The charge-state distributions of 373-, 444-, and 552-MeV krypton ions passing through carbon foils of different thicknesses were measured; they were found to agree within about one charge state with the existing semiempirical predictions. Measurements of equilibrium distributions produced by Cu, Ag, and Au foils showed differences of two to three charge states when compared to C-foil results. Evidence is also given that the distributions are not significantly modified when the angle of observation is different from 0°.

We have observed many resonances by electron spectrometry in the differential excitation functions of the states $3s$, $3s^{\prime }$, $3p^{\prime }$, $4s^{\prime }$, and $3d$ of neon in the autoionization region. These measurements are compared to the data obtained by other spectroscopic methods and their interpretation is discussed. For the main resonances, the energies and natural widths are determined. Moreover, their effective strengths and profile indices are presented for the various decay channels in comparison with the data obtained in the ionization channel.

Absolute $L$-shell x-ray production cross sections have been measured for thin targets of Pd, Ag, and Sn at 1-MeV increments for incident protons in the range from 3 to 12 MeV and in 5-MeV increments for oxygen ions in the range from 15 to 40 MeV. $L$-shell ionization cross sections are calculated from theoretical average $L$-shell fluorescence yields and then compared to both plane-wave Born-approximation (PWBA) and binary-encounter-approximation (BEA) theories. The data are found to be higher than the theoretical predictions except at the lowest projectile energies.

Differential and integral electron impact cross sections for elastic scattering and for the excitation of the $4p{}_{}{}^3{}_{}{}^{}P$, $4p{}_{}{}^1{}_{}{}^{}P$, $5s{}_{}{}^1{}_{}{}^{}S$, and $5p{}_{}{}^1{}_{}{}^{}P$ states of zinc have been determined for the first time at 40 eV impact energy. The measurements were normalized to the absolute scale by utilizing the optical $f$ value of the $4p{}_{}{}^1{}_{}{}^{}P$ transition. We find that the integral cross section for the $4p{}_{}{}^1{}_{}{}^{}P$ excitation is quite large (1.0 × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$) and exceeds that for elastic scattering (2.1 × ${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$) by a factor of nearly 5.

To avoid the shortcomings of conventional methods such as the symmetry dilemma and the subtraction of large numbers of roughly equal magnitude, a Green's-function method is extended to the study of hyperfine splitting in atoms and molecules. With this method the hyperfine coupling constants are calculated for the ground and excited states of the molecule by a self-consistent equation, starting from the Hartree-Fock level of a closed-shell system. In this approach the one-particle picture is retained, and it is possible to study the hyperfine problem from a different physical point of view. The theory is applied to the calculation of the ground-state and some excited-state hyperfine coupling constants of Li and C${\mathrm{H}}_3$. It is shown that those terms of the perturbation expansion which are essential to explain the constant of the atom are unessential in the case of the methyl radical and vice versa. This result is generalized. The computational effort to evaluate the coupling constants has been found to be very small.

A comprehensive study of the angular and energy distributions of electrons ejected in collisions of fast electrons and protons with He is presented. New experimental results for 300-keV, 1-MeV, and 5-MeV proton impact are reported along with theoretical results for 2-keV electron impact and 100-keV, 300-keV, 1-MeV, and 5-MeV proton impact. The theoretical results, based upon Born approximation with Hartree-Slater initial discrete and final continuum wave functions, show excellent agreement with experimental electron-impact results. Serious discrepancies are found between theory and experiment in the angular distribution of ejected electrons for forward angles for 100- and 300-keV proton impact; the discrepancies decrease markedly for 1-MeV proton impact and are absent for 5-MeV protons. The agreement between theory and experiment for intermediate and backward angles of electron ejection, on the other hand, is uniformly good for all proton impact energies. The reasons for this behavior in terms of a charge-exchange process to a continuum state contributing to electron ejection at forward angles is discussed, and the energy dependence of the data is shown to be consistent with this explanation.

