The authors compare predictions of a recent density-functional theory for adsorption of argon onto a solid-carbon-dioxide substrate with Monte Carlo simulations of exactly the same system. The basic predictions of the density-functional theory are shown to be qualitatively at variance with the simulation results. In particular, the simulations show predominantly monolayer adsorption, with a second layer forming at higher bulk densities. There is no sign of the thick structureless films predicted by the recent density-functional theory.

The authors investigate the form of a standing wave in a cold inhomogeneous electron plasma, taking into account "relativistic effects." The wave amplitude is greatly modified near the critical surface for high intensities.

The mean-spherical approximation for fluids is extended to treat the case of dense systems interacting via soft potentials. The extension takes the form of a generalized statement concerning the behavior of the direct-correlation function $c\left(r\right)\mathrm{}$ and the radial-distribution function $g\left(r\right)\mathrm{}$. From a detailed analysis that views the hard-core portion of a potential as a perturbation on the whole, a specific model is proposed which possesses analytic solutions for both Coulomb and Yukawa potentials, in addition to certain other remarkable properties. A variational principle for the model leads to a relatively simple method for obtaining numerical solutions.

An experimental study was undertaken to measure the optical Kerr effect (OKE) in liquids induced by picosecond laser pulses. The effects of different parameters on the dynamics of the OKE are described. The following parameters were investigated: the spatial and temporal profiles of the laser pulses, the intensity of the exciting laser pulse, the length of the Kerr gate, the concentration of the sample solution, the relaxation time of the sample, the temperature, and the pair correlation factor. The nonlinear indices of refraction of 29 neat liquids were measured and tabulated.

The conditions for oscillatory instabilities of nematic liquid crystals in steady electric and magnetic fields are established. For typical parameter values the critical electric field is calculated to be ∼20 statvolts/cm and the frequency of oscillation is ∼300 ${\sec }^{-1\mathrm{}}$. For this marginal state the large charge-focusing mechanism, which suppresses the exchange of stabilities, is inoperatiave.

A theoretical description of the single-mode dynamics of both the Rayleigh-Bénard instability (RBI) and the Soret-driven instability (SDI) is provided, starting from the general conservation equations and exploiting a technique similar to that used for the laser instability. A system of nonlinear dynamic equations is found to describe self-consistently both the RBI and the SDI. The single-mode steady-state solutions are derived without making use of perturbation expansions. A quantitative theoretical explanation is found to account for such recent experimental results as the saturation of the horizontally averaged concentration gradient at midheight in the SDI, the appearance of relaxation oscillations in RBI and SDI transients, and the dependence of the oscillation period on the temperature difference between the plates. The analogy with the laser suggests the possibility of observing giant pulses in the transient well above threshold, and of measuring pretransitional fluctuations of the mode which goes unstable. Connections with the Lorenz model are also discussed.

Deuterium magnetic-resonance studies of spectral patterns from spinning samples are made to measure the relative contribution of various orientational order mechanisms to the biaxiality of the hydrocarbon chain in the smectic $C$ phase. The detailed theory of motional averaging as applied to the spinning techniques is reported for the first time. Orientational order parameters measurable by this technique representing various aspects of molecular orientational order are discussed. The technique is applied to a particular compound $n$-heptyloxyazoxybenzene, where it is possible to distinguish between those order parameter which result from rotational biasing about the long molecular axis and those order parameters which do not. The temperature dependence of these order parameters in this fixed-tilt-angle system is then determined.

The authors investigate the statistical mechanics of a model Lagrangian involving a complex scalar field for which the equations of motion possess solitary-wave solutions due to phase anisotropy. Using a transfer-operator technique, the authors find that the low-temperature correlation length for the field grows exponentially with decreasing temperature, at a rate determined by the activation energy for the solitary wave. This activation energy exhibits a crossover from that for a purely real "${\phi }^4$" scalar kink to that for a phase-only sine-Gordon soliton as the magnitude of the anisotropy potential is decreased past a point where the exact solitary-wave solution is known to "bifurcate." It is concluded that these nonlinear excitations of the complex scalar field are "elementary" in the same sense as real scalar solitary waves are elementary excitations of real one-component fields.

The ideal-gas phenomenology of Currie and co-workers is extended to systems which bear solitary-wave excitations that are nontransparent to small oscillations. This extension enlarges the class of nonlinear systems which may be viewed at low temperatures as ideal gases of kinks and phonons. The authors treat the double-quadratic chain in detail, finding that the analysis can be carried quite far for this simple example system.

New data on the impact-parameter dependence of $K$- and $L$-x-ray production in ${}_{18}{}^{}{}_{}{}^{}\mathrm{Ar}$ + ${}_{50}{}^{}{}_{}{}^{}\mathrm{Sn}$ collisions reported by Fintz et al. and on $K$-x-ray production in ${}_{28}{}^{}{}_{}{}^{}\mathrm{Ni}$ + ${}_{50}{}^{}{}_{}{}^{}\mathrm{Sn}$ and ${}_{28}{}^{}{}_{}{}^{}\mathrm{Ni}$ + ${}_{82}{}^{}{}_{}{}^{}\mathrm{Pb}$ collisions by Johnson et al. are compared with molecular model calculations. The latter are based on the united-atom ionization model of Briggs, applied to the $3d\sigma$ molecular orbital and corrected for the dependence of the $3d\sigma$ binding energy on internuclear distance. Overall, reasonable agreement between theory and experiment is found.

