The ${}_{}{}^1{}_{}{}^{}D\leftrightarrow {}_{}{}^3{}_{}{}^{}P$ and ${}_{}{}^1{}_{}{}^{}S\leftrightarrow {}_{}{}^1{}_{}{}^{}D$ transitions in ${\mathrm{N}}^{+}$ have been observed in the energy-change spectra of 1-4-keV ${\mathrm{N}}^{+}$ scattered from Kr and Xe. In contrast to the case for scattering from the lighter rare gases, the spin-nonconservative ${}_{}{}^1{}_{}{}^{}D\leftrightarrow {}_{}{}^3{}_{}{}^{}P$ transitions occur with high probability in the ${\mathrm{N}}^{+}$-Kr and ${\mathrm{N}}^{+}$-Xe collision systems.

Recent experimental data by Wang et al. on the temperature dependence of the momentum-accommodation coefficient between helium vapor and the liquid film are reanalyzed. New values are obtained which are several orders of magnitude below those given, and yield better agreement with measurements by Blair and Matheson.

The positions of the resonances calculated by the stabilization method can be improved by inclusion of the shift as given by Hazi and Fels. It is also indicated that the phase shifts calculated by the Harris method at incident energies corresponding to the stabilized roots give the positions and the widths of the resonances reasonably well.

Electron detachment cross sections for ${\mathrm{H}}^{-}$ and ${\mathrm{D}}^{-}$ on He, Ar, ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, and ${\mathrm{O}}_2$ were found to be essentially identical to within experimental accuracy when compared at equivalent velocities in the ${\mathrm{H}}^{-}$ collision energy range from 200 eV to 10 keV.

Differential cross sections for scattering of 300-500-keV ${\mathrm{H}}^{+}$, ${\mathrm{He}}^{+}$, and ${\mathrm{Li}}^{+}$ through 3-15° have been measured. The targets were 300-9000-Å-thick vacuum-deposited, self-supporting selenium foils. An empirical extrapolation procedure was used to correct for the influence of multiple scattering. The cross sections obtained agree well with the Thomas-Fermi theory, both with regard to scaling and to absolute magnitude.

Previously derived comprehensive formulas for the $\mathrm{Z}_1^{}{}_{}{}^3$ contributions to the ranges of charged particles in matter are amended to apply at high, nonrelativistic particle velocities.

We consider double light scattering by a simple fluid near its critical point. It is shown that Ornstein-Zernike-Debye plots of inverse total (single plus double) scattering intensity are not linear, but show downward curvature at small scattering angles near the critical point. This effect has been observed experimentally and is usually attributed to a nonzero value for the critical exponent $\eta$. We compare our conclusions with those of Splittorff and Miller, who have found that such downward curvature can also be caused by density gradients near the critical point.

The usefulness of the definition of diabatic states by Smith is questioned. His definition leads to an electronic basis which—except for phase factors—is independent of the internuclear separation.

The single-ion contributions, ${\rho }_i$, to alkali ($M$) halide ($X$) repulsive interactions of the form $A_{\mathrm{MX}}\mathrm{}\left(R\right)\mathrm{}{e}^{\frac{-R}{{\rho }_{\mathrm{MX}}}}$, with ${\rho }_{\mathrm{MX}}={\rho }_M+{\rho }_X$, are considered for two diatomic models. The ${\rho }_i$ values are shown to correlate linearly with the position of the outermost peak of the electron density distribution of the ion. A similar trend is observed in the single-ion contributions to the range parameter for the square of the $M-X$ overlap. Diatomic single-ion parameters are shown to differ for the two models although the combination rules are equally well obeyed. Single-ion contributions to the pre-exponential factors, "soft-sphere" radii, and repulsive interaction potentials for $M-M$ and $X-X$ are briefly discussed.

