We report the first observation of the atomic cascade $9{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}-7{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ in mercury. The exponential distribution of time delays between detection of the $9{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}-7{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ (5676-Å) photon and the $7{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ (4358-Å) photon was measured, and a value of 8.2(0.2) nsec was obtained for the mean lifetime of the $7{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ level.

$K$ and $L$ x-ray transition probabilities have been calculated for several elements between $Z=92\mathrm{} \mathrm{and} 170$. The calculations include multipoles higher than $E1\mathrm{}$, are relativistic, and utilize Dirac-Hartree-Fock wave functions with finite-size nuclei. At these very high atomic numbers many transition rates go through a maximum as a function of $Z$, and other transitions show a maximum and a minimum, and then begin to increase again past $Z=150\mathrm{}$.

A new method, suggested by work of Otten, involving Zeeman scanning of an optically pumped vapor has been developed and used to determine the hyperfine structure of 3.5-h ${}_{}{}^{193}{}_{}{}^{}\mathrm{Hg}$ ($I=\frac{3}{2}$) in the $6s6p{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state, and the isotope shift in the 2537-Å resonance line. The $6s^2{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ ground state is optically pumped via each of the hfs components. The displacements of the ${}_{}{}^{193}{}_{}{}^{}\mathrm{Hg}$ hfs components from ${}_{}{}^{198}{}_{}{}^{}\mathrm{Hg}$ are found by measuring the magnetic field used to scan the optical-pumping lamp. The resonance is detected optically. The measured values are 83(4), 572(5), and 911(5) mK for the $F=\frac{5}{2},\frac{3}{2}, \mathrm{and} \frac{1}{2}$ components, respectively. The final results are 80(7) and 572(5) mK for the positions of the first two components corrected to account for perturbations caused by the presence of other isotopes. These perturbations are much smaller than the ones encountered in optical spectroscopy because of the selective nature of our detection method. A model calculation for the relevant emission and absorption processes was developed to determine the perturbations. We obtain, with the use of the previously determined $A$ value, the corrected quadrupole interaction constant $B=+15\mathrm{}\left(7\right)\mathrm{}$ mK. The corrected isotope shift of ${}_{}{}^{193}{}_{}{}^{}\mathrm{Hg}$ relative to ${}_{}{}^{198}{}_{}{}^{}\mathrm{Hg}$ is 383(7) mK. The resulting corrected odd-even staggering parameter, relative to ${}_{}{}^{192}{}_{}{}^{}\mathrm{Hg}$ and ${}_{}{}^{194}{}_{}{}^{}\mathrm{Hg}$, is $\gamma =0.74\mathrm{}\left(30\right)\mathrm{} or 0.56\left(14\right)\mathrm{}$, the two values corresponding to different measurements of the isotope shift of ${}_{}{}^{192}{}_{}{}^{}\mathrm{Hg}$.

Asymmetric line shapes in the $B\to A$ system of the deutroxyl radical have been observed. For the $P_{2}20$, $P_{1}20$, $P_{2}20$, and $P_{1}21$ transitions of the (0, 9) band, the resonance widths are, in ${\mathrm{cm}}^{-1\mathrm{}}$, 0.4 ± 0.2, 1.1 ± 0.2, 0.4 ± 0.2, and 0.2 ± 0.1, respectively, and the line profile indices are +2.5 ± 0.5, -2.0 ± 0.5, -3.0 ± 0.5, and +5.0 ± 1.0, respectively.

The theory of the spin-rotation interaction is discussed and its relation to the paramagnetic part of the magnetic shielding tensor derived with consistent treatment of the electric field in the molecule. The latter point yields agreement between theory and experiment for the first time in the case of isotopes of the hydrogen molecule. The paramagnetic part of the shielding constant for ${\mathrm{H}}_2$ ($J=1\mathrm{}$) is found to be -5.66(6) × ${10}^{-6\mathrm{}}$ in the gauge where the vector potential is zero at the nucleus.

