We have studied theoretically the spectrum of hydrogen atoms subjected to a certain class of perturbations, including the van der Waals and the diamagnetic interactions. We find a universal adiabatic invariant for this class. In special cases the system exhibits dynamical symmetry and an analytic spectrum. The pattern of energy levels in general can be understood in terms of the adjacent symmetries.

New variational techniques are described which yield a factor of 1000 improvement in accuracy for the energies of the 1snd ${}_{}{}^1{}_{}{}^{}\mathrm{D}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{D}$ states of helium up to n=8. Convergence to better than ±10 kHz is obtained, making possible high-precision comparisons with experiment for fine structure and singlet-triplet splittings. The comparisons are sensitive to QED, relativistic recoil, and second-order mass-polarization corrections.

A striking feature of recent measurements of the photoionization of ${\mathrm{H}}_2$(${\mathrm{C}}^1$${\mathrm{\Pi }}_{\mathrm{u}}$) is that the distribution of final vibrational states of ${\mathrm{H}}_2$${\mathrm{}}^{+}$ differs significantly from the predictions of the Franck-Condon approximation. A theory is presented that accounts for these measurements. The essential physical mechanism is photoexcitation of the dissociating, autoionizing ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }_{\mathrm{g}}^{}{}_{}{}^{}$ electronic state of ${\mathrm{H}}_2$, followed by competition between dissociation of the nuclei (leading to ${\mathrm{H}}^{\mathrm{*}}$+H) and electronic autoionization (leading to ${\mathrm{H}}_2$${\mathrm{}}^{+}$+e).

We give experimental spectra for 70- and 62-keV x rays inelastically scattered from the K-shell electrons of copper. The x rays scattered from the K shell were selected by fluorescence coincidence. The scattering is in a momentum-transfer regime in which the impulse approximation is not valid, and atomic binding effects are important. The data are in agreement within experimental uncertainties in absolute scattering strength and spectral shape with a Hartree-Fock-Slater calculation. In contrast to previous work we do not see separate spectral features attributable to Compton and Raman scattering.

The absolute field-ionization yields of gas- and foil-excited Rydberg states are measured for different fast beam ions. From the yields a direct comparison of the quantum-state populations of high-n states (n>100) produced by gas and foil excitation could be obtained. Model calculations are consistent with the high-n states being predominantly produced by excitation of the projectile or capture of target electrons in the last layers of the solid target.

Absolute cross sections for transfer ionization in ${\mathrm{H}}^{+}$+${\mathrm{H}}^{\mathrm{-}}$ collisions have been measured in the center-of-mass energy range 50 eV–40 keV, with the use of merged- and crossed-beam techniques, together with coincident detection of the products. A mechanism is proposed for the process in the low-energy region. The cross section, calculated accordingly, is found to be in satisfactory agreement with the experimental data.

A new approach for the calculation of ground states of many-electron systems is developed via an integral formulation of the Hohenberg-Kohn-Sham density-functional theory. Orbitals are not employed. In place of the set of one-electron equations, the total electron density is explicitly expressed in terms of the Kohn-Sham local potential through a multidimensional integration. This offers the possibility of ab initio calculations for molecules with very many electrons. The method can also be applied to calculate Compton profiles.

Unsteady fast dynamo action is obtained in a family of stretch-fold-shear maps applied to a spatially periodic magnetic field in three dimensions. Exponential growth of a mean field in the limit of vanishing diffusivity is demonstrated by a numerical method which alternates instantaneous deformations with molecular diffusion over a finite time interval. Analysis indicates that the dynamo is a coherent feature of the large scales, essentially independent of the cascade of structure to small scales.

Flow-visualization studies and heat-flux measurements during the early evolution of convection in a cylindrical container of aspect ratio 10 (radius/height) are reported. The heat current was ramped linearly, or modulated time periodically, from below to above the onset value. A novel sidewall design allowed pattern formation to occur independently of container geometry. In the earliest stages, the patterns were composed of irregularly arranged cells and varied randomly between experimental runs. The results demonstrate the importance of stochastic effects during the pattern evolution.

On the basis of theory and computer simulations we show that electrostatic turbulence in a cylindrical plasma with magnetic shear and curvature self-organizes to form a macroscopic potential φ which depends only on the radial coordinate r and is given by φ(r)≃${\mathrm{J}}_0$(pr)+${\mathrm{C}}_1$${\mathrm{r}}^2$+${\mathrm{C}}_2$ where ${\mathrm{C}}_1$ and ${\mathrm{C}}_2$ are functions of a constant p. A unique feature of the potential is the existence of a coaxial φ(${\mathrm{r}}_0$)=0 surface at ${\mathrm{r}}_0$≃0.7a, where a is the radius of the cylinder. This surface is found to be fairly rigid and is considered to inhibit radial particle transport.

