An electron-impact-ionization mechanism for ions is considered in which the projectile is first captured by the target to form a doubly excited resonant intermediate state. Subsequently, this state decays in two steps by double Auger emission. The effect upon the ionization cross section is large near the excitation threshold and effectively extends the apparent threshold for scattering excitation single Auger ionization to lower energies. A detailed calculation of the ionization cross section and rate coefficient is presented for ${\mathrm{Fe}}^{15+}$ targets.

We have studied the transition from laminar to Taylor vortex flow between concentric cylinders with the inner cylinder accelerating very slowly. The apparatus employs a novel visualization system allowing a time-series representation of all the vortices in the flow to be obtained at a given instant. We find that unless a quantization condition is satisfied, the flow exhibits stochastic, time-dependent effects over a significant range of Reynolds numbers.

Results are presented for the atomic-field bremsstrahlung photon spectrum at 90° from the bombardment of atoms of neon, argon, krypton, and xenon by 6-10-keV electrons. The experimental data are found to agree well with the theoretical calculations of Pratt et al. over the photon energy range from 4 keV to the end point of the spectrum.

We report measurements of the tilt angle $\psi$ near the second-order $\mathrm{Sm}A-\mathrm{S}\mathrm{m}C$ transition in azoxy-4,4′-di-undecyl-$\alpha$-methylcinnamate. Data analysis shows that this transition, which belongs to the same universality class as ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, has, in the absence of a constraining field, a critical exponent $\beta =0.36\mathrm{}\pm 0.005$.

The ratio between the cross sections for single-electron capture by highly charged ions colliding with atomic and molecular hydrogen has been investigated within the framework of the Bohr-Lindhard theory. It is shown that $\frac{\sigma \left({\mathrm{H}}_2\right)}{\sigma \left(\mathrm{H}\right)}$ can be represented as a universal function of the inherent scaling parameter over a wide range of ion energy and charge states. Generally, the ratio is different from the often-assumed value of 2.

The configuration-space Hamiltonian for a many-electron atom is derived clearing up some of the ambiguities concerning the projection operators which must occur in this Hamiltonian. In the process, numerical calculations which have been previously performed are justified. The elementary two-electron interaction in the presence of many other electrons is also discussed.

The asymptotic solution of light scattering from a perfectly conducting circular cylinder is derived using the Watson transformation method first applied by Franz. It is clearly demonstrated that the scattered pattern is a superposition of a reflected wave and radiation from two creeping waves propagating around the cylinder in opposite directions. An He-Ne laser was used as a light source with $\overrightarrow{\mathrm{H}}$ field parallel to the axis of an aluminum-coated quartz fiber at normal incidence. The positions of intensity maxima and minima of the scattered light predicted by the Franz theory were not fully in agreement with experiment. We found it necessary to consider the phase change of the reflected wave in order to obtain satisfactory agreement.

A method is described which converts the dense distribution of pole singularities given by a discrete representation of a Green's function or resolvent operator into an approximation to the smooth function defined by the continuum limit of such a representation. The method uses a finite-element approximation to the pole-strength distribution function, equivalent to the width function in a scattering problem. Three distinct applications of this method are provided by a model scattering problem, making use of Feshbach resonance theory, the Schwinger variational principle, and the theory of the Fredholm determinant, respectively.

By explicit calculation on the one-dimensional Dirac equation, we exhibit an ambiguity in defining the relativistic $\delta$-function potential.

Measurements of the directional correlations between $K$ x rays following internal conversion and $\gamma$ rays in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ have been made. For the cascades in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ the correlation coefficients are $A_{22}(K{\alpha }_1-131\mathrm{}\gamma )=-0.032\mathrm{}\pm 0.007$, $A_{44}(K{\alpha }_1-131\mathrm{}\gamma )=+0.014\mathrm{}\pm 0.008$, $A_{22}(K{\alpha }_2-131\mathrm{}\gamma )=-0.017\mathrm{}\pm 0.007$, and $A_{44}(K{\alpha }_2-131\mathrm{}\gamma )=0.012\mathrm{}\pm 0.007$. For the cascades in ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ the correlation coefficients are $A_{22}(K{\alpha }_1-133\mathrm{}\gamma )=-0.037\mathrm{}\pm 0.012$, $A_{44}(K{\alpha }_1-133\mathrm{}\gamma )=0.022\mathrm{}\pm 0.017$, $A_{22}(K{\alpha }_2-133\mathrm{}\gamma )=-0.038\mathrm{}\pm 0.017$, and $A_{44}(K{\alpha }_2-133\mathrm{}\gamma )=0.037\mathrm{}\pm 0.029$. The anisotropic correlations in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ verify the existence of the effect and serve as a test case for x rays following magnetic-dipole internal conversion. The measurements in ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ establish the second known case of this phenomenon and in addition were made with better energy resolution. This case involves several mixed nuclear transitions which result in 38% of the x rays following electric-quadrupole internal-conversion processes.

