Parity mixing of electron states should be extremely strong for heliumlike uranium. We calculate its size and discuss whether it could be determined experimentally. We analyze one specific scheme for such an experiment. The required laser intensities for two-photon spectroscopy of the $2^3$${\mathit{P}}_0$–2 ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$level splitting is of the order of ${10}^{17}$ W/${\mathrm{cm}}^2$. A determination of parity mixing would require at least ${10}^{21}$ W/${\mathrm{cm}}^2$.

Measurements of the ratio R between double- and single-ionization cross sections for antiproton impact on He, Ne, and Ar targets are reported for impact energies ranging from 65 keV to 20 MeV. At high energies the results are found to merge with proton results at around 20 MeV, and the high-energy limit of the common ratio is in good agreement with recent first-Born-calculation results for the helium target. The large difference previously observed in the ratio R for protons and antiprotons at energies between 0.5 and 5 MeV is found to persist down to the lowest energies investigated here.

Calculations are presented showing the influence of foil inhomogeneities upon the mean energy loss of molecular ions transmitted through thin films. They indicate that, due to the strong dependence of the transmission of molecular ions on thickness, previous measurements of the stopping of such ions at low bombarding energies can be affected by thickness variations of the foil.

The spectra of electrons ejected in collisions of protons and antiprotons with helium at impact energies of 100 and 500 keV are reported and compared. These calculations extend recent studies of the electronic spectra by means of the classical-trajectory Monte Carlo method to consider more energetic ejected electrons. Specifically, these new calculations exhibit the well-known binary peak, around which protons and antiprotons are shown to yield similar results. On the other hand, as predicted by quantum-mechanical distorted-wave approximations, a clear dip or anticusp is found in the electronic spectra produced by antiproton impact at electron velocities close to the projectile velocity, unlike the enhancement or cusp found for proton impact. Our results are consistent with simple dynamical mechanisms that reflect the two-center nature of the collision.

A theoretical study of the ionization of He(n=14 ${}_{}{}^1{}_{}{}^{}P$) atoms in thermal collisions with ${\mathrm{NH}}_3$ was carried out within the semiquantal approximation. The charge-dipole Glauber differential cross section was employed for the electron-molecule rotational deexcitation process. Calculated thermally averaged cross sections show quite a strong n dependence, especially for n≤17. A comparison is made between the present results and recent experiments.

One-perturber line shapes obeying detailed balance have been calculated for the sodium D line broadened by argon at 450 K using previously derived quantum-mechanical and classical-path methods. Agreement between line shapes calculated with both methods is excellent throughout the line profile. Decomposition of the configuration average in both methods shows that state-resolved line profiles are qualitatively similar. Quantitative agreement occurs only after averaging over initial conditions.

It is found that the field of the combined mode of the probe wave and the phase-conjugate wave in the process of degenerate four-wave mixing exhibits higher-order squeezing to all even orders. The degree of squeezing increases with the order N, and the higher-order squeeze parameter $q_N$ may approach -1.

The x-ray line spectrum of hydrogenlike chromium has been observed on the Frascati tokamak (FT) by means of a high-resolution bent-crystal spectrometer. The relative positions and line intensities of the resonance Lyman-α doublet and of all the dielectronic satellite lines have been compared with the wavelengths and intensity factors calculated by several authors. The results show an overall good agreement with the theory.

We consider the conformation of ionomers that carry metallic groups at each monomer site. This metallic group forms a point dipole in a nonpolar solvent. In the presence of a strong electric field, the dipoles are expected to align themselves in the direction of the external field. In this limit, the exact renormalization-group method yields the relation between the end-to-end distance R and the chain length N as R=$N^{\nu }$ with ν=2/d for 2≤d<4. The chain is thus fully stretched in two dimensions. A modified Flory theory also yields the same result. The relevance of our results to experiments is also discussed.

