A continuous band structure resembling an unresolved pure rotation band was observed in the Raman spectrum of high-purity gaseous argon. The wavelength corresponding to the peak of the band structure shifts with temperature in agreement with the theoretical shift of the pure rotation band of a diatomic molecule. The value of the rotational constant is in good agreement with that derived from data on the second virial coefficient for argon.

We have employed newly developed graphite mosaic crystals to observe the $L$ x-ray spectrum from the decays of ${}_{}{}^{109}{}_{}{}^{}\mathrm{Cd}$ and ${}_{}{}^{125}{}_{}{}^{}\mathrm{I}$. From the measured values of the subshell fluorescence yields, we conclude that either one or both of the Coster-Kronig transitions $L_1-L_3{M}_4$ and $L_1-L_3{M}_5$ is forbidden in both the silver and tellurium daughters.

The fine-structure interval $\Delta \nu$ in the ground state of positronium has been remeasured with higher precision to obtain $\Delta {\nu }_{\mathrm{expt}}=203.396\mathrm{}\pm 0.005$ GHz (24 ppm). The current theoretical value is $\Delta {\nu }_{\mathrm{theor}}=203.4155\mathrm{}$ GHz. The difference $\Delta {\nu }_{\mathrm{expt}}-\Delta {\nu }_{\mathrm{theor}}=-19\mathrm{}\pm 5$ MHz is about 4 standard deviations of the experimental error, indicating the need for calculations of higher-order radiative contributions. Values are given for both the linear and quadratic coefficients of the fine-structure density shift in ${\mathrm{N}}_2$.

The discrepancies that exist between theory and experiment in the ground-state energy and the liquid structure function of ${\mathrm{He}}^4$ are not insignificant. We show via a two-dimensional Monte Carlo calculation that by incorporating explicit three-particle correlation factors into the variational wave function, both the energy and the liquid structure function are improved in the right direction. This suggests that the discrepancies need not be attributed to the choice of the potential.

In a thermally driven superfluid helium film the dissipation has been observed to saturate for sufficiently high superfluid velocity in agreement with the fluctuation model of intrinsic dissipation.

The force observed by Gamota and Barmatz, which is exerted upon the flexible diaphragm by a stream of charged vortex rings in superfluid helium, is shown to arise from the electric force applied to the rings rather than an impulse carried by the rings. Consequently, the diaphragm should not be a sensitive detector of uncharged vortices. Underlying the analysis is the fact that the charged rings do not obey the Helmholtz-Kelvin circulation theorem.

The characteristic whistler structure of oblique hydromagnetic shocks is observed experimentally to suffer from a rapidly growing short-wavelength instability, which is tentatively identified as the decay instability first predicted by Galeev and Karpman. It is suggested that this instability is responsible for the turbulent whistler shock structure observed when a super-Alfvénic plasma stream encounters a magnetic obstacle.

The penetration of a magnetic pulse into a cylindrical, field-free plasma has been studied under conditions where the penetration was determined by turbulent conductivity. The penetration time was found to vary as $\frac{{\left(M_i{n}_e\right)}^{\frac{1}{2}}}{B}$, where $M_i$ is the ion mass, $n_e$ is electron density, and $B_0$ is peak amplitude of the applied magnetic field. This corresponds to a mean conductivity $\sigma \propto \frac{M_i{n}_e}{B_0^{}{}_{}{}^2}$. These results can not be accounted for by any present theoretical model.

Negative-energy modes driven by a normal gradient of the electron temperature are found in two-dimensional equilibrium configurations such as the toroidal diffuse pinch. These modes tend to grow by transferring (positive) energy to the resonating electrons; they have properties that make them suitable to alter considerably the orbits of the deeply trapped electrons by proper resonant interactions, and make them lead to electron thermal energy transport across the magnetic field without corresponding particle transport.

