In order to evaluate more accurately the nuclear electric-quadrupole moments of ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}$ and ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$ from recent atomic-beam hyperfine-structure (hfs) studies, the eigenvector of the atomic ground state is obtained from a three-configuration least-squares fit to all known low-lying even-parity atomic levels. Relativistic Dirac-Slater $〈r^{-3\mathrm{}}〉$ values are used in interpreting the hfs. The nuclear dipole moments deduced in this way from the dipole hfs are within 3% of the known values. The resulting quadrupole moments are 0.67(13) b and 0.61(12) b for ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}$ and ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$, respectively. Most of the quoted uncertainty arises from uncertainty in the Sternheimer shielding correction applied.

An excitation Hamiltonian is formulated by adding an operator $\hat{O}\hat{A}\hat{O}$ to the Fock operation whose eigenvalue differences represent excitations of electronic systems. $\hat{O}$ is an operator which projects onto the virtual space of the Fock operator and $\hat{A}$ is chosen so that one has a Koopmans theorem and a variational principle for these states. The formalism is then used to calculate excitation energies of atomic He, Li, Be, and Na.

The $\frac{L{\gamma }_1}{L{\beta }_1}$, $\frac{L\eta }{L{\beta }_1}$, $\frac{L_1}{L\alpha }$, and $\frac{L{\beta }_{2,15}}{L\alpha }$ radiative transition probabilities have been measured for 16 elements ranging in atomic numbers from ${}_{42}{}^{}{}_{}{}^{}\mathrm{Mo}$ to ${}_{62}{}^{}{}_{}{}^{}\mathrm{Sm}$. This was performed using an evacuated single-crystal spectrometer in conjunction with a flow proportional counter. The samples studied were pure metals in an amorphous state except for ${}_{56}{}^{}{}_{}{}^{}\mathrm{Ba}$, ${}_{59}{}^{}{}_{}{}^{}\mathrm{Pr}$, and ${}_{60}{}^{}{}_{}{}^{}\mathrm{Nd}$, where the oxides of these elements were used. CsCl and NaI samples were used to study the spectrum of ${}_{55}{}^{}{}_{}{}^{}\mathrm{Cs}$ and ${}_{53}{}^{}{}_{}{}^{}\mathrm{I}$, respectively. Ionization of the samples was produced by radiation from commercial ${}_{74}{}^{}{}_{}{}^{}\mathrm{W}$ and ${}_{24}{}^{}{}_{}{}^{}\mathrm{Cr}$ x-ray tubes. The corrected measured ratios are compared with the results of the theoretical calculations based on relativistic Hartree-Fock-Slater potential.

Using an electron transmission spectrometer the energetically lowest-lying Feshbach resonances in the molecular halogens ${\mathrm{F}}_2$, ${\mathrm{Cl}}_2$, ${\mathrm{Br}}_2$, and ${\mathrm{I}}_2$ are located. These resonances are associated with Rydberg states and have symmetry $\left(X{}_{}{}^2{}_{}{}^{}\Pi _g^{}{}_{}{}^{}\right){\left(ns\sigma \right)}^2\left[{}_{}{}^2{}_{}{}^{}\Pi _{\frac{1}{2},\frac{3}{2}}^{}{}_{}{}^{}\right]$, where $n=3,4,5, \mathrm{and} 6$ for ${\mathrm{F}}_2$, ${\mathrm{Cl}}_2$, ${\mathrm{Br}}_2$, and ${\mathrm{I}}_2$, respectively. The binding energy of the lowest pair of $\mathrm{ns}\sigma$ electrons to the ground-state positive ion core decreases monotonically as the size of the molecules increases from 4.45 ± 0.05 eV in fluorine to 3.57 ± 0.05 eV in iodine. A simple qualitative theoretical argument, based on an atomic model, satisfactorily describes the decrease in the binding energy.

The x-ray spectrum in the region from about 2 to 42 keV has been measured for 25-MeV iodine ions incident on thick and thin gold targets, 37.8-MeV gold ions incident on thick tin targets, and 23.9-MeV gold ions incident on thick gold targets. The spectra were obtained for several values of aluminum absorbers inserted between the target and detector. The broad band of x-ray emission lying in energy between about 6.5 and 9.5 keV observed by Mokler et al. is confirmed as is their suggestion that it arises from $M$ x rays from the quasiatom system of $Z\simeq 130$. A search for $L$ x rays from these systems was inconclusive.