The Raman activity of low-frequency (20–300 ${\mathrm{cm}}^{\mathrm{-}1}$) vibrational modes of dehydrated, oriented fibers of the sodium salts of poly(dA)⋅poly(dT) and random sequenced DNA have been measured. Distinct bands near 60, 75–100, and 125–140 ${\mathrm{cm}}^{\mathrm{-}1}$ are resolved in poly(dA)⋅poly(dT). The Raman activity of the two lowest bands correlate with the previously observed infrared activity of poly(dA)⋅poly(dT). The apparent reduction in spectral line broadening for poly(dA)⋅poly(dT), as demonstrated by this and previous measurements of a number of different polynucleotides, is considered as possible evidence for inhomogeneous line broadening.

We discuss the effect on two-dimensional bubble growth of deviations in internal vertex angles from the predicted 120°. We also present evidence that Plateau border broadening contributes to the anomalous growth exponent that we have previously observed in froth coarsening.

We comment on two points related to the recent Brief Report by Yang, Chan, and Lieber [Phys. Rev. A 39, 5422 (1989)].

We calculate the phase distribution of a highly squeezed state using both a definition of a phase eigenstate and the area-of-overlap principle. This probability curve undergoes a transition from a single- to a double-peaked distribution when we decrease the product of squeeze and displacement parameters.

The existence of a universal reduced potential valid for all diatomic molecules has been predicted on a theoretical basis and verified using Rydberg-Klein-Rees (RKR) potentials. The reduced RKR potentials for various molecules have been shown to coalesce into virtually a single curve when they are plotted against z=${\mathit{z}}_1$ +(1/2(1-‖${\mathrm{\beta }}_1$‖)${\mathit{z}}_1^2$+1)2 (${\mathrm{\beta }}_2$-(1/4${\mathrm{\beta }}_1^2$-‖${\mathrm{\beta }}_1$‖+ 2)/3)${\mathit{z}}_1^3$, where ${\mathit{z}}_1$=√Δ (R/${\mathit{R}}_{\mathit{e}}$-1) and ${\mathrm{\beta }}_{\mathit{l}}$r=${\mathit{a}}_{\mathit{l}}$/${\mathrm{\Delta }}^{\mathit{l}}$/2. The Morse curve [1-exp (-z)${]}^2$-1 is found to represent the universal curve well. Here R is the internuclear distance, Δ is the Sutherland parameter, and ${\mathit{a}}_{\mathit{l}}$ are the Dunham coefficients.

Experimental confirmation of stimulated Raman scattering (SRS) in micrometer-sized droplets supported simultaneously by resonances at the incident (input) laser wavelength and at the emitted (output) SRS wavelength is provided. Identified mode orders of contributing input resonances increase with droplet radii over the size range investigated (∼5.4–7.4-μm radius). Measured SRS spectra reveal that the mode order of the input and output resonances coincide in 90% of the cases studied.

When a wettable solid substrate (flint glass) is brought into contact with a vessel of water on the surface of which an appropriate surfactant has been spread (valinomycin), a visible film is observed to creep up to the substrate. If the substrate is now bent so that its far end makes contact with a second water vessel (at the same height) on which the same surfactant is spread, a net flow of surfactant is observed to occur under the influence of a surface tension differential between the two vessels. From elementary hydrodynamics the thickness of the film of water accompanying the surfactant flow can be deduced from measurements of the surface tension differential and the rate of transfer of the surfactant. We have developed a theory for the thickness of this entrained film, which turns out is governed by the van der Waals dispersion force. Our treatment allows us to deduce the film thickness from first principles and, by comparison with the experimental results, to determine the retarded Hamaker constant B.

Transfer of a monolayer (valinomycin) between two Langmuir troughs via an interconnecting glass ‘‘bridge’’ has been observed when there is a difference between the monolayer pressures in the two troughs. Assuming that the transfer occurs over the surface of the thin film of water that wets the ‘‘bridge,’’ the transfer rate can be used to estimate the thickness of the liquid film. The thickness thus determined may be used to determine the retarded van der Waals (Hamaker) constant associated with the interaction of the film with the underlying substrate.