The application of the macroscopic Maxwell equations to the resonant interaction of electromagnetic radiation and dielectric crystals consisting of molecules coupled via retarded dipole fields is investigated. The macroscopic fields are defined by space averaging over volume elements of linear dimensions $\Delta$ satisfying $a\ll \Delta \ll \lambda$, where $a$ is the intermolecular separation and $\lambda$ the wavelength in vacuo. The essential point of our method is the direct derivation from the microscopic equations of a constitutive relation for a finite dielectric, taking proper account of the radiation reaction terms and avoiding the use of an expansion in powers of the molecular polarizability. The results lead to a simple interpretation of the expressions for the internal fields derived by Vlieger along similar lines, and verify the validity of the standard equations of dispersion theory to all points inside the medium a distance $\Delta$ away from the surface. The transmission and scattering of radiation at or near a molecular resonance by media of over-all extent small and large compared to the wavelength are discussed for sphere and slab geometries, and the effective natural linewidths are calculated. The limits of validity of the constitutive relation are discussed, and the existence of frequency regions where the macroscopic description breaks down due to the appearance of large spatial variations in the dipole moments is pointed out. As an example of such "antiresonant" behavior and of the role played by the higher-order radiation-damping terms, the scattering of light from two interacting molecules is treated in detail. In the absence of sufficiently strong dissipative damping, the occurrence of antiresonance is predicted to be a general phenomenon giving rise to large oscillations in the scattering cross section even in the presence of spatial dispersion in a narrow region around the frequency where the expression for the macroscopic index of refraction diverges.

Emission of $K\alpha$ x rays from foil-excited sulphur beams at 40, 50, and 55 MeV has been observed. Lifetimes of the $\mathrm{}\left(1s2p\right)\mathrm{}{}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ state in helium-like and the $\mathrm{}\left(1s2s2p\right)\mathrm{}{}_{}{}^4{}_{}{}^{}P_{\frac{5}{2}}^{}{}_{}{}^{}$ state in lithium-like sulphur, which decay partially by magnetic-quadrupole transitions, have been determined. The energies of several transitions to the ground state in two- and three-electron sulphur ions have been determined by using a Doppler-tuned spectrometer and observing the beam both downstream and close to the exciting foil. It is pointed out that the identification of lines in the prompt spectrum of such highly ionized systems in terms of configuration-averaged satellites is inappropriate.

Measurements and calculations have been made of elastic scattering and electron detachment in collisions of ${\mathrm{H}}^{-}$ and ${\mathrm{D}}^{-}$ with He at energies of 5-120 eV. The measurements show no other inelastic processes occurring in this energy range. The mechanism responsible for electron detachment is assumed to be the crossing of the ${\mathrm{H}}^{-}$ bound state with the continuum of free states; the bound state is then assigned a complex energy. The measured elastic scattering differential cross section shows no structure except at $E\theta \sim 200$ eV deg, where there is a region of downward curvature in the graph of $log\sigma$ vs $\theta$. This is interpreted as the threshold angle for electron detachment, and it is directly related to the crossing point. By empirically fitting the experimental differential cross section, the general features of the complex potential were obtained. By using the resulting potentials, the total detachment cross section was calculated and compared to the experimental results of Bailey, May, and Muschlitz. Only fair agreement is found at low energies, and poor agreement at higher energies (>100 eV). The theory predicts an isotope effect in the elastic differential cross section, and this effect provides a test of the theory. A careful series of experiments at 20 eV displayed the effect. A preliminary measurement of the electron energy spectrum was also made.

Calculated $N$-shell Auger and radiative transition rates, yields, and level widths for $38\le Z\le 103$ were reported. To calculate the $N_{6,7\mathrm{}}$ transition rates it was necessary to find formal expressions in $\mathrm{LS}$ coupling for the Auger transition rate with initial $f$ holes. In so doing it was found that some expressions previously given for Auger transition rates involving initial $f$ holes were in error. The corrected expressions are presented herein. Because there exist no data on $N$-shell fluorescence yields, all comparisons with experiment are comparisons of level widths obtained in most instances from x-ray linewidth measurements. For $Z\le 57$ the calculated values are in reasonable agreement with experiment. However, when the $4f$ shell begins to be filled the calculated $N$-shell level widths appear to be significantly larger than the experimental level widths. Some of the discrepancy can be attributed to the sensitivity to Auger-electron energy of the $\mathrm{}\left(4l\right)\mathrm{}-\left(4\mathrm{}{l}^{\prime }\right)\left(4f\right)\mathrm{}$ super-Coster-Kronig-process.

Recent calculations of the ground-state energy of a system of four hydrogen atoms are reviewed from the point of view of discerning the short-range interaction potential between two hydrogen molecules. Consistency amongst the results of these calculations suggests that the potential for intermolecular separations in the region 1-2.5 ÅA can now be specified to about 10% with considerable confidence. Analytic fits to spherical averages of these results are presented. For calculations of properties of high-density solid molecular hydrogen, the bare pair potential may thus be regarded as well determined. The role of multicenter terms can then be examined; as for example, recent reported work seems to indicate that pairwise additivity is not altogether valid in practice.

