The conduction-electron spin-scattering cross sections of krypton and xenon atoms adsorbed on a lithium surface were determined by measurement of the conduction-electron spin-resonance linewidth of lithium films as a function of rare-gas coverage. The results indicate that there is a large pileup of conduction-electron density deep within the rare-gas adsorbate core, in agreement with current theoretical calculations of the electronic structure of rare-gas-on-metal systems.

A Monte Carlo study of high-field electronic transport in silicon dioxide is undertaken. Contrary to previous theoretical studies, we do not model the electronic structure by a single free-electron-like band. Our model accounts for a set of satellite valleys which contribute density of states needed for effective scattering at a few electronvolts. We find that the electronic distribution is stable for fields on the order of 10 MV/cm.

The electric field gradient can be obtained from self-consistent energy-band calculations by the linearized-augmented-plane-wave method provided that a general potential is used. This first-principles method, which does not rely on any Sternheimer antishielding factor, is tested for ${\mathrm{Li}}_3$N and yields electric field gradients for Li(1), Li(2), and N in excellent agreement with NMR experiments. The electric field gradient is mainly determined by local distortions of the electronic charge density, especially in the case of the polarizable ${\mathrm{N}}^{3-}$ ion.

We consider the effect of inelastic scattering on tunneling resonances in one dimension using a Breit-Wigner scattering formalism. We show that the peak transmission at resonance is decreases by the ratio of the intrinsic resonance width to the inelastic-scattering rate. For disorder-localized one-dimensional systems this predicts that resonant-tunneling conduction, in addition to variable-range-hopping conduction, will be observable at temperatures below 0.01 K in present experimental systems.

The homogeneous Bianchi and Kantowski-Sachs metrics of relativistic cosmology are investigated through their correspondence with recent geometrical results of Thurston. These allow a partial classification of the topologies for closed, locally homogeneous spaces according to Thurston's eight geometric types. Besides, we learn which of the Bianchi-Kantowski-Sachs metrics can be imposed on closed spatial sections of cosmological models. This is seen as progress toward implementation of a postulate of the closure of space for both classical and quantum gravity.

The first frequency standard based on laser-cooled atoms is reported. Beryllium atomic ions were stored in a Penning trap and cooled by radiation pressure from a laser. The frequency of the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}_{}^{+}{}_{}{}^{}$ $(M_I, M_J)=(-\frac{3}{2}, +\frac{1}{2})\leftrightarrow (-\frac{1}{2}, +\frac{1}{2})$ ground-state hyperfine transition at its magnetic-field-independent point was determined to be 303 016 377.265 070 (57) Hz. The accuracy of a frequency standard referenced to this transition was comparable to the best frequency standards, which are based on cesium atomic beams.

We have measured total cross sections for single electron capture by fully stripped carbon, nitrogen, and oxygen ions from atomic hydrogen, in the energy range 3-7.5 keV/u. Some results for incompletely stripped ions are shown for comparison. For ${\mathrm{C}}^{6+}$ and ${\mathrm{N}}^{7+}$ we have also determined line-emission cross sections for several $\Delta n=1, 2$ transitions. All results are in excellent agreement with recent theoretical calculations.

We have observed, for the first time in highly ionized atoms, electric quadrupole transitions between the $3p$ and $2p$ levels of fluorinelike and neonlike ${\mathrm{Xe}}^{45+}$ and ${\mathrm{Xe}}^{44+}$. We have made precision measurements ($\frac{\lambda }{\Delta \lambda }=2\mathrm{}\times {10}^4$) of the relative wavelengths of the allowed electric dipole ($E1\mathrm{}$) transitions and the forbidden electric quadrupole ($E2\mathrm{}$) transitions connecting the $n=3\mathrm{}$ and the $n=2\mathrm{}$ levels. We have also derived from these measurements several $\Delta n=0\mathrm{}$ intervals between states of opposite parity.

A large optical Stark effect has been observed in the two-photon spectrum $X{}_{}{}^2{}_{}{}^{}\Pi \to A{}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ in nitric oxide. It is explained as a near-resonant process in which the upper state of the two-photon transition is perturbed by interactions with higher-lying electronic states coupled by the laser field. A theoretical analysis is presented along with Stark parameters determined from ab initio wave functions. The synthetic spectrum reproduces the major experimental features.