Relative measurements of the differential cross section for elastic scattering of ${\mathrm{Xe}}^{+}$ on Xe and ${\mathrm{Ar}}^{+}$ on Ar are reported in the energy range 20-340 eV and the angular range 1-15 deg (lab). The data are presented in terms of the reduced cross section $\rho \left(\theta \right)\equiv \theta sin\theta \sigma \left(\theta \right)$ and the reduced angle $\tau \equiv E\theta$. The $\rho -\mathrm{v}\mathrm{s}-\tau$ plots for ${\mathrm{Xe}}^{+}$ on Xe show complex oscillations which we attribute primarily to phase interference in scattering from three coherent pairs of gerade-ungerade potential curves. The six states involved are the electronic fine-structure states of $\mathrm{Xe}_2^{}{}_{}{}^{+}$, four of which dissociate to $\mathrm{Xe}+{\mathrm{Xe}}^{+}\left({}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}\right)$, and the other two to $\mathrm{Xe}+{\mathrm{Xe}}^{+}\left({}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right)$. At larger values of $\tau$ the elastic scattering pattern is further complicated by potential-curve crossings and excitation to higher states, while at smaller $\tau$ potential wells give rise to two rainbow peaks. We have resolved two oscillatory patterns in the data, from which we have determined two difference potentials for $\mathrm{Xe}_2^{}{}_{}{}^{+}$, $\Delta V_{\mathrm{JM}}\mathrm{}\left(R\right)\mathrm{}\equiv \left|V_{\mathrm{JMg}}\mathrm{}\right(R)-V_{\mathrm{JMu}}\mathrm{}(R\left)\right|:\Delta V_{\frac{3}{2},\frac{3}{2}}=23\mathrm{}{e}^{-1.23R}$, $3.5\lesssim R\lesssim 5.5$; and $\Delta V_{\frac{1}{2},\frac{1}{2}}=2.0\mathrm{}{e}^{-0.788R}$, $5\lesssim R\lesssim 6.5$, in a.u. The ${\mathrm{Ar}}^{+}$ on Ar data are in excellent agreement with scattering calculations based upon ab initio computations of the ${\Pi }_u$ and ${\Pi }_g$ potentials of $\mathrm{Ar}_2^{}{}_{}{}^{+}$.

By means of an optical detection technique, the electron-loss cross sections for He atoms in the excited states $3{}_{}{}^3{}_{}{}^{}P$, $4{}_{}{}^3{}_{}{}^{}S$, $4{}_{}{}^1{}_{}{}^{}S$, $5{}_{}{}^3{}_{}{}^{}S$, and $5{}_{}{}^1{}_{}{}^{}S$ have been measured in ${\mathrm{H}}_2$ in the energy range 8-160 keV. These cross sections are compared to theoretical cross sections derived by means of the classical impulse approximation of Bates and Walker. In agreement with this theory, the present electron-loss cross sections are found to depend very little on the binding energy and the specific quantum state of the weakly bound electron being removed. Further, they are approximately equal to the total electron-scattering cross section taken at the same impact velocity, as also predicted by the mentioned theory.

Relative emission cross sections have been measured for spectral lines in the vacuum ultraviolet region which are produced by collisions of ${\mathrm{He}}^{+}$ with Ar over a range of energies from threshold to 10 keV. The lines investigated arise from the following excited states of Ar and ${\mathrm{Ar}}^{+}$: for Ar, $3p^{5}4s[{}_{}{}^1{}_{}{}^{}P,{}_{}{}^3{}_{}{}^{}P]$; for ${\mathrm{Ar}}^{+}$, $3s3p^6{}_{}{}^2{}_{}{}^{}S$, $3d{}_{}{}^2{}_{}{}^{}P$, $3d{}_{}{}^2{}_{}{}^{}D$, $4s{}_{}{}^2{}_{}{}^{}P$, and $4s^{\prime }{}_{}{}^2{}_{}{}^{}D$. Charge exchange at low collision energies is dominated by transfer into the $3s3p^6$ states. The cross section for exciting this configuration rises rapidly from threshold at 4.7 eV to a low-energy maximum which occurs at 11.3 eV. By normalizing our data to the absolute emission cross section which has been determined by De Heer et al. at a collision energy of 2 keV, it is found that the cross section for exciting the $3s3p^6$ configuration is 5.4 × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ at the low-energy maximum. Oscillations are observed in several of the emission cross sections which indicate interferences between the wave functions of one or more of the excited states of the quasimolecule.

