We present the first observation and interpretation of an interference effect in the infrared absorption spectrum of HD-rare-gas mixtures. This effect, due to constructive or destructive interference between allowed and collision-induced dipoles during a collision, is referred to as "intracollisional interference." Is is manifested by the appearance of a narrow line at the $R_1\mathrm{}\left(1\right)\mathrm{}$ position which increases with rare-gas density. This interference has relevance to the determination of HD abundance in planetary atmospheres.

The acceleration and heating rates of plasma electrons observed in a toroidal device have demonstrated the existence of an asymptotic state in which the electrons are isotropically heated with a thermal velocity approximately equal to the drift velocity.

A radiation spectrum ranging from 300 MHz to 5 GHz is observed in low-density discharges in Alcator. At the lower end this spectrum is strongly peaked at a frequency corresponding to the ion plasma frequency. The emission occurs if the ratio of the drift velocity to the thermal speed of the electrons exceeds 0.45 for discharges in hydrogen or 0.2 in deuterium. The onset of the radiation correlates with the production of energetic ions.

We have measured the surface tension of liquid ${\mathrm{He}}^4$ for ($(T_{\lambda }-100\mathrm{} \mathrm{mK})<T<(T_{\lambda }+100\mathrm{} \mathrm{mK})$ mK) with a resolution of 1 × ${10}^{-5\mathrm{}}$ using a capacitive differential-capillary-rise technique. The results show a change in the slope of $\sigma \mathrm{}\left(T\right)\mathrm{}$ of 0.0226±0.001 erg ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{K}}^{-1\mathrm{}}$ centered below the bulk $T_{\lambda }$. A discussion of the critical behavior is given.

Using the molecular-dynamics technique, we describe the dynamical evolution of phase separation by spinodal decomposition for a Lennard-Jones fluid quenched to the unstable region. This is the first direct observation of the initial stages of spinodal decomposition.

Coherent inelastic neutron scattering in fully deuterated nematic $p$-azoxyanisole indicates, for momentum transfers $\overrightarrow{\mathrm{Q}}$ perpendicular to the director $\overrightarrow{\mathrm{n}}$, phononlike collective excitations having a dispersion with two maxima and one minimum within $0.9<~Q<~3.2$ ${\mathrm{\AA }}^{-1\mathrm{}}$.

We observe a new three-photon nonlinear photoelectric effect in glass with visible cw laser light using a method for measuring very low electron emission rates based on optical levitation of transparent particles. Electrons are pumped into the conduction band of glass by the absorption of two photons and subsequently ejected in a single-photon step.

Transient hole transport in $a$-Se below 180 K is shown to be a stochastic process. The transition from the well-defined high-temperature transport with Gaussian dispersion to the low-temperature stochastic transport is not paralleled by a change in the activation energy of the hole drift velocity.

The scattering of two plasmon excitations in an electron gas is considered using the Bohm-Pines formalism. Estimates of the attractive plasmon-plasmon interaction arising from the exchange of an electron-hole pair suggest that the binding of a plasmon pair may be observable in some metals and degenerate semiconductors.

The new decay rates of mesons which have been published within the last year are examined to determine their consistency with SU(3) symmetry, vector dominance, and the quark model. It is shown that despite an apparent overall trend of the new data to disagree with certain quark-model predictions by a factor of 3 or so, the consistency of the data with usual ideas of low-energy phenomenology is impressive. It would appear that the new data do not constitute a crisis for the "old" physics.

Results are presented on the three single-pion production reactions $\nu p\to {\mu }^{-}p{\pi }^{+}$, $\nu n\to {\mu }^{-}n{\pi }^{+}$, and $\nu n\to {\mu }^{-}p{\pi }^0$. Measurements were made from threshold to a neutrino energy of 1.5 GeV using the Argonne National Laboratory 12-ft bubble chamber filled with hydrogen and deuterium and exposed to a broad-band neutrino beam. In addition to a resonant isopin $T=\frac{3}{2}$ $\pi N$ amplitude, we find a large $T=\frac{1}{2}$ amplitude as predicted by Adler.

Very tightly bound, abnormally-high-density states of nuclei, suggested as a possibility by Bodmer and by Lee and Wick, have been searched for as an anomalous isotope of radon. This was done by looking for high-energy $\gamma$ rays following thermal-neutron capture. The limit that may be set for the atomic concentration of such nuclides on Earth is ∼${10}^{-29\mathrm{}}$ atom of Si.

Significant Li $K$ excitation is observed in ${\mathrm{Li}}^{+}$ + He collisions at incident energies as low as 6 keV. To interpret the results a multistep process is proposed including two-electron excitation in the quasi molecule formed during the collision. The importance of this process is discussed for heavier collision systems.

A new effect is demonstrated in which a laser pulse can be made to induce a Kerr effect only at Raman-shifted frequencies. This permitted the observation of a Raman spectrum with a single dye-laser pulse. The pulse power required is a small fraction of that required to produce stimulated instabilities. The spectral information emerges in a coherent beam, phase matching is not necessary, and spectra can be obtained at any scattering angle.

Finite-bandwidth effects are investigated by using the random phase approximation. The conditions of validity are checked by solving exactly a particular model. It is found that a finite coherence length for the pump wave can favor the existence of absolute instability.

The role of the relativistic electron-mass variation in the evolution of large-amplitude electromagnetic waves near cutoff and in the generation of plasma waves by linear mode conversion is investigated. Shock formation and subsequent wave breaking along the electric field of the wave will enhance the absorption of the wave by the plasma.

We analyze the conditions for observing interference effects in transition radiation at optical frequencies produced by ion clusters of considerably smaller size than the wavelength of the emitted radiation. We consider the possibility of using these effects in the study of the clusters' structure and alignment when they traverse solid films. Numerical results are obtained for ${\mathrm{H}}_2^{+}$ incident on aluminum.

We describe superconducting-quantum-interference-device susceptibility measurements on several dilute natural and monoisotopic $\mathrm{Au}\mathrm{Yb}$ alloys down to 7 mK. Whereas $\mathrm{Au}{}_{}{}^{174}{}_{}{}^{}\mathrm{Yb}$ obeys a Curie law in the whole range of temperature, a very unusual case of a Van Vleck-like behavior due to an electronuclear singlet ground state is reported for $\mathrm{Au}{}_{}{}^{171}{}_{}{}^{}\mathrm{Yb}$.

Using Green's functions of electrons scattered at an impurity site, I derive expressions for the energy $\delta U$ solely in terms of the electronic scattering cross section. My formulas can correlate the excess specific heat of dilute alloys with their resistivity. Formulas are derived for nontrivial scattering mechanisms illustrated by three well-known models, all capable of exhibiting the anomalous scattering known as the Kondo effect.

The first direct observation of electric monopole transitions in solids is reported for tetracyanoquinodimethane using an inelastic electron scattering experiment. Good agreement is obtained with a semiempirical self-consistent molecular-orbital calculation which predicts dipole allowed transitions near 3 and 7 eV and optically forbidden monopole transitions near 5 eV. We find an anomalous momentum dependence in the shape of the first dipole transition, possible due to local field effects.