The polarizations of the Balmer-$\alpha$ and -$\beta$ lines produced by dissociative collisions of ${\mathrm{H}}_2^{+}$ have been measured at energies from 0.1 to 10 keV for a helium target and from 0.1 to 3 keV for argon and krypton targets. The Balmer-α line exhibits almost zero polarization in all these experiments. The Balmer-$\beta$ line, however, has a maximum polarization near 13% for the helium target and lower maxima, 6.0% and 2.5%, for argon and krypton targets. The relationship of these results to selective excitation of the ${\mathrm{H}}_2^{+}$ molecule and to the angular distributions of the dissociation products is discussed.

A broad, prominent emission blend is observed between 15 and 22 Å from a plasma produced in a $\theta$-pinch deuterium discharge seeded with neon. The occurrence of this feature is associated with radiative-Auger-transition channels in various intermediate ion species, following the creation of short-lived $1s$-orbit vacancies by the dielectronic capture of free electrons. The calculated blended spectrum from several stages of ionization agrees with the measured contour. A similar feature is detected near 27 Å with oxygen seeding. The measured intensities and shapes indicate that $2{}_{}{}^1{}_{}{}^{}S\to 1{}_{}{}^1{}_{}{}^{}S$ two-photon spontaneous emission in heliumlike ions is negligible for existing plasma conditions.

The atomic independent-particle model of Green, Sellin, and Zachor (GSZ) is used to obtain potentials for electrons in ions of light elements ($Z\le 18$). The two parameters of such potentials are obtained by the ab initio procedure of Bass, Green, and Wood (BGW). Here the expectation of the exact Hamiltonian with respect to a Slater determined of one-electron wave functions corresponding to GSZ potentials is minimized. Total energies determined by this modified Hartree-Fock procedure are found to be in excellent agreement with Hartree-Fock values (usually within a hundred parts per million). Potential parameters obtained in this way are found to be strongly dependent on both the atomic number and the number of electrons in the ion. Several other simple analytic potentials are treated in a similar way and it is found that the two-parameter GSZ and Gaspar potentials yield energies substantially lower than one-parameter potentials of the forms used earlier by Bohr and Tietz.

Intensity-dependent ionization potentials for atomic hydrogen and helium in intense laser beams are computed using a theory published earlier. The transformation that yields intensity-dependent potentials is identical to one proposed by Kramers in 1948. Results are given in terms of a parameter that depends on both intensity and frequency of the incident radiation.

New structures detected in the electroionization spectrum of ${\mathrm{O}}_2$ are explained as $3l\sigma$ Rydberg states belonging to the series converging to the recently reported ∼24-eV ${}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ state of ${\mathrm{O}}_2^{+}$. Some ${\mathrm{O}}_2^{-}$ resonances related to these Rydberg states are observed with an electronic affinity of ∼0.5 eV. Numerous other structures, also appearing from 12.06 to 18 eV, originate from direct ionization and unresolved vibration of autoionizing states.

A general analysis of polarization effects, resulting from exchange collisions between electrons and two-electron atoms, is given using density-matrix techniques. The formalism is presented in some detail. In particular, collisions on spin-1 atoms are discussed. General equations are derived which relate the quantities, characterizing the polarization state of the final beam, to their counterparts before scattering. Both sets of quantities are connected by functions of the scattering amplitudes. Thus, from these general equations we can read off what information can be extracted from experiments with particles in any given initial polarization state. Furthermore, some of the obtained expressions may be useful in discussions of other reactions, for example, processes in which spin-orbit and tensor interactions are important.

Total charge-exchange cross sections have been measured for ${\mathrm{Ne}}^{+}$ and ${\mathrm{Ar}}^{+}$ incident on Cs vapor. Ion beam energies for ${\mathrm{Ne}}^{+}$ incident on Cs were in the energy range 1.72-40.2 keV. The cross section ${\sigma }_{+0\mathrm{}}$ for the incident ${\mathrm{Ne}}^{+}$ ions has the almost constant value of (540 ± 60) × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ in the energy range 1.72-7.0 keV. The cross section increases from 7 to 20 keV, reaching another plateau of (1010 ± 70) × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ in the energy range 20-40.2 keV. Ion beam energies for the ${\mathrm{Ar}}^{+}$ ions incident on Cs were in the energy range 1.44-28.7 keV. The cross section ${\sigma }_{+0\mathrm{}}$ is (710 ± 63) × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ at 1.44 keV. The cross section increases between 1.44 and 8.6 keV, reaching a plateau of (1020 ± 90) × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ in the energy range 8.6-28.7 keV.