Using a velocity-independent analysis of zero-field quantum beats in time-resolved decays of the $\mathrm{np}{}_{}{}^3{}_{}{}^{}P\mathrm{}(n=2-5\mathrm{})\mathrm{}$ terms of ${}_{}{}^{6,7}{}_{}{}^{}\mathrm{Li}$ II, we have obtained measurements of (a) the fine-structure separations $J=0\mathrm{}$ to $J=1\mathrm{}$ and $J=0\mathrm{}$ to $J=2\mathrm{}$, (b) the hyperfine contact terms, and (c) the dipole terms of the hyperfine interaction. Our accuracy is a few parts in ${10}^3$ for some of the constants. In some cases, the fine-structure constants are in significant disagreement with the calculations of Accad, Pekeris, and Schiff. The hyperfine constants for the $n=2\mathrm{}$ term are close to recent many-body calculations.

The rotational spectrum of DTO and HTO in the ground vibrational state has been measured with high-resolution microwave techniques in the 50-700-GHz region. We have measured and assigned 41 transitions of DTO. Analysis of these data yielded the following rotation and distortion parameters of the Watson formulation (in MHz): $\mathcal{A}=410\mathrm{}174.145\pm 0.078$, $\mathcal{B}=172\mathrm{}101.952\pm 0.045$, $\mathcal{C}=199\mathrm{}127.850\pm 0.045$, ${\Delta }_J=5.199034\mathrm{}\pm 0.003$, ${\Delta }_{J\mathrm{K}}=-15.50411\mathrm{}\pm 0.015$, ${\Delta }_K=180.31052\mathrm{}\pm 0.010$, ${\delta }_J=1.941256\mathrm{}\pm 0.0010$, ${\delta }_K=12.8893\mathrm{}\pm 0.012$. We measured 22 previously undetected transitions of HTO. Analysis of these, together with 26 lines already known, gave the following rotation and distortion parameters (in MHz): $\mathcal{A}=677\mathrm{}849.040\pm 0.170$, $\mathcal{B}=198\mathrm{}197.489\pm 0.128$, $\mathcal{C}=150\mathrm{}462.412\pm 0.128$, ${\Delta }_J=5.212023\mathrm{}\pm 0.003$, ${\Delta }_{\mathrm{JK}}=48.52276\mathrm{}\pm 0.02$, ${\Delta }_K=271.27533\mathrm{}\pm 0.06$, ${\delta }_J=1.414126\mathrm{}\pm 0.0005$, ${\delta }_K=51.32833\mathrm{}\pm 0.07$. The usual distortion-free rotational constants derived from these Watson constants are (in MHz): for DTO, $A^{\prime }=410\mathrm{}160.3$, $B^{\prime }=172\mathrm{}050.2$, $C^{\prime }=119\mathrm{} 183.6$; and for HTO, $A^{\prime }=677\mathrm{} 777.7$, $B^{\prime }=198\mathrm{} 089.7$, $C^{\prime }=150\mathrm{} 604.4$. The latter constants and corresponding ones previously obtained for other isotopic species of water were used to calculate substitutional structures of the molecule. The averages of the structural parameters thus obtained are 0.9577 Å for the bond length and 104.66° for the bond angle.

We have measured the relative optical excitation function and the polarization of the 6708-Å line, using crossed beams of electrons and lithium-6, for electron energies from threshold to 1400 eV. The electron energy resolution was ∼0.25 eV, and the lithium-beam optical depth was small and varied. We have normalized our excitation function to Born theory at 1404 eV, where the energy dependence has converged to the theoretical behavior. Between 2 and 6 eV, the measured cross section is (10-45)% smaller than the results of the most recent close-coupling calculations, but the measured polarization $P$ agrees with these theories within 20% of $P$. The theoretical polarization at threshold is not observed with our energy resolution.

The direct and exchange-core-polarization (ECP) contributions to the hyperfine interaction in the excited states, $3s$ to $10s$, of the sodium atom are obtained from first-principles one-electron calculations. The exchange-core-polarization results indicate that this effect is a nearly constant fraction of the direct effect for all the excited states considered. Using the difference between experiment in the two states where data are available and the total theoretical one-electron contribution as a measure of the correlation effect, we find a significant decrease in the percentage importance of the correlation effect in going from the ground $3s$ to the excited $4s$ state. Physical explanations are offered for this behavior and the near constancy of the fractional ECP contribution.

The problem considered is that of two identical two-level atoms a fixed distance $r$ apart, one of which is excited at $t=0\mathrm{}$. A simple improvement on the usual on-shell approximation (which in the single-atom case is part of the Weisskopf-Wigner approximation) yields new solutions for the various probability amplitudes in the form of infinite series involving all the retardation times $\frac{\mathrm{nr}}{c}$. The truncated solutions involving only the single retardation time $\frac{r}{c}$ are compared with previously published results both when all photon modes are allowed and when only photons propagating along the interatomic axis are allowed. When the retardation times are neglected, the series are summed to give the well-known results of Stephen and others.

