We derive indentities that express spin-spin and orbit-orbit interactions in terms of two-electron spin-orbit matrix elements. They can reduce, in effect, any study of the two-electron Breit-Pauli Hamiltonian for atoms or molecules to one of determining the spin-orbit integrals, thereby considerably unifying and simplifying the whole analysis.

$K$ x-ray spectra of Ca and V as produced by 15-MeV ${\mathrm{O}}^{4+}$ ion bombardment are compared with 6-MeV proton-induced spectra. The $K\alpha$ and $K\beta$ lines from the ${\mathrm{O}}^{4+}$ bombardment are found to be shifted approximately 54 and 157 eV, respectively, relative to the proton-induced spectra. Hartree-Fock-Slater calculations show that the observed shifts are on the order of those expected from atoms with two or three additional innershell vacancies. We argue that it is unlikely that the known low-energy ion-atom interactions could be responsible for such inner-shell ionization configurations.

We have observed anti-Stokes Raman scattering from metastable deuterium atoms. The results obtained are in good agreement with theoretical calculations.

The symmetry-adapted pair-correlation energy of diatomic helium was evaluated for five internuclear separations near the potential minimum by means of localized orbitals obtained from transformation of a molecular Hartree-Fock wave function. An attractive potential depth of 12.0°K at $R=2.96\mathrm{}$ Å was obtained in agreement with the best experimental estimates, leading to the conclusion that the omitted electron correlation within the helium atom does not affect the interatomic correlation energy by more than about 10%. This result is in essential agreement with that obtained independently by Bertoncini and Wahl. The electron correlation contribution is divided into $\sigma$, $\pi$, and $\delta$ parts as well as into its atomic symmetry so as to elucidate the magnitude of the various contributions.

A five-configuration wave function computed by multiconfiguration self-consistent field techniques has yielded a well depth $\frac{\epsilon }{k}=10.48\mathrm{}$°K at $r_m=5.659\mathrm{}$ bohrs and a potential zero $\sigma =5.037\mathrm{}$ bohrs for the interaction of ground-state He atoms. Improvement of the basis set yields, at $R=5.60\mathrm{}$, a potential $U\left(R\right)=11.38\mathrm{}$°K. It is suggested that calculations in the vein of the present approximation should converge to a well depth of close to 12°K. The long-range behavior of our potential is unexpectedly close to that commonly accepted for He-He and may change by as much as 15% as the wave function, in its present approximation, is improved.

Similarity arguments are used to show that the dc electrical conductivity of a plasma is independent of the field, for a large enough field, even though the conductivity is completely determined by turbulence processes.

The effects of magnetic shear on unstable drift waves are studied in a straight $l=3\mathrm{}$ stellarator. Increasing the shear reduces the amplitude of the instability and also the cross-field diffusion coefficient.

The scaling laws for "anomalous" conductivity seen in a turbulent plasma are shown to depend on the type of electrostatic fluctuation spectrum present, which in turn depends on the relative drift velocity between ions and electrons.

Recent experimental charge-exchange studies of heavy ions have been utilized to modify the theory of Bohr and Lindhard for electron capture and loss by heavy ions passing through dense gases. New results are presented for the difference between the average ion charges obtained in dense and dilute gases, as well as for the residual ion excitation after charge-changing collisions. Implications are indicated for the measurement of radiative lifetimes of excited heavy ions.

Electric-dipole transition moments are calculated by a variational procedure which gives rigorous upper and lower bounds even though the exact wave functions are unknown. The method is applied to the lowest optical transition ($1s\sigma \to 2p\sigma$) of the hydrogen molecule ion, with satisfactory results.

Elastic differential scattering experiments have been performed on the system $p+\mathrm{He}$ at collision energies low enough to exclude inelastic channels. The experimental cross section is compared with the results of JWKB partial-wave calculations in which ab initio calculations of the interatomic potential have been employed. This comparison is seen to provide a very sensitive test of the accuracy of such potentials.

Theories of field ionization assume an atomically clean surface. Atom-probe experiments surprisingly revealed that the inert imaging gases are adsorbed at the field ion emitter. It is shown that this adsorption is due to a short-range field-induced dipole-dipole interaction. Adsorption at the apex of the protruding surface atom has considerable consequences for the mechanism of field ionization and field evaporation.

The temperature dependence of birefringence in the liquid crystal methoxybenzylidene-$n$-butylaniline has been obtained by measuring the birefringence of a thin sample placed between crossed polarizers. Measurements of transmitted laser light yield minima and maxima which can be related to the difference in refractive indices. A converging beam displays the orientation of the optic axis and is used in determining $\Delta n$. Wavelength dependence is measured in a similar way using white light and spectrograph.

If Tokamak toroidal discharges are operated with $q<\mathrm{}3\mathrm{}$, relaxation oscillations are observed to occur involving alternate contraction and expansion of the plasma. It is shown that the detailed properties determined for these oscillations on the Canberra experiment can be explained on the basis of the newly discovered trapped-particle pinch effect.

The phonon-induced $d-d$ coupling, calculated in tight-binding approximation, is shown to account for the order of magnitude of $T_c$ in transition metals. The model relates the coupling constant to the cohesive energy rather than to the melting temperature as proposed by Matthias.

Two-photon magnetoabsorption experiments are reported for the first time. From the splitting of the $2p$ excitons of ZnO in a magnetic field of 42 kG the hole masses and the $g$ values for the upper valence bands ${\Gamma }_9$ and ${\Gamma }_7$ are deduced.

Using resonance ruby-laser excitation, narrowing of the ruby $R_1$ fluorescence line to width 0.002 ${\mathrm{cm}}^{-1\mathrm{}}$ at 4.2°K is observed. Absence of spectral diffusion indicates that a short-range interaction rather than earlier postulated multipolar interactions is responsible for energy transfer in concentrated ruby.

The photoabsorption of LiF, LiCl, and LiBr has been investigated with high resolution at quantum energies from 60 to 230 eV using synchrotron radiation from an electron storage ring. It is found that the spectra can be understood largely in terms of transitions from the various core levels to the final-band density of states as obtained from recent band calculations. Features are found which may possibly be due to replication of the edge with the emission of one or more collective excitations.

In a field-normal microwave-frequency transmission experiment we observe strong resonant oscillatory bursts of microwave-field transmission through sheets of single-crystal copper. These bursts occur at field values appropriate to cyclotron resonance and its harmonics, but are not associated with Azbel'-Kaner cyclotron resonance. Instead we attribute the effect to a mechanism in which electrons propagating across the sample all arrive at the second surface with the same microwave phase, whenever the dc magnetic field satisfies the condition for cyclotron resonance.

It is demonstrated that the translational symmetry properties of the magnons and the lowest energy optical excitons in ${\mathrm{Cr}}_2$${\mathrm{O}}_3$ depend on the phases of the coefficients in the magnon or exciton quadratic boson Hamiltonian. This provides an explanation for recent observations that the magnons display two-sublattice symmetry and the excitons four-sublattice symmetry.