An integral representation is developed for the scattering amplitude for ionization by charged particles in the Glauber approximation. Unlike previous results based on a series expansion in the momentum of the ejected electron, ${\overrightarrow{\mathrm{k}}}_e$, the present results are rigorously convergent for all physical values of ${\overrightarrow{\mathrm{k}}}_e$. Results calculated by this method agree with earlier results for ionization of atomic hydrogen by electron impact using Padé approximants to approximately sum the series. Total cross sections for the ionization of atomic hydrogen by proton impact are presented and compared to experimental data. This technique is applicable to the ionization of neutral atoms whose participating electron is represented by a hydrogenic wave function, and the remaining electrons are ignored.

The absorption coefficient for collision-induced absorption in a He-Ar mixture is calculated for frequencies between 67 and 733 ${\mathrm{cm}}^{-1\mathrm{}}$ in the 200-400 °K temperature range. Starting with a Lennard-Jones (6-12) interatomic potential derived from atomic-beam work, the absorption coefficient is computed for five different dipole-moment functions. The calculation is quantum mechanical, dynamically exact, and uses no adjustable parameters. The results are compared with the room-temperature experimental results as well as with previous theoretical work.

By applying many-body perturbation theory, the effects of electron correlations are included in the calculation for the photoionization cross section of the neutral sodium atom from threshold to 16 eV for the photoejected electron energy. The improvement of the lowest-order Hartree-Fock approximation for the cross section by the first-order and second-order correlation corrections is small. The discrepancy between the experiment and the calculations at the short-wavelength side of the minimum is still not understood.

The neoclassical theory of radiation predicts that the decay rate of an excited atomic state depends on the population density of the lower state. Experimental evidence is presented here which shows that in the case of ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ the decay rate is in agreement with the predictions of quantum electrodynamics and definitely in disagreement with the neoclassical theory.

The lifetimes of the ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ states of Ne, Ar, Kr, and Xe are calculated by considering the spin-dependent magnetic-quadrupole ($\mathrm{SM}2\mathrm{}$) radiative transition to the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ state as the decay mechanism. By expressing the $\mathrm{SM}2\mathrm{}$ operator as a contraction of the spin magnetic dipole and the electric dipole, the lifetime of the ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ state can be expressed very simply in terms of that of the ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ state. With the known lifetimes of the ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ state, the calculated lifetimes of the ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ states are 24.4, 55.9, 85.1, and 149.5 sec, respectively, for Ne, Ar, Kr, and Xe. The lifetime of the ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state is calculated by considering both the magnetic-dipole ($M1\mathrm{}$) transition to ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ and the electric-quadrupole ($E2\mathrm{}$) transition to ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ as the decay mechanism. The calculated lifetimes are 430, 44.9, 0.488, and 0.078 sec, respectively, for Ne, Ar, Kr, and Xe. These calculated lifetimes are above the lower limits of the experimental lifetimes measured by Van Dyck, Johnson, and Shugart.

We have studied the quadratic Stark effect on the hyperfine structure in the ground states of the alkali-metal atoms, lithium through cesium. In evaluating the leading perturbation terms, we have utilized two sets of first-order wave functions, corresponding respectively to perturbations of the atomic wave functions by the electric field and by the nuclear moment. The perturbed wave-functions were obtained by solving the appropriate differential equations in first-order perturbation theory. The theoretical results agree very well with the recent experimental data for the entire series of alkali-metal atoms. A discussion of the relation of our theoretical results to earlier ones in some of the alkali-metal atoms is also presented.