The authors show that the laser bandwidth effects in resonance fluorescence at low intensities can be treated most readily in terms of simple convolutions, and further that this approach allows one to consider an incident field with an arbitrary spectral distribution, with or without the presence of atomic (line-broadening) collisions.

Multipole interference effects are predicted in the generalized cross sections, and in the ratio $\frac{{\hat{\sigma }}_C}{{\hat{\sigma }}_L}$ of the cross sections for circularly and linearly polarized laser light for the case of the two-photon ionization of the $n=2\mathrm{}$ singlet metastable helium atoms in the wavelength range 5036-5050 Å.

The Lamb shift of ${\mathrm{He}}^{+}$ is derived from the measured anisotropy in the electric-field-induced quenching radiation of the metastable $2s_{\frac{1}{2}}$ state. The results demonstrate that the anisotropy method can be applied with high precision to one-electron ion beams, as well as neutral beams. We find a Lamb shift of 14040.2±2.9 MHz (1 standard deviation). The sources of error and difficulties encountered in working with ion beams are discussed in detail.

The dependence of the long-range interactions between a Rydberg electron and an ionic core on the nuclear charge of the core is analyzed. It is pointed out that the nonadiabatic interaction will be most readily apparent in spectral-line measurements of systems belonging to the beryllium and boron isoelectronic sequences. A quantitative analysis is presented of data for Cl xiv.

The higher polarizabilities ${\gamma }_{\mathrm{zzzz}}$, $B_{zz:zz}$, and $C_{zz:zz}$ have been calculated for ${\mathrm{H}}_2$ using different-sized basis sets composed of James-Coolidge basis functions. The most-accurate wave functions led to the values 674, -89.8, and 5.97 a.u., respectively. It is emphasized that these properties are critically sensitive to wave-function quality.

Static polarizabilities and hyperpolarizabilities for molecules are investigated at the correlated level. The finite-field, coupled Hartree-Fock theory is used as a zeroth-order approximation, with correlation included by using the linked-diagram expansion and many-body perturbation theory, that includes single, double, and quadruple excitation diagrams. The theory is illustrated by studying the hydrogen fluoride molecule. It is demonstrated that the correlation effect for the hyperpolarizabilities $\overleftrightarrow{\beta }$ and $\overleftrightarrow{\gamma }$ can be quite large. The average polarizability and dipole moment of HF are in excellent agreement with experiment. The relative importance of the various types of diagrams contributing to electric field properties are discussed. The dependence of the computed hyperpolarizability on basis sets is also investigated.

The Sternheimer valence shielding and antishielding factor $R$ has been calculated for the isoelectronic series of atoms in $2p^1$, $2p^2$, $2p^4$, $2p^5$, $3p^1$, $3p^4$, and $3p^5$ electronic configurations by means of the uncoupled numerical Hartree-Fock method. A slightly larger shielding effect is observed for the ${}_{}{}^1{}_{}{}^{}D$ state relative to the ${}_{}{}^3{}_{}{}^{}P$ state for ${\mathrm{N}}^{-}$, O, and S. In the $2p^4$ series, where ${\mathrm{N}}^{-}$ is included, it is found that the mononegative ion is characterized by an $R$ which is twice as large as that for the isoelectronic neutral atom. The general trends observed in the variation of $R$ within an isoelectronic series are discussed.

The theory for direct elastic and inelastic collisions between composite atomic systems (ions or neutral atoms) is formulated within the framework of the Glauber approximation. It is shown that the phase-shift function $\chi$, which depends on the coordinates of all electrons in the projectile and target as well as on the impact parameter, is the sum of a point Coulomb contribution and a contribution which may be expressed entirely in terms of the known electron-hydrogen-atom and proton-hydrogen-atom phase-shift functions. The scattering amplitude is reexpressed in terms of an optical profile function which depends on the initial and final states of the atoms. The pure Coulomb scattering in the case of elastic collisions between ions is explicitly isolated and the additional effects of the long-range point Coulomb interaction in both elastic and inelastic collisions are exhibited. The exact optical profile function is approximated by a first-order expansion in Glauber theory which takes into account certain multiple collisions. The approximate optical profile function consists of two types of terms, one corresponding to interactions involving only one electron, the other to interactions involving two electrons, one from each atom or ion. The former is obtained in closed form in terms of Meijer $G$ functions. The latter is obtained as a one-dimensional integral. The scattering amplitude is thereby reduced from a [$3(M+N)+2\mathrm{}$]-dimensional integral, where $M+N$ is the total number of electrons in the projectile and target, to a two-dimensional integral. For collisions involving one or two neutral atoms, as in ion-atom or atom-atom collisions, the scattering amplitude is further reduced to a simple closed-form expression.

Self-consistent-field calculations have been performed for the $X{}_{}{}^1{}_{}{}^{}\Sigma$ state of ${\mathrm{Br}}^{-}$ + He and the $X{}_{}{}^2{}_{}{}^{}\Sigma$ and $A{}_{}{}^2{}_{}{}^{}\Pi$ states of Br + He. The potential-energy curves indicate a threshold for electron detachment of 7.2±1.2 eV. No indication of a collision mechanism for detachment at lower energies is found.