The vibration-rotation spectrum of the helium molecular ion ${(}^3$He ${}_{}{}^4{}_{}{}^{}$He${)}^{+}$ has been observed for the first time. The Doppler-tuned ion-beam laser-resonance technique was used. Nine transitions in the fundamental band have been measured with an uncertainty of 0.0006 ${\mathrm{cm}}^{\mathrm{-}1}$ or 0.3 ppm. The accuracy exceeds that of the available theory by more than 3 orders of magnitude.

By use of the recently proposed model of the dynamics of a macromolecule in transient extensional flows, the effective viscosity increase in turbulence due to unraveling macromolecules is calculated, and a relation between this viscosity increase and a drag reduction parameter (the slope increment) is derived. The predictions of the theory are in good agreement with experiment.

A new set of integrable soliton equations describe caviton formation in a plasma. The equations are solvable by the inverse scattering transform. The time evolution of the scattering data is obtained and it is found that, unlike other integrable equations where the magnitude of the reflection coefficient was always a constant of the motion, here it may grow and/or decay in time. One physical manifestation of the growth of the reflection coefficient is the growth of density ripples in front of a microwave source. On the other hand, when the decay conditions dominate, one is left with only cavitons, which are the solitons for these equations.

An equation of motion is derived for the surface harmonic measure and the surface Green’s function in a class of diffusive growth processes, including diffusion-limited aggregation as a special case. These equations, in conjunction with a scaling hypothesis, imply a relation between the ‘‘multifractal’’ spectrum of exponents and the mass scaling of the clusters generated by these processes. Under some circumstances, this relation is inconsistent with a scaling law proposed by Turkevich and Scher.

We have directly observed chemisorption-induced changes in surface chemical bonding using a scanning tunneling microscope (STM). The dissociative adsorption of ${\mathrm{NH}}_3$ on Si(001) preserves the (2×1) local symmetry, but STM images reveal changes in the spatial distribution of occupied electronic states which allow us to distinguish reacted and unreacted Si(001) dimers. The STM results on the reacted surface are interpreted in terms of tunneling through localized Si-H bonding orbitals of a Si(001)-(2×1)H monohydride.

We present the results of a high-resolution x-ray scattering study of the thermal roughening of Ag(110). Using scattering from the bulk forbidden (11¯0) surface peak as a probe, we obtain direct information about thermal variations in the height-height correlation function. Specifically, we find that the surface undergoes a roughening transition at $T_R$=(450±25)°C. Above $T_R$, the rough phase is characterized by logarithmically divergent height fluctuations.

Using the high-Q mechanical-oscillator technique we have measured the sound velocity and mechanical dissipation of high-purity single-crystal silicon as functions of temperature (0.005–4.2 K), frequency (0.6–6.0 kHz), and strain amplitude (${10}^{\mathrm{-}5}$–${10}^{\mathrm{-}8}$). In the mechanical properties we find a surprisingly strong temperature dependence with the same qualitative behavior for silicon as for vitreous silica. This implies a density of two-level systems only 2 orders of magnitude lower for silicon than amorphous silica. In silicon we find evidence for a new dissipation mechanism at low temperatures and report the first observation of a saturation with strain of the resonant contribution to the sound velocity.

Concentrated suspensions of submicron colloidal spheres were studied both by dynamic light scattering and by direct observation of their phase behavior. In agreement with recent theory and computer simulation, the measured dynamic structure factor developed an essentially nondecaying component, implying ‘‘structural arrest,’’ at almost the same concentration as that at which a long-lived amorphous or glass phase was first observed.

The formation of acceptor-hydrogen complexes in silicon is studied via the electric field gradients caused by H atoms at the site of radioactive ${}_{}{}^{11}{}_{}{}^{}\mathrm{In}$ acceptor atoms, and is measured by means of the perturbed γγ angular correlation technique. The identical In-H pairs which are oriented along 〈111〉 lattice directions are found in samples hydrogenated by different methods, well known for the passivation of shallow acceptors. They dissociate around 420 K and are more stable than B-H complexes. There is evidence for an influence of the free-hole concentration on the actual structure of the In-H pairs.

