a natural consequence of this is the pairing of adatoms as observed in scanning-tunneling-microscopy experiments. The distance in energy between the two ionization levels of the pair is correctly predicted as well as the sign of the tunnel current.

Femtosecond spectroscopic measurements of optically induced magnetization are performed on new type-II ZnTe/${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se diluted-magnetic-semiconductor heterostructures consisting of magnetic quantum wells confined by nonmagnetic barrier layers. The formation and evolution of electron-based bound magnetic polarons in the wells is observed through static and time-domain experiments. Energy-dependent magnetic spin dynamics on ultrashort time scales are seen to vary dramatically with the degree of electronic confinement.

Frictional drag between isolated two-dimensional electron gases separated by a thin barrier has been observed at low temperatures in GaAs/AlGaAs double-quantum-well structures. Separate electrical connection to the two electron systems allows the injection of current into one and the detection of a small drag voltage across the other. The drag voltage is a direct measure of the interwell momentum relaxation rate. Measurements of this rate are in qualitative agreement with calculations of an interwell Coulomb scattering model.

The collective excitations of the fractional-quantum-Hall liquid are studied within the Ginzburg-Landau theory. We show that (1) Gaussian fluctuations of the phase of the order parameter correspond to the cyclotron mode with an energy gap of ħ${\mathrm{\omega }}_{\mathit{c}}$ at q=0 and a contribution to the static structure factor proportional to ‖q${\mathrm{\Vert }}^2$ as q→0, in accordance with Kohn’s theorem, and (2) vortex-antivortex fluctuations give rise to the lowest-Landau-level collective mode with an energy gap that depends only on the Coulomb energy and a static structure factor that vanishes as ‖q${\mathrm{\Vert }}^4$ as q→0.

The quasistatic spin-freezing temperature ${\mathit{T}}_{\mathit{f}}$ of thin layers of CuMn and AgMn remains nonzero down to thicknesses ${\mathit{W}}_{\mathrm{SG}}$ of 1 and 2 monolayers, respectively. These alloys thus remain spin glasses at such layer thicknesses, in agreement with published evidence of similar behavior for a two-dimensional, short-range, insulating spin glass. For ${\mathit{W}}_{\mathrm{SG}}$≤5 monolayers, we find ${\mathit{T}}_{\mathit{f}}$∝${\mathit{W}}_{\mathrm{SG}}^{\mathit{a}}$ as predicted by Fisher and Huse, with an exponent a=0.8±0.1.

A cluster-model analysis is made on the material dependence of the optical charge-transfer gap and antiferromagnetic superexchange interaction of a variety of insulating cuprates. It is shown that the electronic structure of cuprates typically of the charge-transfer type is characterized by the unique energy-level separation that reflects the three dimensionality of the crystal via the long-range Madelung potential; such characteristics are absent in the Mott-Hubbard regime.

We have performed variational Monte Carlo calculations for the two-dimensional t’-J model (t’ is an effective, describe fermionic holes hopping in a background liquid of singlet bonds represented by products of bosonic spin operators. The variational energies we obtain from these wave functions can be directly compared with those of other proposed wave functions. We find that our energies are lowest in the t’/J≪1 limit.