We have observed light-induced energy transfer in collisions of Eu atoms in three excited levels with Sr ground-state atoms and compared its spectra with the results of calculations. A four-photon parametric process in the transient Eu-Sr molecule was also observed.

The emission of a narrow line of electromagnetic radiation at the central plasma frequency, observed on several Tokamaks, is explained in terms of the scattering of enhanced plasma oscillations from thermal ion acoustic fluctuations. The emission and induced absorption rates calculated for the plasma fluctuation levels expected are considerable and the radiation is self-absorbed to an effective black-body level. The frequency, power, and polarization then predicted are in agreement with the experiment.

Theory and a particle-simulation code have been used to investigate resonance absorption of obliquely incident, $p$-polarized laser light by a magnetized inhomogeneous plasma. The absorption is increased (decreased) by the addition of the external magnetic field with the same (opposite) sign as the angle of incidence. The theoretical results from the two-dimensional particle simulations are in excellent agreement.

The magnetic behavior of bound shallow donors in CdS, a model $S=\frac{1}{2}$ amorphous antiferromagnet, has been measured by a Faraday rotation technique down to $T\sim 50$ mK. The susceptibility, $\chi$, and $\frac{d\chi }{\mathrm{dT}}$ as well increase monotonically with decreasing $T$ with no sign of an ordering transition even though the median exchange interaction of a spin is ∼7 K. The results agree with a hydrogeniclike exchange model which is solved in terms of exactly diagonalized weakly interacting clusters.

Spontaneous or self-polarization current peaks were observed in N${\mathrm{H}}_4$Cl and N${\mathrm{H}}_4$Br, when the samples were thermally cycled through their order-disorder phase transition. In N${\mathrm{H}}_4$Cl, but not N${\mathrm{H}}_4$Br, these peaks can be modulated by an externally applied electric field. It is expected that this difference is due to the ferromagneticlike order in N${\mathrm{H}}_4$Cl and the antiferromagneticlike order in N${\mathrm{H}}_4$Br.

Isotope-effect measurements on the binary Chevrel superconductor ${\mathrm{Mo}}_6$${\mathrm{Se}}_8$ are reported with either Mo or Se replaced by their isotopes. Within our uncertainty the isotope-effect exponent of $T_c\propto M^{-\beta }$ is equal in both cases (${\beta }_{\mathrm{Mo}}=0.27\mathrm{}\pm 0.04$, ${\beta }_{\mathrm{Se}}=0.27\mathrm{}\pm 0.05$). We concluded that only modes to which the six Mo and the eight Se atoms contribute about equally are determining $T_c$: These are acoustic translational modes of the ${\mathrm{Mo}}_6$${\mathrm{Se}}_8$ cluster and its internal optical modes, whereas torsional modes of the cluster must be of minor importance.

We present the first theoretical results on the anomalous field dependence of the Néel temperature for a system of loosely coupled classical Heisenberg chains with orthorhombic anisotropy for different directions of the applied magnetic field. The results compare favorably with the experimental phase diagrams of a series of selected $S=\frac{5}{2}$ compounds with varying degrees of one dimensionality and anisotropy.

The magnetic form factor of ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ is studied by taking account of the effects of core polarization and mesonic exchange currents. It is shown that the $M3\mathrm{}$ part of the singleparticle value is strongly canceled out by the core polarization.

The contribution to the nuclear charge density of the two-body pion-exchange charge operator is calculated for closed-shell nuclei from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ to ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ using density-dependent Hartree-Fock wave functions.

We observe strong structure in the excitation functions of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ backward-angle scattering. Angular distributions at the peaks of the elastic excitation function are of the form ${P_J}^2\left(cos\theta \right)$ [approximately $J=15\mathrm{}$ ($E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=23.3\mathrm{}$ MeV), $J=18\mathrm{}$ ($E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=26.0\mathrm{}$ MeV), and $J=18\mathrm{}$ ($E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=30.2\mathrm{}$ MeV)]. These results appear to be inconsistent with existing theoretical descriptions of anomalous backward-angle heavy-ion elastic scattering in this mass region.