The energy shifts of $K{\alpha }_2$, $K{\alpha }_1$, $K{\beta }_3$, $K{\beta }_1$, and $K{\beta }_2$ x rays were measured for the following Ru, Pr, and Yb compounds: Ru, Ru(C${\mathrm{O}}_2$)${\mathrm{Cl}}_2$, Ru${\mathrm{O}}_2$, [Ru${\left(\mathrm{N}{\mathrm{H}}_3\right)}_4$OHCl]Cl · 2${\mathrm{H}}_2$O, and Ru${\mathrm{F}}_3$; Pr, Pr${\mathrm{C}}_2$, ${\mathrm{Pr}}_2$${\mathrm{O}}_3$, PrFe${\mathrm{O}}_3$, ${\mathrm{Pr}}_6$${\mathrm{O}}_{11}$, Pr${\mathrm{O}}_2$, CsPr${\mathrm{F}}_5$, and ${\mathrm{Cs}}_2$Pr${\mathrm{F}}_6$, Yb, Yb${\mathrm{F}}_3$, and ${\mathrm{Yb}}_2$${\mathrm{O}}_3$. The results are compared with free-ion relativistic self-consistent-field calculations. The measurements bear out the dominant role of the $4f$ electrons in energy shifts between the trivalent and tetravalent Pr and the divalent and trivalent Yb. In Yb the full free-ion value is observed, while in Pr the free-ion value appears to be attenuated by a factor of 0.4, presumably owing to covalency. In all cases the relation of the x-ray energy shift to the Mössbauer isomer shift is discussed.

Hanle-effect measurements have been made on the $\left(5\mathrm{}{p}^{4}6s\right){}_{}{}^4{}_{}{}^{}P_{\frac{5}{2}}^{}{}_{}{}^{}$ state of iodine, which is connected to the ground state via the 1830-Å line. The atomic iodine is produced by thermal dissociation of ${\mathrm{I}}_2$, and is excited by unpolarized resonance radiation. Using the value of $g_J$ obtained by Keiss and Corliss from high-field Zeeman splittings, we find a radiative life-time of 57.9 ± 1.4 nsec (all errors quoted are 67% confidence limits). Neither coherence narrowing nor self-broadening is observed, and we place an upper limit of 200 ${\mathrm{\AA }}^2$ on the latter process. Cross sections for broadening of the Hanle effect by the rare gases are found to be (in ${\mathrm{\AA }}^2$): He: 9.8 ± 1.1; Ne: 19.5 ± 1.6; Ar: 37.6 ± 3.1; Kr: 38.7 ± 3.8; Xe: 49.2 ± 3.1. The relative values of these cross sections are seen to be in agreement with the predictions of a van der Waals interaction.

Two-Raman-photon emission in hydrogen atoms in the presence of an intense electromagnetic field has been calculated utilizing the method of Dalgarno and Lewis. We give a general formulation for ($n-2\mathrm{}$)-photon absorption and two-photon emission and also give numerical results for two-photon emission in the $1s-2p$ transition in hydrogen atoms. It is found that the emission of two spontaneous Raman photons could become important when the energy of the intense photon approaches the ionization energy. Finally, in the spectrum of the emitted Raman photon, faint lines are expected corresponding to the resonant peaks in the cross section.

The Faddeev equations for the ($e^{-},\mathrm{H}$) system have been solved numerically using separable expansions for both screened and unscreened versions of the Coulomb $t$ matrix. By considering the equations in uncoupled form, the convergence behavior of the binding energy and the singlet scattering length have been examined as the number of terms in the representation of the electron-electron potential has been increased. One to three states have been included in the $e-p$ interaction and up to twenty states in the $e-e$ interaction. Although the unscreened values are reasonable in low orders of truncation, the convergence is poor as more terms are included in the separable representations. To improve the rate of convergence, a screened form of the Coulomb $t$ matrix based on the Sturmian expansion of the Hulthén potential has been introduced. In the lowest trucation of the $e-p$ system, strong shielding of the $e-e$ interaction is necessary and convergence of both the binding energy and the scattering length can be achieved. In higher truncations of the $e-p$ system, where the representation of the $e-p$ interaction is more realistic, shielding is not effective in improving the rate of convergence within the practical limits of the calculations. The implications of the present calculations for the Faddeev approach to atomic three-body problems are discussed.

