The vibrational temperature, $T_v$, of ${\mathrm{N}}_2^{+}$ and ${\mathrm{O}}_2^{+}$ ions drifting in a helium buffer has been determined for the first time quantitatively as a function of $\frac{E}{N}$. For both ions $T_v$ reaches ∼ 3000 K at $\frac{E}{N}\simeq 150\times {10}^{17}$ V·${\mathrm{cm}}^2$. This result resolves various previously inexplicable aspects of the behavior of ion-neutral reactions as a function of energy.

Evidence is presented for nonresonant and resonant electron transfer and projectile $K$ x-ray excitation in 15-94-MeV ${\mathrm{Si}}^{11+}$ + He collisions. In the former, the projectile $K$ electron is excited by the Coulomb field of the target nucleus, and a target electron is captured. In the latter, the electron-electron interaction gives rise to the resonant process. The nonresonant process reached its maximum cross section at ∼20 MeV, while the resonant process peaked at ∼85 MeV, in agreement with theory.

By use of circularly polarized synchrotron radiation at BESSY, spin-polarized photoemission from the valence orbitals of Xe and Kr atoms adsorbed on the Pt(111) single-crystal surface has been studied. Under certain conditions almost complete photoelectron polarization parallel or antiparallel to the photon spin was observed, allowing a direct assignment of quantum numbers of the states involved. Highly resolved intensity and polarization spectra in the threshold region exhibit pronounced variations versus photon energy.

The exchange of photons between single Rydberg atoms and a single mode of a superconducting cavity with a quality factor $Q=8\mathrm{}\times {10}^8$ at 2 K was observed. Signals could still be detected with an average number of only 0.06 atom simultaneously in the cavity. With one Rydberg atom the linewidth of the maser transition at about 21 GHz was power broadened and at higher densities asymmetry of the transition was observed, which is ascribed to an ac Stark effect.

We show experimentally that for the electrohydrodynamic instability in nematic liquid crystals the threshold for the onset of spatial turbulence can be increased by at least a factor of 2 by superimposing noise on the applied voltage. We find that for sufficiently high noise intensities a direct transition from the spatially homogeneous state to turbulence via intermittency can be induced.

Finite-beam, two-dimensional particle simulations of single- and double-frequency laser-plasma heating are presented. In the single-frequency case, Raman backscatter and side scatter initially heat the plasma. Even in the absence of strong forward Raman scattering, strong subsequent electron heating is observed. When two collinear laser beams with $\Delta \omega ={\omega }_p$ are used, a coherent plasma wave heats the electrons to many megaelectronvolts. In the latter case, ion dynamics eventually disrupts the heating process.

Molecular hydrogen in hydrogenated amorphous silicon has been observed directly in the NMR spectrum, occurring as a powder-averaged Pake doublet in the orientationally ordered state. The molecular ${\mathrm{H}}_2$ content is found to be approximately 0.25 at.% and to increase on annealing to about 1 at.%. In both cases, the ${\mathrm{H}}_2$ orientationally orders and solidifies at temperatures considerably higher than in pure, normal ${\mathrm{H}}_2$, because of the additional forces exterted on the ${\mathrm{H}}_2$ by the $a$-Si container.

Results from a LEED analysis of NiAl(110) demonstrate that it possesses a large rippled relaxation away from its hypothetical truncated bulk surface, with the Al sites of the top composite Ni-Al layer being displaced approximately 0.22 Å above the Ni sites. The evidence for this rippling is strong, since the agreement achieved between calculated and experimental $I-V$ profiles is of the same quality obtained in better LEED analyses of monatomic surfaces.

It is shown by a simple model calculation that the ionic solids in the CsCl phase transform discontinuously to a tetragonal phase under high pressures at a fractional volume in the neighborhood of 0.5. This general result follows as a consequence of competing Madelung energy and repulsive energy terms. The $\frac{c}{a}$ variation with pressure and transition volume fraction are in approximate agreement with the recent ultrahigh pressure experiments on cesium halides.

The heat of two-dimensional evaporation of gold on a tungsten (110) surface is derived from the temperature dependence of the work-function change at constant submonolayer coverage. It shows a temperature dependence as expected for a roughening transition of the island edges at $T_R=0.57\mathrm{}{T}_c^{2\mathrm{D}}$.

The $H$ and $T$ dependence of the magnetic Bragg peak intensity has revealed a relatively sharp metastability boundary $T_F\mathrm{}\left(H\right)\mathrm{}$ in a $d=2\mathrm{}$ random-field (RF) Ising system: ${\mathrm{Rb}}_2$${\mathrm{Co}}_{0.85}$${\mathrm{Mg}}_{0.15}$${\mathrm{F}}_4$. Remarkably, $T_F\mathrm{}\left(H\right)\mathrm{}$ scales as $T_{\mathrm{N}}-T_F\mathrm{}\left(H\right)\mathrm{}\propto H^{\frac{2}{\phi }}$, with the RF crossover exponent $\phi =1.74\mathrm{}\pm 0.02$, and lies just inside the RF crossover region. Freezing must therefore be tied to RF critical behavior. The approach of the system to equilibrium at $T_F\mathrm{}\left(H\right)\mathrm{}$ proceeds logarithmically with time.