The wavelengths of $1s^2{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}-1\mathrm{snp}{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ transitions in the two-electron ions Ar xvii and K xvii have been measured in solar-flare spectra. The QED contributions to the transition energies are determined by comparison of the measured transition energies to the calculated values. The ionization limit of Ar xvii is also determined.

We show that squeezed states can be generated by the interaction of coherent electromagnetic radiation with a plasma. Inside the plasma the electromagnetic field is represented by quasiphotons. The conditions for obtaining squeezed states in this system are related to dispersion relations of the quasiphotons in the plasma.

In a single-atom double-resonance experiment involving a strong and a weak transition, quantum jumps on the weak transition cause the fluorescence of the strong transition to turn on and off abruptly. The fluorescence is off when the weak transition is excited and on when it is not. Thus quantum jumps on the weak transition can be directly monitored by observation of the random telegraph signal radiated by the strong transition. We present here a simple theory of this effect for the case of incoherent excitation.

The nonlinear stability of drift-tearing modes in the presence of an electron temperature inhomogeneity is investigated. It is shown that linearly growing drift-tearing modes are rendered stable at a very small island width by quasilinear thermal effects. However, both linearly and quasilinearly stabilized modes grow to large amplitude if the initial island width is larger than the linear tearing layer, demonstrating the importance of nonlinear considerations in predictions of stability.

We report the first high-resolution study of the nematic twist coefficient, $K_2$, above the smectic-$A$ transition. The twist coefficient exponent, ${\rho }_2$, is in reasonable agreement with x-ray studies of smectic-$A$ correlation length exponents, i.e., ${\rho }_2\sim 2{\nu }_{\perp }^x-{\nu }_{\parallel }^x$, and in good agreement with the smectic dilation coefficient exponent, $\phi$. ${\rho }_2$ is less than the $x-y$ value and is nonuniversal.

Simultaneous magnetic-deformation and light-scattering studies of the nematic bend and twist constant exponents respectively suggest that the nematic-smectic-$A$ critical point is weakly anisotropic, in disagreement with all theories of the nematic-smectic-$A$ transition. This study also suggests that the bend exponent is universal and very close to the helium value.

The x-ray fluorescence, at the near-total external reflection configuration, was employed to study the concentration profile of a dissolved polymer near the liquid-gas interface. The determined experimental concentration profile conformed with a hyperbolic cotangent squared dependence with a concentration excess ratio of about 100:1 of the surface relative to the bulk. This experiment presents the first direct measurement of that kind at the air-liquid interface and demonstrates the effectiveness of this new method to study nondestructively interface structures on the scale of tens to hundreds of angstroms.

We have studied the aggregation of silica microspheres confined to two dimensions at an airwater interface. Under microscopic observation, both monomers and clusters are seen to aggregate by a diffusion-limited process. The clusters' fractal dimension is 1.20±0.15, smaller than values obtained from current models of aggregation. We propose that anisotropic repulsive interactions account for the low dimensionality by more effectively repelling particles from the side of an existing dendrite than from the end.

A quasiclassical approximation that we develop is used to obtain, in a simple way, the range of validity of the impulse approximation. We show that at energy transfers readily obtained in pulsed neutron sources, the neutron-scattering cross section for ions bound in a solid is accurately described by the impulse-approximation limit. A new and practical method of inverting the Radon transform that describes $S(q, \omega )$ in this limit is provided, that may be of use in other areas as well. The momentum distribution obtained in this way may be used to infer the interionic potential for light ions in a heavy host.

A new metastable phase of cobalt—body-centered cubic—has been synthesized by use of molecular-beam epitaxial growth to stabilize the crystal structure. Large (1×1 ${\mathrm{cm}}^2$) films have been grown on (110) GaAs and characterized by high-energy electron diffraction, Auger analysis, x-ray diffraction, magnetometry, spin-polarized photoemission, and ferromagnetic resonance. The results indicate a ferromagnetic material very similar to $\alpha$-Fe both electronically and magnetically, with a metastable lattice constant $a_0=2.827\mathrm{}$ Å. This technique provides a general approach for the realizing of metastable phases.

High-resolution infrared data of Si(100) surfaces saturated with H at room temperature show that the so-called 1×1 surface is in fact a disordered phase with roughly half the H bonded in monohydride (H-Si-Si-H) and half in dihydride (Si${\mathrm{H}}_2$) configurations. Upon saturation exposure at 380 K, the surface is ordered into a newly identified 3×1 phase, as evidenced by LEED, involving repeated alternating monohydride and dihydride units.