We report the observation of large projectile-structure effects in heavy-ion-induced $K$ x-ray yields from thin, light gas targets in a projectile energy region (∼ 1-4 MeV/amu) where molecular promotion effects are not expected to be significant. The $K$ x-ray yield from both projectile and target is found to be very sensitive to the ionic charge $q$ of the projectile. In some cases, notably for ${\mathrm{Ar}}^{q+}$ on Ne at 80 MeV and for ${\mathrm{Cl}}^{q+}$ on Ne at 42 MeV, the target yield increases exponentially with projectile charge, the projectile nuclear charge and velocity remaining constant. In all cases, the projectile $K$ x-ray yield increases faster than exponentially, even when the incident projectile has a full $K$ shell. It is evident that targets become highly ionized in these collisions, and already highly ionized projectiles are often further ionized in these targets of less-than-eqilibrium thickness. We discuss the limitations imposed on the determination of absolute x-ray cross sections in multiply ionizing collisions. These limitations cast serious doubt on the accuracy of $K$-shell ionization cross sections extracted from measured $K$ x-ray cross sections in this and other experiments. The projectile-target combination studied in the present experiment are ${\mathrm{Ar}}^{q+}$ on Ne (at 80 and 152 MeV), ${\mathrm{Cl}}^{q+}$ on Ne and S${\mathrm{F}}_6$ (at 42 and 50 MeV), and ${\mathrm{F}}^{q+}$ on two chlorine-bearing Freon compounds (at 43 MeV).

The interaction potential between a neutral molecule and a conducting surface is investigated through the study of the deflection of a beam of molecules by the conducting surface. The ultrahigh-vacuum system gave a vacuum below 5×${10}^{-11\mathrm{}}$ Torr, where the scattering by the residual gas is negligible in the deflection region of interest. An $r^{-3\mathrm{}}$ potential is predicted from a model in which the permanent dipole of the molecule interacts with its image in the surface of an ideal conductor. The measured deflection by the conducting surface does not agree precisely in form with this predicted potential. When this small difference in form is ignored, the observed interaction constants indicate that the model does, in fact, account for the major part of the interaction. These observed constants are from 0.42 to 0.68 of the predicted values. There remain unevaluated corrections arising from the finite resistivity of the conductor, and from a contribution by the fluctuation of the instantaneous dipole moment of the molecule from its statistical average (i.e., the permanent dipole moment).

$M$-series x-ray emission spectra from cerium have been recorded for near-threshold electron excitation. For incident electron energies near the $M_{\mathrm{V}}$ and $M_{\mathrm{IV}}$ inner-shell ionization energies, the spectra are dominated by intensity resonances of structures which are part of the continuous spectrum near its high-frequency limit. The intensity and position dependencies of the resonating structures are presented and are interpreted as arising from resonances in the cross sections for scattering electrons into empty $4f$ levels. No such resonances were observed for excitation energies near the $M_{\mathrm{III}}$ and $M_{\mathrm{II}}$ inner-shell ionization energies.

The Hanle effect has been used to measure the resonant pressure broadening of the $\mathrm{}\left(6p7s\right)\mathrm{}{}_{}{}^3{}_{}{}^{}P_1^0{}_{}{}^{}$ excited state of lead over a density range from ${10}^{14}$ to 4 × ${10}^{16}$ atom/${\mathrm{cm}}^3$. Below ${10}^{16}$ atom/${\mathrm{cm}}^3$ the results agree with theories based on the impact approximation and the experimental results of Happer and Saloman. For densities above ${10}^{16}$ atom/${\mathrm{cm}}^3$ it is shown that the broadening should have the form $\overline{v}{\sigma }_0^{\mathrm{}\left(L\right)\mathrm{}}[N-\beta N^2]$, where $\overline{v}$ is the mean relative velocity of the atoms, ${\sigma }_0^{\mathrm{}\left(L\right)\mathrm{}}$ is the resonant-collision-broadening cross section for the L th multipole element of the excited-state density matrix, $N$ is the atomic density, and $\beta$ is a measure of the correlation of the atoms which represents the breakdown of the impact approximation. $\beta$ has been determined to be equal to 3.8(6) × ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^3$.

Experimental ratios of $L$-subshell cross sections are given for ionization of lead and bismuth by 0.5-4-MeV-proton bombardment. The ratio of the $L_{\mathrm{II}}$ to $L_{\mathrm{I}}$ cross sections exhibits a maximum near 1.75 MeV. Individual subshell cross sections are obtained from the experimental ratios and previous total-cross-section data. These subshell ratios and cross sections are compared with the theoretical predictions of the plane-wave Born approximation using nonrelativistic hydrogenic wave functions, of the binary-encounter approximation scaled from Mg $K$-shell cross sections, and of the binary-encounter approximation scaled from cross sections obtained using $L$-shell velocity distributions. It was found that both approximations predict the trend of the data for the $L_{\mathrm{II}}$ and $L_{\mathrm{III}}$ subshells, but that only the plane-wave Born approximation gave the proper behavior for the $L_{\mathrm{I}}$ subshell.