The hyperfine structure of the rubidium atom in the excited $6{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, $7{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, and $8{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ states has been studied using the relativistic many-body perturbation procedure. The contributions from the different mechanisms, namely, the direct, the exchange core polarization (ECP), and the correlation effect are evaluated relativistically for each excited state. The contributions from these effects add up to net totals of 820 ± 16, 320 ± 6, and 156 ± 3 MHz, respectively, for the $6{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, $7{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, and $8{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ multiplet excited states, in excellent agreement with the experimental values of 809.1 (5.0), 318.1 (3.2), and 159.2 (1.5) MHz, respectively, similar to the situation for the ground $5{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ state found in an earlier investigation. The contribution from the ECP effect as compared to direct remains constant at about 16% as we go from the ground to the higher excited states. The correlation contribution, however, decreases dramatically as a ratio of the direct, from 32% in the ground state to 18, 14, and only 9%, respectively, in the excited multiplet states $6{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, $7{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, and $8{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$. The physical reasons for the observed trends in the contribution from the ECP and correlation effects is discussed, as is the implications of our results for the expected trends for these contributions in related systems like the ground and excited states of other alkali-metal atoms and noble-metal atoms, and the Knight shifts in nuclear magnetic resonance experiments on alkali metals.

Considering the Na atom as an example, an approximation to the electron number density is constructed from H-like wave functions. Using this electron density, the Thomas-Fermi-Dirac (TFD) and Thomas-Fermi-Dirac-Weizsäcker (TFDW) energy-density functionals are optimized with respect to the $Z$ in the wave functions. The energy values obtained are compared with the energy values of Wang and Parr, who recently have attempted to introduce the shell structure into statistical models for neutral atoms.

We have measured the dependence of the Sr $K$-shell-ionization probability on the projectile energy in the vicinity of the $d$-wave iosobaric analog resonance at 5060 keV in the reaction ${}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}\mathrm{}(p,p)\mathrm{}{}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}$. The variation of the ionization probability with projectile enegy is interpreted in terms of a phase shift between the incoming and outgoing atomic ionization amplitudes due to the nuclear time delay.

Auger-electron emission from 400keV carbon ions excited in single gas collisions with C${\mathrm{H}}_4$, Ne, and Ar has been investigated. Prompt and time-delayed projectile electron-emission spectra have been measured, and spectroscopic assignments are given. Absolute inner-shell vacancy-production cross sections and relative line intensities deduced from the prompt and time-delayed spectra for excited carbon ions have been compared as a function of exciter gases. An enhanced probability for electron excitation into high-spin states in carbon is found. Especially for the collision system ${\mathrm{C}}^{+}$→Ne, a striking population of the $1s2s2p{}_{}{}^4{}_{}{}^{}P_{}^o{}_{}{}^{}$ quartet state relative to the berylliumlike quintet and boronlike sextet states is observed. It is assumed that this is accounted for by cascade-feeding mechanisms. In particular, cascades from Rydberg levels feeding the $\mathrm{C}\mathrm{IV} 1s2s2p{}_{}{}^4{}_{}{}^{}P_{}^o{}_{}{}^{}$, $\mathrm{C}\mathrm{III} 1s2s2p^2{}_{}{}^5{}_{}{}^{}P$, and $\mathrm{C}\mathrm{II} 1s2s2p^3{}_{}{}^6{}_{}{}^{}S_{}^o{}_{}{}^{}$ high-spin states are discussed. Finally, wavelengths associated with electric dipole ($E1\mathrm{}$) transitions among quintet terms in C III and sextet terms in C II are predicted using $\mathrm{ab}$ initio methods.

Experimentally measured single-electron-transfer cross sections are presented for bare nuclei and one-electron ions of C, N, O, and F following collisions with a He-gas target in the energy range from ∼0.5-2.5 MeV / amu. Excellent agreement is found between the $K$-shell ionization cross sections (electron loss by one-electron ions) and a theoretical plane-wave-Born-approximation calculation without inclusion of Coulomb-deflection and binding-energy corrections. Comparisons are also made between the capture cross sections (electron gain) and previously measured total projectile x-ray cross sections. The ratio of the x-ray cross section to the total capture cross section is compared to the same ratio found through a Brinkman-Kramers (BK) calculation. The results of the comparison show that the single normalization constant for the capture to each state, which was used in the theoretical analysis of the x-ray cross section, is inadequate. In particular, the results show that the BK calculation underestimates the capture of the electron to the $1s \mathrm{and} 2s$ states as compared to the higher, x-ray-emitting states. The total capture cross sections are also given as a function of $\frac{E}{M}$ (MeV / amu). For a given velocity the capture is dependent only upon the charge state of the incident ion. Also, the similar velocity dependence with average ratios of 1:0.68:0.44 for the charge-changing processes $q\to q-1\mathrm{}(q=8,7,\mathrm{and} 6)$ correspond to a $q^3$ dependence for the total cross section.

Absolute (i.e., unnormalized) total cross sections for the scattering of electrons by lithium atoms between 2 and 10 eV have been measured, using the atomic-recoil technique in the scattering-out mode. In this energy range, elastic scattering and impact excitation of the $2P$ state are the dominant processes. The results best fit the sum of the modified polarized-orbitals elastic scattering cross-section calculations of Bhatia, Temkin, Silver, and Sullivan [Phys. Rev. A 18, 1935 (1978)], and the close-coupling impact-excitation cross-section results of Burke and Taylor [J. Phys. B 2, 869 (1969)]. Agreement over the entire energy range is at the 10% level or better.

Two proposals have recently been made for improving the convergence of complex-coordinate calculations of electron-atom scattering resonances. The first is that complex (Siegert-type) functions be added to the usual basis of real functions, and the second is that bound-state basis functions not be rotated to the complex plane. In this paper we present calculations which test these suggestions for the lowest $e-{\mathrm{He}}^{+}$ resonance, comparing the results with previous studies. The stabilization length criterion is employed to assess the convergence and stability of the variational energies. We conclude that neither of these suggestions satisfactorily removes the difficulties associated with complex-coordinate calculations of resonance lifetimes.