We present a theory of the collective excitation spectrum in the fractional quantum Hall-effect regimes, in analogy with Feynman's theory for helium. The spectrum is in excellent quantitative agreement with the numerical results of Haldane. Within this approximation we prove that a finite gap is generic to any liquid state in the extreme quantum limit and that in this single-mode approximation gapless excitations can arise only as Goldstone modes for ground states with broken translation symmetry.

Temperature-dependent (20-300 K) electron-energy-loss measurements of the quasielastic peak for ∼2.5-10 Å of evaporated Au and Pd on Si(111) are presented, which, together with a theory of the electron scattering from metallic layers, permit the determination of dc conductivities. Metallic films, ∼ 10 Å thick, are found to have large temperature-independent resistivities dominated by surface scattering and imperfections. An unusual temperature-dependent resistivity is found for Pd on Si which is suggested to arise from a phase transition near the interface.

Novel behavior of the one-dimensional incommensurate Schrödinger equation when the potential is derived from a Kolmogorov-Arnol'd-Moser torus is found by exploitation of univeral scaling properties. Our numerical investigation reveals in particular that nearly torus-breaking electronic states undergo series of back-and-forth localization transitions in sensitive dependence on the potential strength.

We show that image-potential surface states are strongly affected by surface corrugation. In particular, their binding energy and effective mass are strongly coupled. New inverse-photoemission measurements for Ag(100) indicate that neglect of the corrugation contribution to the binding in previous work has caused (i) the confusion of the fundamental and excited image states and (ii) underestimation, by a factor of 3, of the spatial extent of the states observed.

One-phonon distorted-wave Born-approximation calculations of the energy-dependent phonon-assisted sticking probabilities of ${\mathrm{H}}_2$ and HD at smooth metal surfaces yield peaks as a function of incident energy due to rotationally mediated selective-adsorption resonances. These peaks are weak for ${\mathrm{H}}_2$, but are strong (and observable) for HD because the asymmetry of the molecule causes stronger translational-rotational coupling.

The synthetic equivalents of the paramagnetic states of the active sites of the ferredoxin and high-potential ${\mathrm{Fe}}_4$${\mathrm{S}}_4$ proteins have been created in single crystals. This has been accomplished by induction of in situ redox reactions by ionizing irradiation in the crystal of the compound chosen to be initially in the diamagnetic state. This opens the way for detailed studies with ESR of the magnetic and electronic properties of these important polymetallic iron-sulfur cores.

In the context of stochastic quantization of field theories we propose a method to make analytic computations of critical exponents and we evaluate them for ${\left({\phi }^2\right)}_3^2$. It consists of regularization of the theory by use of a convenient non-Markovian process, where nonlocality in time is measured by the regularizing parameter $\sigma$. For a fixed dimensionality there is a value of $\sigma$ where the theory is renormalizable and asymptotically free in the infrared, allowing a perturbative expansion around it.

Noting that quantum measurements are in general incomplete, we develop, starting from a recent entropic formulation of uncertainty, a maximum uncertainty principle to define the statistical mechanics of microscopic systems. The resulting ensemble entropy coincides with the expression of von Neumann, thus providing a unified, quantum basis for statistical physics of all systems. Examples involving momentum and position measurements are discussed.

The masses, total widths, and leptonic widths of three triplet $s$-wave $b\overline{b}$ states $\Upsilon \mathrm{}\left(4S\right)\mathrm{}$, $\Upsilon \mathrm{}\left(5S\right)\mathrm{}$, and $\Upsilon \mathrm{}\left(6S\right)\mathrm{}$ are determined from measurements of the $e^{+}{e}^{-}$ annihilation cross section into hadrons for $10.55<W<\mathrm{}11.25\mathrm{}$ GeV. The resonances are identified from potential model results and their properties are obtained with the help of a simplified coupled-channels calculation. We find $M\left(4S\right)=10.577\mathrm{}$ GeV, $\Gamma \mathrm{}\left(4S\right)=25\mathrm{}$ MeV, ${\Gamma }_{\mathrm{ee}}\mathrm{}\left(4S\right)=0.28\mathrm{}$ keV; $M\left(5S\right)=10.845\mathrm{}$ GeV, $\Gamma \mathrm{}\left(5S\right)=110\mathrm{}$ MeV, ${\Gamma }_{\mathrm{ee}}\mathrm{}\left(5S\right)=0.37\mathrm{}$ keV; $M\left(6S\right)=11.02\mathrm{}$ GeV, $\Gamma \mathrm{}\left(6S\right)=90\mathrm{}$ MeV, ${\Gamma }_{\mathrm{ee}}\mathrm{}\left(6S\right)=0.16\mathrm{}$ keV.