We propose a facile method to transform alignment of molecular rotation in a beam into transverse orientation with high efficiency via the second-order Stark effect in a homogeneous electric field scrE. The calculated J-orientation magnitude for a specific rotational level J exhibits a regular structure of equidistant dispersion-form signals in scr${\mathbf{E}}^2$ coordinates. Estimates performed for the NaK molecule show the possibility to produce rotational and isotopic selective J orientation for a fixed beam velocity v. The orientation appears in the direction perpendicular to the (v,scrE) plane, and the optimal angle between v and scrE is 45°.

We present the first angle-dependent energy spectra for the basic autoionization process ${\mathrm{He}}^{\mathrm{*}}$($2^3$S)+H($1^2$S) leading to Penning ionization (→He+${\mathrm{H}}^{+}$+${\mathit{e}}^{\mathrm{-}}$; PI) and associative ionization [→${\mathrm{HeH}}^{+}$(${\mathit{v}}^{+}$,${\mathit{J}}^{+}$)+${\mathit{e}}^{\mathrm{-}}$; AI]. Our results include electron energy spectra for both reaction channels and the ${\mathrm{H}}^{+}$-ion energy spectra for PI. The variation of the electron spectra with angle demonstrates the presence of substantial contributions from non-s-type electron partial waves, with the angle-dependent electron signals due to AI yielding clear information on the internal electron angular distribution of the autoionizing quasimolecule.

We present a theory explaining from a general point of view the intensity anomalies (magic numbers) in the mass spectra of metallic clusters. The transition from the electronic (super)shell structure in the mass spectra of smaller clusters to an atomic shell structure in the mass spectra of larger clusters is discussed in detail, including the dependence on temperature and cluster size. Results are given for the shell structure in the cohesive energy, the ionization potential, and photoyield which are useful for distinguishing between the two kinds of structure.

An adiabaticlike approximation is derived for the optical Bloch equations, extended for dense media, and used to interpret recent numerical results for the resonant interaction of ultrashort pulses with dense media. It is shown that dense media can exhibit behavior analogous to adiabatic following and adiabatic inversion. In particular, we show that dense collections of two-level systems can be adiabatically inverted by intrinsic self-chirping.

Recently formulated techniques for controlling chaotic dynamics face a fundamental problem when the system is high dimensional, and this problem is present even when the chaotic attractor is low dimensional. Here we introduce a procedure for controlling a chaotic time signal of an arbitrarily high dimensional system, without assuming any knowledge of the underlying dynamical equations. Specifically, we formulate a feedback control that requires modeling the local dynamics of only a single or a few of the possibly infinite number of phase-space variables.

It is argued that for d>1, chaotic systems with a conserved quantity can exhibit generic scale invariance—algebraic decay of spatial correlations without the tuning of external parameters—with exponents analytically calculable from noisy nonchaotic models. Numerical confirmation of these predictions for a specific coupled map system is presented.

We show that the time-independent disordered solid-melt patterns induced on silicon thin films by a continuous laser beam possess a characteristic length scale Λ which varies with irradiance ${\mathit{I}}_0$ as ${\mathit{I}}_0^{\mathrm{-}1/3}$ in agreement with a model based on heat flow, interfacial surface tension, and the reflectivity difference of the solid and melt. When ${\mathit{I}}_0$ is varied so that Λ decreases to a value comparable to λ, optical interference effects enhance (reduce) power deposition in molten (solid) regions, forcing a transition to a grating structure with orientation parallel to the polarization of the light beam and locking the length scale to Λ=λ.

A novel wall model, including inelastic fluid-wall collisions, molecular structure of the wall, and a long-ranged fluid-wall interaction, is used in molecular dynamics simulations of flow in two dimensions. For strong fluid-wall attraction the fluid velocity goes smoothly to zero at the wall; there is no velocity slip. In less dense fluids the velocity drops to zero in an ever-narrower region. Our results differ from standard kinetic theory but agree with Eu’s theory [Phys. Rev. A 36, 400 (1987)]. The nature of the fluid-wall interaction is important; repulsive walls give velocity slip.

A ponderomotive force associated with a uniform electromagnetic wave propagating in a medium with time varying dielectric properties [e.g., ε=ε(x-${\mathit{v}}_0$t)] is identified. In particular, when a laser ionizes a gas through which it propagates, a force is exerted on the medium at the ionization front that is proportional to (∇ε)${\mathit{E}}^2$ rather than the usual (ε-1)∇${\mathit{E}}^2$. This force excites a wake in the plasma medium behind the ionization front. The ponderomotive force and wake amplitude are derived and tested with 1D particle-in-cell simulations.

Brillouin enhanced four-wave mixing and phase conjugation of microwaves in an unmagnetized hydrogen plasma are observed. Transient and steady-state responses of the plasma and the phase conjugate wave are presented. Low-power, low-density operation agrees well with predictions of simple two-fluid plasma theory.

