Through a variational calculation, the ground-state binding energy of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ trimer is computed using the ab initio potential of Bertoncini and Wahl. These results indicate a stable trimer bound by 0.3 °K.

The ionization of $K$-shell electrons by heavy particles is examined in the energy region where the projectile is moving faster than the orbiting electron. An explanation suggested for the rise of the experimental results above the Born approximation is the mechanism of "charge exchange to the continuum." An estimate of the effect shows reasonable agreement with experiment.

Magnetic hyperfine splittings of rotational levels in muonic deformed nuclei are calculated microscopically within the self-consistent cranking model, taking into account the finite extension of the nucleus. A previous oversight in the theory of the magnetic interaction between the muon and the nucleus is corrected. The splittings are found to be about 25% larger than the earlier estimates. These new values seem to remove the discrepancy between muonic and Mössbauer isomer shifts in the rare-earth region.

The oscillator strength for the ${}_{}{}^1{}_{}{}^{}S-{}_{}{}^1{}_{}{}^{}P_{}^o{}_{}{}^{}$ transition in atomic oxygen has been measured using resonance-absorption techniques. The metastable absorbing atoms were formed in a weak dc discharge at a pressure of a few Torr, and their concentration determined by absolute photometry of the auroral green line arising in the ${}_{}{}^1{}_{}{}^{}D-{}_{}{}^1{}_{}{}^{}\mathrm{S}$ transition. The light source for the emission line was a water-cooled hollow-cathode discharge operated in pure oxygen at a pressure of 0.25 Torr and a current of 70 mA; self-reversal was negligible. A pure Gaussian line profile was assumed to describe the shapes of the emission and absorption lines. Treating $f$ as a parameter and using measured values for emission and absorption temperatures and absorber concentration, a computer search was made to find that $f$ which gave the best fit of the absorption integrals to the experimental data. The experimental oscillator strength of 0.051 ± 0.018 compares satisfactorily with the theoretical estimate of 0.13 ± 0.06, but is at least 50% smaller than other experimental values reported.

Absolute transition probabilities are measured for 24 prominent Ge I and Ge II lines between 3200 and 6500 Å. Spectroscopic plasmas are generated by the shock heating of neon or argon containing (0.2-2.0)% Ge${\mathrm{H}}_4$ to temperatures 10 200-12 600° K at pressures of (6-32) × ${10}^6$ dyn ${\mathrm{cm}}^{-2\mathrm{}}$. To reduce possibilities for bias, the state of the light source and the integrated energy of emitted lines were determined redundantly. $A$ values were measured by methods inherently insensitive to possible temperature errors. Ionic transition probabilities [estimated accuracies (23-50%] are compared with central-field approximations and are tested for conformity with quantum-mechanical sum rules. Neutral germanium data [accuracies (30->50)%] are compared with other experimental results.

The measurements of Allen on autoionized line intensities of copper were carried out again with reference to the electron density $N_e$ of the plasma. The measurements here show a notable deviation of autoionizing-level populations relative to Boltzmann's law, but a much more severe disagreement for an adjacent nonautoionizing level. We encounter a paradoxical situation where Saha's law is assumed for the autoionizing levels when $N_e$ is small, following autoionization theory, but where a deviation from it is observed when $N_e$ is notable, i.e., in the range of low-current atmospheric arcs. Evaluation of the various usual contributions to the population variations cannot account for the observed curves. Other processes must be included in the calculation.

New Hund's rules are proposed for atoms for $\mathrm{jj}$ coupling. It is found that two distinct rules are needed depending on the relative values of $j_i$ and $l_i$ for interacting electrons.

We report a new experimental technique for testing the electrical neutrality of molecules. An alternating electric field applied to an acoustic cavity containing S${\mathrm{F}}_6$ gas will generate sound at the electric field frequency if the gas has a charge. With a suitably calibrated microphone in the cavity the sound pressure can be measured yielding an upper limit for the charge per molecule $\epsilon$. Dividing by the mass number of the molecule (146) yields an upper limit for an electron-proton charge difference. (This last result assumes that the electron-proton charge difference equals the neutron charge.) The results: $\left|\epsilon \right|\le 2\times {10}^{-19\mathrm{}}e$ and $\frac{\left|\epsilon \right|}{M}\le 1\times {10}^{-21\mathrm{}}e$, where $e$ is the magnitude of the electronic charge, are consistent with the fundamental belief of zero charge imbalance. The measurement is less affected by the presence of ions than other macroscopic neutrality measurements and has an estimated maximum sensitivity of $\left|\epsilon \right|\le {10}^{-22\mathrm{}}e$.

The hyperfine interactions in the $2{}_{}{}^2{}_{}{}^{}P$, $3{}_{}{}^2{}_{}{}^{}P$, and $4{}_{}{}^2{}_{}{}^{}P$ states of ${\mathrm{Li}}^7$ are studied, using the spin-optimized self-consistent-field (SO-SCF) and unrestricted Hartree-Fock methods. It is found that the use of a single $〈r^{-3\mathrm{}}〉$ parameter to describe all three hyperfine interactions is inadequate for all states considered, as has previously been found for the $2{}_{}{}^2{}_{}{}^{}P$ state. The experimental results for $3{}_{}{}^2{}_{}{}^{}P$ and $4{}_{}{}^2{}_{}{}^{}P$ states are reanalyzed and the following values are obtained: $3{}_{}{}^2{}_{}{}^{}P: a_{\mathrm{orb}}=2.58\mathrm{}\pm 0.05$ MHz, $a_{\mathrm{dip}}=-0.57\mathrm{}\pm 0.02$ MHz, $a_c=-2.98\mathrm{}\pm 0.06$ MHz; $4{}_{}{}^2{}_{}{}^{}P: a_{\mathrm{orb}}=1.10\mathrm{}\pm 0.03$ MHz, $a_{\mathrm{dip}}=-0.24\mathrm{}\pm 0.01$ MHz, $a_c=-1.27\mathrm{}\pm 0.03$ MHz. The lifetimes of the $2{}_{}{}^2{}_{}{}^{}P$ and $3{}_{}{}^2{}_{}{}^{}P$ states are calculated using the SO-SCF method, showing good agreement with experimental values for the $2{}_{}{}^2{}_{}{}^{}P$ state, but giving a lifetime for the $3{}_{}{}^2{}_{}{}^{}P$ state which is about 20% too long.