Fission probabilities are presented for a series of Pu, Cm, and Cf nuclei with neutron numbers, $N$, in the range of 150-154. Results show that the fission thresholds are slowly varing with $N$ and $Z$ for $N=150-153\mathrm{}$ but there is a strong decrease in the threshold for $N=154\mathrm{}$. For ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ ($N=154\mathrm{}$) the results indicate broad, strong resonances at ∼ 5.0 and 5.4 MeV and suggest the breakup of the first axially asymmetric saddle into two barriers with large $\hslash \omega$.

The spectra of protons, deuterons, tritons, and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ observed from the bombardment of 140-MeV $\alpha$ particles on a number of nuclei exhibit broad peaks. The behavior of these peaks suggests that they result from the breakup of the incident $\alpha$ particle. The breakup yield accounts for about 10% of the total reaction cross section. It appears that this process can be described in terms of a simple projectile-breakup model, similar to that originally proposed by Serber for deuteron breakup.

We report the first experimental evidence for Coulomb-nuclear interference in the excitation of high-spin states by very heavy projectiles. The data are intepreted with use of a model described previously, and the feasibility of using this method to study the deformed nuclear surface is demonstrated.

Data on continuum electron capture and loss for bare and highly ionized ${\mathrm{C}}^{q+}$, ${\mathrm{O}}^{q+}$ ions traversing Ar at energies 1.6-2.8 MeV/A reveal striking disagreements with corresponding theories. We demonstrate a velocity-independent ($\sim Z^{2.2\pm 0.2}$) scaling for continuum capture by bare ions, a $Z$-independent velocity scaling, and an approximately $q$-independent ($q=6, 7, 8$) equality of continuum electron-capture and-loss cross sections at velocities corresponding to ∼2 MeV/A.

A quantum description of the transmitted field is given. In the bistable situation, the stationary Glauber quasi probability distribution has two peaks thereby producing a first-order phase transition. For small incident field the linewidth of the transmitted light is proportional to the atomic density and becomes very narrow as the field approaches some critical value from below. Crossing this value the spectrum splits discontinuously into a triplet (dynamical Stark shift) where the central peak is as high as twice the side-bands.

We have measured the rate of erosion of thin films of water ice at low temperatures by bombardment with MeV hydrogen, helium, carbon, and oxygen ions. The effective "sputtering coefficients" are orders of magnitude higher than those anticipated from conventional sputtering theories. For example, for helium at 1.5 MeV, ∼10 ${\mathrm{H}}_2$O molecules are removed for each incident ion. We believe that the erosion process is closely associated with atomic ejection following ionization in the region near the surface.

Deuteron magnetic resonance splittings and their temperature dependence from deuterated liquid-crystal compounds are analyzed in terms of molecular conformation and orientational order. Three order parameters are found to be necessary to explain the smectic-$C$ (${\mathrm{S}}_C$) spectra whereas only two are required for the nematic (N), ${\mathrm{S}}_A$ and ${\mathrm{S}}_B$ phases. The data are consistent with the concept that the preferred conformation of the molecule remains unchanged at the N-${\mathrm{S}}_C$, N-${\mathrm{S}}_A$, and ${\mathrm{S}}_A-{\mathrm{S}}_B$ phase transitions as well as throughout the temperature range of these phases.

We report some unusual observations on the NMR spectrum and the clustering rate of $o$-${\mathrm{H}}_2$ at low ortho concentration in solid ${\mathrm{H}}_2$ at temperatures between 25 mK and 2 K. Evidence points towards motional narrowing of the HD impurities, the proton signal of which is observed for $T<\mathrm{}0.15\mathrm{}$ K, and a hopping of $o$-${\mathrm{H}}_2$ from one pair configuration into another. Furthermore, there is an unexpected increase of the clustering rate of the other $o$-${\mathrm{H}}_2$ molecules as the temperature decreases below ∼0.1 K.

The phonon structure of the 2.67-eV indirect transition in GaP has been resolved in a transverse electroabsorption measurement. The transition is shown to be from ${\Gamma }_{15}$ to $L_1$, contrary to previous assignments.

A simple generalized time-dependent Ginzburg-Landau equation valid for dirty superconductors in the vicinity of $T_c$ is derived. For thin homogeneous filaments it exhibits oscillatory phase-slip solutions below and above the critical depairing current. The results are compared with $I-V$ curves observed in whiskers and microbridges.