Using the $\frac{1}{Z}(=\lambda )$ perturbation format, analytical properties of eigenstates in the complex $\lambda$ plane have been studied for two- and three-electron atoms, using simple nonlinear variational calculations. The ground states for both systems are included, as well as four excited states for two electrons. The results suggest a general partitioning of bound states into two categories: (i) If the singly charged anion is bound, analytical continuation in $\lambda$ along the positive real axis causes the energy to penetrate the continuum, and subsequently to terminate at a branch point. (ii) If the singly charged anion is unbound, the energy is tangent to the continuum edge, and analytic continuation in $\lambda$ to larger positive values creates a non-normalizable wave function.

Using two trial wave functions for a nonlinear variational study, the ground state of the two-electron isoelectronic sequence has been investigated for a continuously variable electron-electron coupling constant $\lambda$. These calculations extend the analogous study of the preceding paper by including explicit angular correlation on the one hand, and extra orbital flexibility on the other hand. The results confirm the earlier conclusion that for sufficiently large positive $\lambda$ (corresponding to nuclear charge $Z<\mathrm{}1\mathrm{}$) the ground-state energy penetrates into the continuum as a localized "bound" state, before terminating at a branch-point singularity.

The $E-H$-gradient balance technique has been used to measure the static electric dipole polarizabilities of the alkali-metal atoms and the tensor polarizabilities of the ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ metastable noble-gas atoms. All of the measurements are normalized to the scalar polarizability of ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ metastable helium, a value which has been accurately calculated. The scalar polarizabilities of the alkali atoms, in units of ${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^3$, are for lithium, 24.3 ± 0.5; sodium, 23.6 ± 0.5; potassium, 43.4 ± 0.9; rubidium, 47.3 ± 0.9; cesium, 59.6 ± 1.2. For the ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ metastable noble-gas atoms we measure the $\mathrm{zz}$ components of the polarizability tensors for $m_J=1\mathrm{} \mathrm{and} 2$, which completely determines the polarizability tensors for all $m_J$. For ${\alpha }_{\mathrm{zz}}\left(m_J\right)$ we find, in units of ${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^3$, for neon, 28.4 ± 0.6 ($m_J=1\mathrm{}$) and 26.7 ± 0.5 ($m_J=2\mathrm{}$); argon, 49.5 ± 1.0 ($m_J=1\mathrm{}$) and 44.7 ± 0.9 ($m_J=2\mathrm{}$); krypton, 52.7 ± 1.0 ($m_J=1\mathrm{}$) and 46.8 ± 0.9 ($m_J=2\mathrm{}$); xenon, 66.6 ± 1.3 ($m_J=1\mathrm{}$) and 57.4 ± 1.1 ($m_J=2\mathrm{}$). The rare-gas results, while more precise, are in good agreement with earlier work. The alkali-metal results are in excellent agreement with recent theory and the experiment of Hall and Zorn.

The electric dipole polarizability of the alkali-metal atoms Na, K, Rb, and Cs are determined by measuring the deflection of a velocity-selected beam by an inhomogeneous electric field. It is shown experimentally that scattering of slower beam atoms by background gas in the apparatus is an important systematic error in measurements of this kind if a beam-velocity selector is not used, and that this scattering is responsible for the discrepancies between different, earlier beam-deflection measurements of polarizability. The polarizability values obtained in this work are $\alpha \left(\mathrm{Na}\right)=24.4\mathrm{}\pm 1.7$ ${\mathrm{\AA }}^3$, $\alpha \left(\mathrm{K}\right)=45.2\mathrm{}\pm 3.2$ ${\mathrm{\AA }}^3$, $\alpha \left(\mathrm{Rb}\right)=48.7\mathrm{}\pm 3.4$ ${\mathrm{\AA }}^3$, and $\alpha \left(\mathrm{Cs}\right)=63.3\mathrm{}\pm 4.6$ ${\mathrm{\AA }}^3$.

$K$-shell ionization cross sections for protons over the energy range of 0.4 to 2.0 MeV have been measured on thin targets of the elements Se, Br, Rb, Sr, Y, Mo, and Pd. Total x-ray and ionization cross sections for the $K$-shell are reported. The experimental values of the ionization cross sections are compared to the nonrelativistic plane-wave Born approximation, the binary-encounter approximation, the constrained binary-encounter approximation, and the plane-wave Born approximation with corrections for Coulomb-deflection and binding-energy effects.

The recently derived generating function $I_p({\lambda }_1,{\lambda }_2;q)$ in the Glauber amplitude for $2{}_{}{}^1{}_{}{}^{}P$ excitation of He by electron impact is used to evaluate the cross sections for the $3{}_{}{}^1{}_{}{}^{}P$ and $4{}_{}{}^1{}_{}{}^{}P$ excitations of He by electron impact with incident energies from 50 to 1000 eV. Comparison is made with the Bethe approximation, the Born approximation, and the classical theory of Gryzinski. The theoretical results for the total excitation cross sections are in reasonable agreement with the experimental data. The positions of the peak values for the total cross section for both cases are found to be around 100 eV, which are consistent with the existing experimental findings. The $n^{-3\mathrm{}}$ rule is also briefly discussed. The polarization fraction of the 5016-Å helium line emitted in $e^{-}+\mathrm{He}$ collisions is also calculated in the Glauber approximation. The theoretical results for the polarization fraction are in reasonable agreement with the existing experimental data in the energy range $50<\mathrm{}{E}_a<1000\mathrm{}$ eV.