By seeding of an ion wave by means of optical mixing, it was possible totally to suppress stimulated Raman scattering in a laser plasma. A counterpropagating seed beam with 1% of the intensity of the main beam was sufficient. A novel frequency– and wave-number–resolved image of the Thomson-scattered plasma-wave spectrum was used to shed light on the competition between stimulated Raman scattering and stimulated Brillouin scattering.

Ion-implantation–induced crystalline krypton inclusions in aluminum, epitaxially aligned with the matrix, have been investigated with x-ray diffraction and Rutherford-backscattering channeling analysis. The data show a dual size distribution of the krypton bubbles. In samples annealed up to 620 K and subsequently cooled, the larger bubbles melt in a pressure-broadened transition at 114–118 K. The smaller bubbles remain solid upon heating but, as a result of a roughening transition on the aluminum facets of the cavities, the Kr crystallites gradually lose their epitaxial alignment.

The vibrational electron energy-loss spectrum of the Si(111)(7×7) surface exhibits a well defined loss at 570 ${\mathrm{cm}}^{\mathrm{-}1}$ and a structure at 200–270 ${\mathrm{cm}}^{\mathrm{-}1}$. A similar spectrum is displayed by a Si surface with a pseudo (1×1) structure. Ab initio calculations of the dynamical matrix show that these features are due to localized vibrations involving Si adatoms and the surface atoms lying underneath. The latter are fivefold coordinated Si atoms exhibiting the electronic structure of an acceptor impurity localized at the surface.

Using infrared-visible sum-frequency generation as a probe, we have obtained the vibrational spectrum of a monolayer of pentadecanoic acid on a water surface in the CH stretch region. We have monitored the molecular orientation at different surface densities. It was found that the molecules in the liquid condensed phase have their alkane chains extended and oriented nearly normal to the surface, while in the liquid expanded phase the chains are highly disordered.

Predictions of mode-coupling theory for a schematic model of molten salts are shown to be consistent with recent neutron spin-echo experiments on ${\mathrm{K}}_{0.6}$${\mathrm{Ca}}_{0.4}$(${\mathrm{NO}}_3$${)}_{1.4}$. The theory relates the strong increase of viscosity fitted by η∝(T-${\mathrm{T}}_0$${)}^{\mathrm{-}\gamma }$ to the slow time decay of density fluctuations predicting a scaling function f(t/τ) with τ∝η. For t≳τ, f(t/τ) is well represented by exp[-(t/τ${)}^{\mathrm{\beta }}$] with β=0.56 in good agreement with experiment.

The nonlinear interaction of 532-nm, 100-ps laser pulses with KBr crystals is monitored up to damage by measurement of the σ component of the self-trapped exciton luminescence versus photon flux. The temperature rise in the interaction volume is obtained from the relation between σ luminescence and flux with use of the known temperature dependence of the luminous efficiency. The mechanism of energy deposition is four-photon free-carrier generation and free-carrier heating with other small contributions. Damage occurs at a temperature very close to the melting point.

Low-temperature, high-field deHaas–van Alphen measurements are presented which show that the conduction-electron mass in the Kondo lattice ${\mathrm{CeB}}_6$ decreases strongly with field. This field dependence is consistent with recent specific-heat results. The geometry of the Fermi surface does not depend on field. Thus we observe a reduction in the many-body enhancement of the electronic density of states at the Fermi energy which is described by a change of the itinerant-electron mass alone; the number of particles and the occupation of states in k space remain unchanged. We argue that ${\mathrm{CeB}}_6$ represents a different limit of heavy-fermion behavior as compared to ${\mathrm{UPt}}_3$.

Elastic, quasielastic, and inelastic neutron scattering measurements in ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ reveal novel two-dimensional antiferromagnetic behavior. At high temperatures the spins are ordered instantaneously over long distances two dimensionally but there is no measurable time-averaged staggered moment. The energy scale of the spin fluctuations is large, corresponding to an effective dispersion of ≳0.4 eV Å. The relevance to the high-temperature superconductivity in this class of materials is noted.

We study systems consisting of several maximally charged, nonrotating black holes (‘‘Reissner-Nordstrom’’ black holes) interacting with one another. We present an effective action for the system in the slow-motion, fully strong-field regime. We give an exact calculation of black-hole–black-hole scattering and coalescence in the slow-motion (but strong-field) limit.

The organization, encoding, and hierarchical construction of a generic chaotic attractor is presented. A systematic calculation of the multifractal properties is accomplished, and an understanding of the spectrum of singularities is reported. In general we expect nontrivial phase transitions in the thermodynamic formalism of strange attractors.