Three-photon absorption spectroscopy allows determination of the $\mathrm{nf}{}_{}{}^2{}_{}{}^{}F_{\frac{5}{2},\frac{7}{2}}^0{}_{}{}^{}$ energy levels of alkali metals ($\Delta L=+3\mathrm{}$). The $3d{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2},\frac{5}{2}}^{}{}_{}{}^{}$ levels of KI were selectively excited using a narrow-band dye laser. The $3d{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2},\frac{5}{2}}^{}{}_{}{}^{}\to \mathrm{nf}{}_{}{}^2{}_{}{}^{}F_{\frac{5}{2},\frac{7}{2}}^0{}_{}{}^{}$ absorption lines were observed in the background spectrum of another dye laser, and the $\mathrm{nf}{}_{}{}^2{}_{}{}^{}F_{\frac{5}{2},\frac{7}{2}}^0{}_{}{}^{}$ energy levels were deduced, from $n=10\mathrm{}$ to $n=14\mathrm{}$ inclusive, with an accuracy better than 0.1 ${\mathrm{cm}}^{-1\mathrm{}}$. Previously, an experiment was performed for the $7f{}_{}{}^2{}_{}{}^{}F_{\frac{5}{2},\frac{7}{2}}^0{}_{}{}^{}$ levels in order to verify the method. Shifts and systematic errors were entirely negligible. For all lines, the relative intensities of the absorbed doublet peaks are in good agreement with the estimates of the $4s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}\to 3d{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2},\frac{5}{2}}^{}{}_{}{}^{}$ probabilities.

Accurate quantum-mechanical calculations on the system hydrogen-antihydrogen ($\mathrm{H}\overline{\mathrm{H}}$) are presented. The energy is calculated using the Ritz variational principle, and is obtained as a function of the proton-antiproton distance in the Born-Oppenheimer approximation. It is everywhere lower and therefore more accurate than that recently calculated by Junker and Bardsley. In particular, the maximum in the interatomic interaction reported by these authors is not seen in this calculation. The cross section for rearrangement annihilation is calculated and found to be uniformly larger than that reported by Junker and Bardsley.

Numerical calculations for the tip region of the electron bremsstrahlung spectrum are reported for incident electron kinetic energies in the range from 50 keV to 1.84 MeV. The calculations are exact within the framework of a single electron in a screened central potential and are obtained by summing integrals resulting from a partial-wave expansion of the wave functions. Results are compared with previous theoretical calculations and with experiments. For low energies the screening correction to the spectrum is generally not small. We find that for high-$Z$ elements the discrepancies between theory and experiment reported by Starek, Aiginger, and Unfried are due to the use of inaccurate theoretical approximation. For low-$Z$ elements the discrepancy remains.

A detailed comparison is carried out between consistency contributions to the nuclear quadrupole antishielding factor for the ${\mathrm{Fe}}^{+3\mathrm{}}$ ion obtained by the linked-cluster many-body perturbation procedure, as well as a procedure employing perturbed wave functions used in conventional differential-equation procedures for studying antishielding factors. The agreement between results by the two procedures is found to be good, indicating that the procedure using perturbed wave functions is a viable one for studying consistency effects, at least for positive ions.

The formation and decay of ${\mathrm{Hg}}_2$ molecules in their ${}_{}{}^3{}_{}{}^{}1_u^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}0_u^{-}{}_{}{}^{}$ states, produced in Hg-Ar mixtures irradiated with 2537-Å Hg resonance radiation, has been investigated by the method of delayed coincidences. The mixtures which consisted of Hg vapor at a pressure of about 1 Torr and Ar at pressures of 45-720 Torr and which were contained in a quartz fluorescence cell, were excited with pulses of light, and the decay spectra of the 3350- and 4850-Å molecular fluorescent bands were studied in relation to Ar pressure. Analysis of the decays indicates that the effective cross sections for ${}_{}{}^3{}_{}{}^{}1_u^{}{}_{}{}^{}\leftrightarrow {}_{}{}^3{}_{}{}^{}0_u^{-}{}_{}{}^{}$ mixing, induced in ${\mathrm{Hg}}_2$-Ar collisions are of the same order as the ${\mathrm{Hg}}_2$-${\mathrm{N}}_2$ mixing cross sections, leading to the conclusion that the 4850-Å band is emitted mainly by ${}_{}{}^3{}_{}{}^{}0_u^{-}{}_{}{}^{}$ molecules in high vibrational states.