Collisional relaxation of spin polarization within the Cs atom has been studied using new techniques of white-light optical pumping. Analyses of pumping transient signals have been made including full treatments of effects due to the hyperfine interaction and spin exchange. The nuclear-spin-independent cross sections for relaxation of $〈S_z〉$ in the $6{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ state of Cs, at 288 °K, are (in ${10}^{-23\mathrm{}}$ ${\mathrm{cm}}^2$): Cs-He, 2.43 ± 0.24; Cs-Ne, 4.08 ± 0.40; Cs-Ar, 108 ± 10; Cs-${\mathrm{N}}_2$, 55.2 ± 5.5. The nuclear-spin-independent cross sections for relaxation of $〈J_z〉$ within the $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ state of Cs, at 288 °K, are (in units of ${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$): Cs-He, 12.5 ± 4.0; Cs-Ne, 6.9 ± 2.0. The Cs-buffer-gas diffusion coefficients, extrapolated to 273 °K, are (in units of ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$): Cs-He, 0.291 ± 0.030; Cs-Ne, 0.171 ± 0.017; Cs-Ar, 0.111 ± 0.011; Cs-${\mathrm{N}}_2$, 0.098 ± 0.010. There is no experimental evidence for contributions to low-pressure relaxation rates from the formation of Cs-buffer-gas van der Waals molecules, even in the case of Cs-Ar. There is, however, possible evidence for small contributions to relaxation rates at high buffer-gas pressures from this source.

For multiplets formed by adding an $s$ vacancy to an atom with a partially filled shell, it is shown that the Auger transition rate can be found from expressions that do not involve franctional-parentage coefficients of the partially filled shell. The proof requires a sum over final states and that the partially filled shell be in a state of maximum spin. Calculations are performed for the widths of the $4s$ and $5s$ multiplet components in the rare earths. The calculated $4s$ widths are considerably larger than the measured values, while the $5s$ widths are considerably smaller than the measured values. It is shown that these disagreements cannot be fully accounted for by the choice of Auger-electron energy. It is hypothesized that the cause of the disagreement is neglect of configuration interaction, and this is briefly discussed.

Crossed beams of ${\mathrm{Ba}}^{+}$ and electrons were used to measure the absolute emission cross sections for the ${\mathrm{Ba}}^{+}$ lines, 455.4, 493.4, 490.0, and 413.1+416.6 nm. Polarization fractions of the light were also measured. The data were analyzed to extract level excitation cross sections. The excitation cross section for the $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ level has a value 34.7×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ at the 2.72-eV threshold, shows marked structure in the 3-10-eV interval, and decreases to 1.71×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ at 747 eV. The polarization fraction for the 455.4-nm light exhibits pronounced oscillatory structure in the interval 3-7 eV. Excitation cross section for the $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$, $7{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, and $6{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}+\frac{5}{2}}^{}{}_{}{}^{}$ levels have values at threshold of 20.0×${10}^{-16\mathrm{}}$, 5.4×${10}^{-16\mathrm{}}$, and 4.3×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$, respectively. Total uncertainties at a "high-confidence level" are about ±10% for the $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ and $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ cross sections. Uncertainties range around ±30% for the $7{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ cross section and ±20% for the $6{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}+\frac{5}{2}}^{}{}_{}{}^{}$. Measurements for the $6{}_{}{}^2{}_{}{}^{}P$ cross sections agree at high energies with the Coulomb distorted-wave calculation of Sheorey and Burgess. Measurements for the $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ level are in quite good agreement with the measurements of Bacon and Hooper and of Pace and Hooper for energies 6 to 100 eV. However, the Pace and Hooper points at 3 and 4 eV are nearly twice the present values. Signals due to excitation of metastable $5{}_{}{}^2{}_{}{}^{}D$ ions in the ion beam were observed, and estimates could be made of the cross section for excitation from this state to the final states above. Cross sections at threshold were estimated to be 13.4×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$±34%, 9.8×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$±28%, 7.4×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$±100%, 6.9×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$±27% for excitation from the $5{}_{}{}^2{}_{}{}^{}D$ levels to the $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$, $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$, $7{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$, and $6{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}+\frac{3}{2}}^{}{}_{}{}^{}$ levels, respectively. The rate coefficients for excitation of $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ calculated from the data are in reasonable agreement with the measurements of Hinnov et al.

Using Fredholm techniques employing only square-integrable basis functions, elastic $s$- and $p$-wave singlet electron—hydrogen—atom cross sections are calculated for the energy range 10-27 eV, that is, at energies where a continuum of open channels is present. The $s$ and $p$ amplitudes are combined with higher partial-wave amplitudes taken from earlier close-coupling results,to give singlet $e-\mathrm{H}$ elastic angular distributions at and above the ionization threshold.