Total $L$-shell ionization cross sections were measured for Pr, Eu, Gd, and Dy over the energy range 0.3-0.2 MeV and compared to the nonrelativistic plane-wave Born approximation (PWBA), the constrained binary-encounter approximation (CBEA), and the binary-encounter approximation. Both the PWBA and CBEA predicted the measured values. Also the $\frac{L{\alpha }_{1,2}}{\mathrm{Ll}}$, $\frac{L{\alpha }_{1,2}}{L{\gamma }_1}$, $\frac{L{\alpha }_{1,2}}{L{\gamma }_{2,3}}$, and $\frac{L{\gamma }_1}{L{\gamma }_{2,3}}$ ratios were measured and compared with PWBA and CBEA. The results showed that the CBEA and PWBA accurately predicted the $L_{\mathrm{II}}$- and $L_{\mathrm{III}}$-subshell ionization cross sections, while only the PWBA accurately predicted the $L_{\mathrm{I}}$-subshell ionization cross section.

The cross sections for electron capture by positrons from atomic hydrogen are calculated using the second Born approximation and the method of Padé approximants for incident positron energy ranging from 12 to 500 eV. The results are compared with those obtained in the first Born approximation and other theoretical calculations. The contributions from the intermediate states higher than the first to the second-order rearrangement scattering amplitude are found to be significant. The nature of the variation of the second Born and the Padé differential cross sections with the angle of scattering is discussed.

The cross sections for Lyman-$\alpha$ production by the processes ${\mathrm{H}}^{+} (or {\mathrm{D}}^{+})+\mathrm{H}\mathrm{}\left(1S\right)\mathrm{}\to {\mathrm{H}}^{+} (or {\mathrm{D}}^{+})+\mathrm{H}\mathrm{}\left(2P\right)\mathrm{}$ (direct excitation) and ${\mathrm{H}}^{+} (or {\mathrm{D}}^{+})+\mathrm{H}\mathrm{}\left(1S\right)\mathrm{}\to \mathrm{H}\mathrm{}\left(2P\right)\mathrm{} \left[\mathrm{or}\mathrm{D}\mathrm{}\right(2P\left)\right]+{\mathrm{H}}^{+}$ (charge transfer) have been measured over the energy range 0.75-29 keV using a modulated cross-beam technique with liquid-helium cryopumping. Signals from the direct excitation and the charge transfer were separated by a Doppler-shift technique. The absolute cross sections were assigned by comparison with excitation of Lyman-$\alpha$ on electron impact. For direct excitation, general agreement in shape with the data of Stebbings et al. and of Morgan, Geddes, and Gilbody was found except for structure at 1.3 keV. The pseudostate calculations of Cheshire, Gallaher, and Taylor predicted the present experimental points well. For charge transfer, our results agree with those of Morgan, Geddes, and Gilbody at energies higher than 11 keV and have similarity in shape to the work of Stebbings et al. A peak appeared in our cross-section curve at the energies around 1.7 keV. Acceptable agreement with the pseudostate calculations was found up to the maximum energy except for the appearance of the peak at 1.7 keV.

A high-resolution double-focusing electrostatic electron analyzer has been used to resolve Ne Auger electrons produced by 0.15-6.0-MeV ${\mathrm{H}}^{+}$, 1.0-MeV ${\mathrm{He}}^{+}$, and 33-MeV $0^{5+}$ bombardment. Individual $K$-Auger satellite lines stemming from the decay of multiply ionized neon have been observed. The energies, relative intensities, and production probabilities of these satellite lines were measured as a function of the projectile $Z$ and as a function of proton bombarding energy. Tentative identifications for all observed lines were made by comparison with calculated Auger satellite transition energies. The reliability of the Hartree-Fock calculations used was demonstrated by comparison with $e^{-}+\mathrm{Ne}$ data and by comparing calculated x-ray transition energies for multiply ionized neon to recent measurements of O + Ne x-ray lines. A rough estimate of the probability of single- and double-$2s$ orbital vacancy production as a function of $L$-shell defect was obtained. With proton bombardment, the satellite-production probability $Q_s$ was observed to decrease smoothly with increasing proton energy. The observation that $Q_s$ for 6-MeV proton bombardment was approximately equal to that obtained with equal-velocity electrons is believed to imply that electron shakeoff is the dominant $L$-shell ionization mechanism for high-energy proton bombardment.