We report computer simulations of critical slowing down in a two-dimensional kinetic Ising system consisting of a square $n\times n$ lattice with periodic boundary conditions. The results for the divergence of the relaxation times disagree with the predictions of the dynamical scaling hypothesis and with recent estimates obtained from a high-temperature expansion method.

Tunnel junctions were fabricated on ${\mathrm{Nb}}_3$Sn films reacted on Nb substrates. Derivative measurements were made from 0 to 50 meV and above 18 K. From these tunneling results, the phonon spectrum of ${\mathrm{Nb}}_3$Sn is shown to have a strong low-energy peak at 9 meV, a broad peak centered around 17 meV, and a small peak at 25 meV. Using this shape of the phonon spectrum and taking ${\mu }^{*}=0.11\mathrm{}$, a maximum $T_c$ of ∼ 21 K is obtained for this class of superconductors. This result suggests that crystal transformations arising from instabilities do not limit $T_c$ in this case.

The electric field gradient in stressed NaCl is calculated using a simple cluster approach. The assumption of independent bonding allows the contribution of cluster electrons to be calculated directly from their wave functions, without the use of shielding factors. Molecular rather than atomic wave functions are employed. Good agreement with experiment is obtained.

High-resolution x-ray photoelectron spectra of the total valence bands of crystalline and amorphous silicon and germanium are reported. For the crystals, the spectra yield results that are strikingly similar to current theoretical calculations of the electron density of states, $\rho \mathrm{}\left(E\right)\mathrm{}$. Amorphous Si and Ge exhibit definite band structures that are similar to one another but markedly different from the crystalline results. They agree very well with the theoretical model of Joannopoulos and Cohen.

By measuring the time of flight of heat pulses using superconducting tunnel junctions, we have obtained the frequency dependence of the energy velocity of acoustic waves in indium antimonide. This yields, with good accuracy, the dispersion relations for long wavelengths.

The contribution to the diamagnetism of cadmium coming from the region around the vertical edges of the Brillouin zone has been calculated. The calculation consisted of the application of Fukuyama's formula to the Bennett-Falicov model. The results explain the types and magnitudes of the structures observed by Svechkarev and Kuzmicheva in the susceptibility curves of Cd-Mg and Cd-Hg alloys.

Measurement of the static dielectric constant of solid methane crystals grown at high pressures show several anomalous regions. One set is associated with the well-known solid-solid phase transitions, while another is suggestive of ferroelectric behavior.

The photoabsorption coefficient in crystalline Si is computed in the 100-eV region ($L_{\mathrm{II}},L_{\mathrm{III}}$) on the basis of core excitons, using an adaptation of the effective-mass theory. The line shape is in good agreement with experiment, and, using experimental evidence from the phosphorus impurity in Si as to the central-cell correction, we find the absolute value to be compatible with experiment.

The first high-resolution valence-band x-ray photoemission spectra for Ge, GaAs, and ZnSe are compared with pseudopotential density-of-states calculations. The general agreement between the experimental and theoretical results is quite good. For ZnSe the photoemission spectrum shows the $\mathrm{Zn} 3d$ states to be higher in energy than the lowest valence-band $s$ state. In order to obtain this ordering of states in the theoretical calculation, a pseudopotential with an explicit energy dependence is required.

Anomalies in the shapes of angular distributions with respect to predictions of the distorted-wave Born approximation for several weak transitions in the reactions ${}_{}{}^{172}{}_{}{}^{}\mathrm{Yb}\mathrm{}(p,d)\mathrm{}$ and ${}_{}{}^{186}{}_{}{}^{}\mathrm{W}\mathrm{}(p,d)\mathrm{}$ are interpreted as resulting from inelastic excitations in the entrance and exit channels. These anomalies are shown to be reproduced when the reactions are treated within the coupled-channel Born approximation.

Inelastic electron scattering from the giant dipole resonance region in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ was measured. In addition to the usual dipole resonance we have found new resonances at 14.0 MeV and around 28 MeV. The spins and parities and transition strengths of these states are discussed.