It is shown that if κ=${\mathrm{\omega }}_{\mathit{S}}$/${\mathrm{\omega }}_{\mathrm{LH}}$>1 (${\mathrm{\omega }}_{\mathit{S}}$ and ${\mathrm{\omega }}_{\mathrm{LH}}$ are the shear and lower hybrid frequencies), a sheared electron cross-field flow excites the electron-ion-hybrid mode, causing significant perpendicular ion acceleration. The electric potential develops coherent structures (vortexlike) longer than the electron Larmor radius, ${\mathrm{\rho }}_{\mathit{e}}$. For κ<1, a smooth transition occurs where the wavelength becomes of the order of ${\mathrm{\rho }}_{\mathit{e}}$, the lower hybid drift instability dominates, and the formation of vortexlike structures is no longer observed. The results are relevant to laboratory, laser-produced, and space plasmas.

A 0.5-μm-thick beryllium foil is heated by thermal x rays from a laser-irradiated converter foil up to temperatures of a few 10 eV. During the transformation of the solid Be into an ionized gas time-resolved absorption spectra have been measured in the region 100 eV ≲hν≲250 eV. The measurements agree well with calculations of the radiation transport, for which electron-impact line broadening was found to be essential. Smoothing of the Be K edge observed in the beginning of the heating, when the foil is still in a partially degenerate state, is attributed to thermal smoothing of the Fermi edge.

We have determined the electron energy distribution function (EEDF) in a low pressure nitrogen rf discharge both experimentally and using a computer simulation. The EEDFs show unusual structures, which can be interpreted in terms of a sheath-oscillation electron heating mechanism. However, the simulation shows that contrary to the conventional model, the electrons are heated in part by retreating sheaths. We present an analytical treatment of this phenomenon.

The axisymmetric, incompressible, viscoresistive magnetohydrodynamic equations for purely poloidal currents I(r,z) are transformed into three coupled scalar partial differential equations. These show that finite ∂I/∂z acts as a volumetric source of fluid ‘‘vorticity’’ which drives strong poloidal flows (jets).

Changes in nucleation and phase formation sequence with temperature may strongly affect the morphology of the final phase. The Si(111)-(√3 × √3 )Ag structure develops directly from the clean (7×7) structure at lower temperatures (500–700 K). Preferred nucleation at step edges and (7×7) domain boundaries reduces the effective dimensionality of the substrate and explains anomalies in domain size scaling observed by Zuo and Wendelken. An intermediate three-domain (3×1) structure precedes the √3 structure at higher temperatures, leading to a complete change in √3 nucleation and growth, as well as final domain size distribution and total Ag coverage.

The reaction between ${\mathrm{H}}_2$S and preabsorbed O on Ni(110) has been studied at the atomic level by means of scanning tunneling microscopy (STM). During the reaction, the initial flat (2×1)O structure is replaced by an intermediate rough surface with many small islands and troughs, all covered with a c(2×2)S overlayer. Most surprisingly, this metastable phase converts into the thermodynamically stable (4×1)S reconstructed phase. A new mechanism to activate a surface at the atomic level is suggested.

Pressure-induced orientational ordering transitions in solid molecular hydrogen and its isotopes are determined by path integral Monte Carlo methods. Effective interactions among molecules in the solid are calculated in the local density approximation. Unlike previous calculations which have systematically underestimated the ordering densities for this system, the present-treatment affords a calculation of the phase diagrams of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ in excellent agreement with experiment for orientational ordering up to a pressure of 100 GPa.

We demonstrate simultaneous high energy resolution (rms≊800 eV) measurements of ionization and phonons created by particle interactions in a semiconductor crystal of macroscopic size (60 g germanium) at 25 mK. We present first studies of charge collection at biases below 1 V/cm, and find that, contrary to commonly held opinion, the full recoil energy of particle interactions is recovered as phonons when charge trapping is negligible. We also report an unanticipated correlation between charge collection and phonon energy at very low bias, and discuss this effect in terms of charge trapping.

Positronium annihilation spectroscopy has been used to study capillary condensation of nitrogen adsorbed in mesoporous VYCOR glass. The temperature and pressure dependence of the relative change in the 3γ:2γ annihilation ratio are reported. Both isobars and isotherms exhibit features which are associated with a shifted gas-liquid transition. The isotherm data suggest that pore filling occurs via progressive layer formation at the pore surface followed by an abrupt gas-liquid phase transition at some pressure below the bulk saturated vapor pressure. Such a picture is consistent with the theoretical treatment in individual pores.

A new class of interface growth models is proposed, where global equilibration of the driving force is achieved between each local deposition. Two such models are studied numerically, and it is seen that roughness can occur with higher exponents than in situations where global equilibration of the driving force is not established. In particular, we have found a new universality class of growth models which in one dimension gives self-affine interfaces with roughness exponent χ=0.63±0.02.