The $L$-subshell ionization processes in Sm for proton bombardment over the energy range 0.3-2.0 MeV were studied using a thin Sm target (15.0 ${\mathrm{\mu }\mathrm{g}/\mathrm{c}\mathrm{m}}^2$). The total $L$-shell x-ray cross section and x-ray cross sections for the transitions $\mathrm{Ll}$, $L{\alpha }_{1,2}$, $L{\gamma }_1$, and $L{\gamma }_{2,3}$ were determined at each proton energy. Calculations for the total $L$-shell x-ray and ionization cross sections and $L$-subshell ionization cross sections were performed for the non-relativistic plane-wave born approximation (PWBA), constrained-binary-encounter approximation (CBEA), and binary-encounter approximation (BEA). Comparisons of the theoretical predictions are made to the experimental values for the total $L$ x-ray production cross section, total $L$-shell ionization cross section, relative intensities of 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, and the x-ray production cross sections for the $L{\alpha }_{1,2}$, $L{\gamma }_{2,3}$ and $L{\gamma }_1$ transitions. The results of this work show that the nonrelativistic PWBA theory is in reasonable agreement with the $L_I$-subshell processes measured in Sm for protons. The CBEA does not predict the appropriate structure observed in the $L_I$ subshell. The BEA calculations show that there are major differences between the data for Sm and the predictions of that theory.

Systematic measurements have been made on the $L{\beta }_{2,15}[L_3-N_{4,5}]$ and the $L{\gamma }_1[L_2-N_4]$ x-ray emission lines of the rare earths: ${}_{59}{}^{}{}_{}{}^{}\mathrm{P}\mathrm{r},$ ${}_{60}{}^{}{}_{}{}^{}\mathrm{N}\mathrm{d},$ ${}_{62}{}^{}{}_{}{}^{}\mathrm{S}\mathrm{m},$ ${}_{63}{}^{}{}_{}{}^{}\mathrm{E}\mathrm{u},$ ${}_{64}{}^{}{}_{}{}^{}\mathrm{G}\mathrm{d},$ ${}_{65}{}^{}{}_{}{}^{}\mathrm{T}\mathrm{b},$ ${}_{66}{}^{}{}_{}{}^{}\mathrm{D}\mathrm{y},$ ${}_{67}{}^{}{}_{}{}^{}\mathrm{H}\mathrm{o},$ ${}_{68}{}^{}{}_{}{}^{}\mathrm{E}\mathrm{r},$ ${}_{69}{}^{}{}_{}{}^{}\mathrm{T}\mathrm{m},$ and ${}_{70}{}^{}{}_{}{}^{}\mathrm{Yb}.\mathrm{}$ Each element was studied both in the metallic and oxidized states. The exchange interaction between the $4f$ and the $4d$ electrons splits both levels and results in sets of x-ray emission lines that are characteristic of the rare-earth elements alone, and that appear at the low-energy sides of the $L{\beta }_{2,15}$ and $L{\gamma }_1$ lines. A computer program was devised to unfold the complex structures, in order to obtain the energy separation and relative transition probabilities of the constituent lines. The effect of oxidation on the splitting of the $4d$ levels, although insignificant for low- and high-$Z$ elements, was found to be more than expected for elements with atomic number in the neighborhood of 65. It is quite possible that the structures studied consist of more than two discrete emission lines; that is, each of the $4d$ levels splits into more than two levels, expecially in the low-atomic-number elements. A theoretical interpretation of these results as a simple exchange interaction does not fit the results satisfactorily, so that more theoretical work is needed.

The relative cross sections for simultaneous ionization and excitation of helium by 200-eV electrons into the $4S$, $4P$, $4D$, and $4F$ levels have been measured via a fast delayed-coincidence technique. Results are in poor agreement with Born-approximation calculations for simultaneous ionization and excitation of helium, the $4P$ component being larger than expected.