We present a high-energy calculation of the $K$ -shell ejection cross section $\sigma \left(Z_p\right)$ as a function of projectile charge $Z_p$. Charge-transfer effects are not included. The wave function for the heavy projectile is written as $e^{i{\overrightarrow{\mathrm{k}}}_0•\overrightarrow{\mathrm{R}}}\mathrm{F}(-in,1,i{k}_e|\overrightarrow{\mathrm{R}}-\overrightarrow{\mathrm{r}}|-i{\overrightarrow{\mathrm{k}}}_{\mathrm{e}}•(\overrightarrow{\mathrm{R}}-\overrightarrow{\mathrm{r}}\left)\right)\Gamma \mathrm{}(1+in)\mathrm{}{e}^{\frac{-n\pi }{2}}$, as opposed to the Glauber approximation $e^{i{\overrightarrow{\mathrm{k}}}_0•\overrightarrow{\mathrm{R}}}\exp (-in\int {-\infty }^Z\mathrm{dZ}{|\overrightarrow{\mathrm{R}}-\overrightarrow{\mathrm{r}}|}^{-1\mathrm{}})$. These two approximations agree at large distances but differ as the electron and projectile approach closely to each other. A prediction is made that if $T_m$ (the maximum classical energy an electron at rest may receive) is much greater than $I_K$ then $r_{12}$ will be less than unity. Here $r_{12}=\frac{\sigma \left(Z_1\right)Z_2^2}{\sigma \left(Z_2\right)Z_1^2}$, $Z_1>Z_2$. Higher-energy experiments are needed to confirm this theoretical result.

Differential cross sections for the elastic scattering of electrons from atomic and molecular hydrogen have been measured at 30, 50, 100, and 200 eV. The results for atomic hydrogen are compared with various theoretical calculations based on both low-energy and improved high-energy approximations. The ratios of the total cross sections for elastic scattering of electrons from atomic and molecular hydrogen are also given for incident energies of 9.4, 12.0, 20, 30, 50, 100, and 200 eV.

Calculations of ionization cross sections have been performed for removing electrons from $2s$ and $2p$ levels in hydrogenlike atoms by heavy-charged-particle impact using the binary-encounter approximation (BEA). The ratio of $\frac{{\sigma }_{L_{\mathrm{II}}}}{{\sigma }_{L_{\mathrm{I}}}}$ is predicted to peak when the projectile has a velocity equal to 0.3 times the velocity of the atomic electron. Experimental values of $\frac{{\sigma }_{L_{\mathrm{II}}}}{{\sigma }_{L_{\mathrm{I}}}}$, in agreement with Born predictions, peak at a velocity significantly lower than that predicted by BEA calculations. By transforming to coordinate space in an approximate way, predictions for the impact-parameter dependence are made. In the $2s$ case, the ionization probability has a pronounced local minimum for impact parameters near half the atomic radius, corresponding to a node in the $2s$ wave function. The ionization probabilities for arbitrary charged particles on arbitrary targets may be easily found by applying scaling laws to values tabulated over a wide range of projectile velocities.

A method is described for the measurement of relative subshell photoionization cross sections (SPCS) in the noble gases by the technique of ultraviolet photoelectron spectroscopy. Values are reported for the photoionization cross sections of the neon $2p$, krypton $4p$, xenon $5p$, and xenon $5s$ levels relative to that of the argon $3p$ level. The photon energies used for these measurements were 21.22, 40.81, and 48.37 eV. Approximate absolute subshell photoionization cross sections deduced from these relative cross sections are compared to other absolute SPCS obtained from total photoabsorption measurements and also from theory. Results of some relative photoionization cross-section measurements for the outer $p$ bands associated with the halide ions in solid alkali halides and the outer $d$ bands of metallic gold and silver are also presented. Close similarities in variation with photon energy and atomic number are found between the relative photoionization cross sections of the outer $p$ bands of the alkali halides and the outer $p$ levels of the noble gases, but the photoionization cross sections of the $d$ bands of both gold and silver exhibit quite different properties from those found for the outer $p$ bands and levels of both alkali halides and noble gases. A general conclusion is drawn concerning cross sections for photoionization from electron energy bands in solids.