We report a very careful, self-consistent, relativistic pseudopotential calculation of the interfacial dipole double-layer potential, valence-band offset, and formation enthalpy of (GaAs${)}_3$(AlAs${)}_3$(110). A comparison is made with identical calculations for the (001) superlattice with the following results [(001) in parentheses]: The interfacial dipole layer is 315 (154) meV. The formation enthalpy per twelve-atom unit cell is -21.9 (+1.7) meV. The valence-band offset is 447 (446) meV. This lends credence to the idea that the band offset is a difference of bulk quantities and that vastly different interfaces set up whatever double layer is necessary to maintain that difference.

We present evidence that the ground state of the frustrated Heisenberg antiferromagnet in two dimensions is well described by a fractional quantum Hall wave function for bosons. This is compatible with the resonating valence-bond concept of Anderson in being a liquid with neutral spin-(1/2 excitations. Our results suggest strongly that the resonating valence bond and fractional quantum Hall states are the same thing. We also argue that the excitation spectrum ahs an energy gap.

We study the spin polarization of secondary electrons from Fe(110) excited by noble-gas ions from 0.5 to 4 keV energy, covering the range potential emission to kinetic emission of secondary electrons. We find majority-spin polarization at all energies and for all ion species, but less than with primary electrons from the same sample. There is no magnetically ‘‘dead’’ layer produced, even by heavy sputtering. This leads to the possibility of ‘‘magnetic sputter depth profiling’’ which is demonstrated by sputter profiling through a 50-Å iron oxide layer on iron while the secondary-electron spin polarization is monitored.

When are molecular wires thin enough to show one-dimensional exciton kinetics? Cylindrical napthalene wires (5–5000 nm radius) show a definite one- to three-dimensional transition (about 25 nm for triplet excitons at 4 K; 40 nm at 77 K). Nuclepore channel-pore membranes (polycarbonate) serve as templates and calibrators. Vycor glass pores are effectively one dimensional. The triplet exciton migration (multiple hopping) length is 50–100 molecules. The recombination involves free and bound excitons.

Low-temperature photovoltaic spectra in ${\mathrm{Cu}}_2$O/Cu are attributed to the diffusion of n=1 excitons and their subsequent dissociation at the metal-semiconductor interface.

Quantum fluctuations of the proposed superconducting string with Bose charge carriers are studied in terms of the vortices on the string world sheet. In the thermodynamical limit, we find that they appear in the form of free vortices rather than as bound pairs. This fluctuation mode violates the topological conservation law on which superconductivity is based. However, this limit may not be reached. The critical size of the superconducting string is estimated as a function of the coupling constants involved.

Two-dimensional Poincareaa-invariant self-dual fields are consistently quantized. A fermionic formulation is shown to be equivalent to a nonlocal bosonic one. Self-dual boson fields are solitons describing a charge-density wave of paired fermions.

A very simple derivation of a closed-form solution to the stochastic evolution defined by Adler’s overrelaxation algorithm is given for free massive and massless scalar fields on a finite lattice with periodic boundary conditions and checkerboard updating. It is argued that the results are directly relevant when critical slowing down reflects the existence of Goldstone bosons in the system.

Using a hybrid molecular-dynamics simulation of lattice QCD we measure the spatial screening lengths of local meson and baryon operators with two flavors of Kogut-Susskind fermions. In the high-temperature phase the meson and nucleon screening lengths are parity doubled and their inverses are comparable to the zero-temperature masses. We construct chiral projections for the meson and nucleon propagators which demonstrate the chiral symmetry in a way independent of the extraction of masses from the propagators.

We have found a narrow line (intrinsic width ≤2.5 keV) at 1062±1 keV in the summed-energy 180°-c.m.-correlated two-photon spectrum from 5.95-MeV/nucleon U+Th collisions. Including possible systematic uncertainties, the production cross section is found to be 50±25 μb, averaged over the 1-mg/${\mathrm{cm}}^2$ Th target thickness. This line may belong to the decay of a neutral system which also produces correlated electron-positron pairs found by others in the same reaction.

Total reaction cross sections of neutron-rich nuclei from C to Mg in a thick Si target have been measured by the detection of the associated γ rays in a 4π geometry. This cross section strongly increases with neutron excess, indicating an increase of as much as 15% of the reduced strong absorption radius with respect to stable nuclei.