Absolute measurements are reported of the total cross section ${\sigma }_{10}$ for charge transfer of ${\mathrm{F}}^{+}$ in ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, He, Ne, and Ar in the energy range from 14 to 100 keV. The measured cross sections are in qualitative agreement with theory. However, it is observed that the slopes of the cross section versus velocity for velocities above the maximum in the cross sections differ for molecular and atomic targets used in this study.

Observations of photoabsorption in La, ${\mathrm{La}}_2$${\mathrm{O}}_3$, Ce, and Ce${\mathrm{O}}_2$ in the vicinity of the $3d$ edges are given. Calculations of relative absorption intensities for Ce are shown to correspond well with the experimental data.

The algebraic variational method has been applied to the scattering of electrons by hydrogen atoms at intermediate energies. The atom was represented by an eleven-state expansion, including exact $1s$, $2s$, $2p$, and $3d$ states plus seven pseudostates. The pseudochannels are allowed to be open. Results are presented for $1s-2s$ and $1s-2p$ excitations for energies between 10 and 12 eV, and for $1s-1s$ elastic scattering from 10 to 30 eV.

Absolute values of inner-shell ionization cross sections have been obtained by electron impact using Auger-electron spectroscopy with gaseous samples. Values of the $L_{2,3}$-shell cross sections of Si, P, S, Cl, and Ti and the $M_{4,5}$-shell cross sections of Br and Sn are reported for incident-electron energies between 500 and 2500 eV. The corrections due to a hole redistribution by Coster-Kronig transitions are discussed.

The cross sections for photoionization from the $2{}_{}{}^1{}_{}{}^{}S$, $2{}_{}{}^3{}_{}{}^{}S$, $2{}_{}{}^1{}_{}{}^{}P$, and $2{}_{}{}^3{}_{}{}^{}P$ excited states of helium are calculated for photoelectron energies below the $n=2\mathrm{}$ threshold of ${\mathrm{He}}^{+}$ using Hylleraas bound-state wave functions and $1s2s2p$ close-coupling final-state wave functions. The resonant structures associated with the lowest-lying ${}_{}{}^1{}_{}{}^{}S$, ${}_{}{}^1{}_{}{}^{}P$, ${}_{}{}^3{}_{}{}^{}P$, and ${}_{}{}^1{}_{}{}^{}D$ autoionizing states of helium are found to be characterized by large values of the line-profile parameter $q$. The cross sections and the photoelectron angular-distribution asymmetry parameters for the $P$ states are calculated for various polarization states of the target atom and the incident photon. Experiments which would lead to the separate determinations of the $S$ and $D$-wave partial photoionization cross sections are discussed.

Differential cross sections are calculated using the two-state and four-state impact-parameter treatments for $\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}-\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$ elastic and inelastic collisions in the keV-energy region. The cross sections, computed as a function of scattering angle, are compared with those evaluated from the Born-wave and unitarized-Born approximations. Interesting differences are observed.

The electron-impact excitation cross sections of the $A{}_{}{}^1{}_{}{}^{}\Pi$, $E{}_{}{}^1{}_{}{}^{}\Pi$, $B{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$, $C{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$, $D{}_{}{}^1{}_{}{}^{}\Delta$, $a{}_{}{}^3{}_{}{}^{}\Pi$, $c{}_{}{}^3{}_{}{}^{}\Pi$, $b{}_{}{}^3{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$, $j{}_{}{}^3{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$, $a^{\prime }{}_{}{}^3{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$, and $d{}_{}{}^3{}_{}{}^{}\Delta$ states of the CO molecule have been calculated for the incident electron energies over the range of threshold to 1000 eV for the singlet states and up to 100 eV for the triplet states by means of the Born approximation with Ochkur's and Rudge's modification for treating electron-exchange scattering. The wave functions of the various electronic states used in this calculation were determined by the self-consistent-field procedure with the Gaussian-type orbitals as basis functions. The calculated generalized oscillator strengths of the $A{}_{}{}^1{}_{}{}^{}\Pi$, $E{}_{}{}^1{}_{}{}^{}\Pi$, and $C{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ state are in reasonable agreement with the experimental values of Lassettre et al., but a larger discrepancy is found for the $B{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ state. The total cross sections calculated by this scheme show satisfactory agreement with experiment (30% at 300 eV) for the $A{}_{}{}^1{}_{}{}^{}\Pi$ state and are generally within the range of uncertainty of the experimental data for $a{}_{}{}^3{}_{}{}^{}\Pi$. For the $B{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ and $b{}_{}{}^3{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ states the theoretical cross sections differ very significantly from the experimental data of Skubenich which, however, are in serious disagreement with measurements reported from two other laboratories.

A one-dimensional model of three-charged-particle scattering is studied and used as a testing ground for the complex-rotation method for finding resonances. It is shown that the rotation method is very efficient in the accurate location of resonance poles.