Spectra have been measured [using a crystal (LiF;200) spectrometer] of $L$ x rays produced by 2.0-MeV proton, 3.2-MeV $\alpha$-particle, and 30.0-MeV oxygen bombardment of thick tin targets. $L$ x-ray lines are observed in the $\alpha$-particle-produced spectrum from initial configurations with up to four additional $M$-shell electron vacancies. The energy resolution of 8 eV (full width at half-maximum) did not allow any detailed structure to be resolved in the oxygen bombardment; an almost continuous structure is observed from multiply ionized tin. The ratios of x-ray yields from $L+M$ vacancies to yields from $L$ vacancies are shown to have the correct order of magnitude for a simultaneous direct Coulomb ionization process for proton and $\alpha$-particle impact.

We derive an equation describing the electrocaloric effect in fluids, which differs from that predominantly employed in current theoretical studies of nonlinear optics. The consequent alterations in the predictions of nonlinear optical theory and in the interpretation of experimental observations are then described.

For the test case of 300-eV electrons incident on Hg the influence of the exchange of the incoming electron with the atomic electrons is studied. Four different approximations for the derivation of an exchange potential based on the free-electron-gas description are discussed. These approximate exchange potentials were employed in calculations of electron scattering factors. The comparison of those results with a rigorous Hartree—Fock (HF) treatment of the total scattering problem ($N+1\mathrm{}$ particles) shows that the exchange given by Kohn and Sham is too large, especially at large atomic distances. By Gombás's introduction of a cutoff at the radius of the Thomas—Fermi—Dirac atom, the long tail of the potential was avoided. While the truncated results of Gombás decrease the deviations significantly, a different treatment of the self-exchange as suggested by Lindgren and Rosen brings the best agreement with the HF calculation. The theoretical results show that precise relative measurements in the valleys of the different cross sections are an extremely sensitive tool for testing scattering theory.

An accurate differential ionization cross section for the ejection of zero-kinetic-energy electrons from He by fast charged particles is deduced by extrapolating the Born cross sections for discrete excitations, in the spirit of the quantum-defect theory. Recent electron-impact data by Grissom et al. for secondary electrons of almost zero kinetic energy are in excellent agreement with the theory. The electron-impact data by Peterson et al. for slow secondary electrons show trends consistent with the theory also. The proton-impact data by Rudd et al. are in better agreement with the theory than those by Stolterfoht.

Measurements for the differential scattering of protons by helium and argon as a function of scattering angle and impact energy are presented for the range 3-20 keV and 1°-5° laboratory angle. The measurements are of the sum of elastic, inelastic, and charge-changing collisions. Comparison is made with two classical calculations, one employing the Bohr screening length, the other employing separate screening lengths for each electronic shell. For argon, the data are in significantly better agreement with the calculation employing separate screening lengths for each electronic shell.

Cross sections for the production of x rays by protons have been determined at 1.00, 2.25, and 3.00 MeV. The $K\alpha$ production was measured for Ti, V, Fe, Ni, Cu, Ge, Rb, Zr, Ag, Sn, and Sb. The $L\alpha$ production was measured for Ce, Sm, Dy, Tm, W, Au, Pb, Bi, Th, and U. In addition, excitation functions were determined in 100-keV steps from 1.00 to 3.70 MeV for $K\alpha$ production in Ni, Ge, and Ag and for $L\alpha$ production in Sm, W, and Th. The results compare well with the predictions of the plane-wave Born approximation and the binary-encounter approximation.

A method for obtaining series solutions to nonrelativistic three-body problems is investigated; a calculation of the $1{}_{}{}^1{}_{}{}^{}S$ ground state of the helium atom is performed as a test, and results are compared with previous work.

The radiative decay of $K$-shell vacancies of argon, krypton, and xenon, and $L$-shell vacancies of krypton and xenon, has been observed with a Si(Li) x-ray detector for thin gas targets of these atoms excited by 1.5- to 5.0-MeV protons. X-ray yields were measured as a function of target thickness under single-collision conditions, and inner-shell ionization cross sections were determined using atomic fluorescence yields. The $L$-shell ionization cross sections obtained are in good agreement with theoretical calculations in the plane-wave Born approximation. The $K$-shell cross sections show good agreement with these calculations for the argon $K$ shell, but fall above the theoretical values for krypton and xenon, the discrepancy with theory increasing with increasing atomic number. The binary-encounter model was also compared to the experimental $K$-shell ionization cross sections, and for all gases the agreement is somewhat worse. $\frac{K\beta }{K\alpha }$ relative intensities for krypton and xenon were determined, and good agreement of these values with the results of experiments using other modes of excitation is shown.