Collisional excitation rates from the ground state to the $4f$ levels in lithiumlike Ne VIII have been derived from the absolute intensity of the $3{}_{}{}^2{}_{}{}^{}D-4\mathrm{}{}_{}{}^2{}_{}{}^{}F$ radiative transition. At temperatures of the order of the excitation energy and within the ∼ 30% relative accuracy, the magnitude of these $\Delta l=3\mathrm{}$ rates is equal to that for the corresponding $\Delta l=1\mathrm{}$ dipole rates to the $4p$ levels. For the purpose of these measurements the Ne VIII $3{}_{}{}^2{}_{}{}^{}D-4\mathrm{}{}_{}{}^2{}_{}{}^{}F$ doublet has been identified.

The loss processes of ions observed in photo-ionized ${\mathrm{Br}}_2$ have been studied by determining the time dependence of the ion number densities in the afterglow using quadrupole mass analysis techniques. The most abundant initially observed negative ion was ${\mathrm{Br}}^{-}$. This species was found to convert to $\mathrm{Br}_3^{}{}_{}{}^{-}$ in the afterglow by the three-body reaction ${\mathrm{Br}}^{-}$+2${\mathrm{Br}}_2$→ $\mathrm{Br}_3^{}{}_{}{}^{-}$ +${\mathrm{Br}}_2$. The coefficient for the process was found to be $k_c=2.9\mathrm{}\times {10}^{-29\mathrm{}}$ ${\mathrm{cm}}^6$/sec at 296 °K. The negative-ion—positive-ion ambipolar diffusion coefficients ($D_{a-}p$) for ${\mathrm{Br}}^{-}$ and $\mathrm{Br}_3^{}{}_{}{}^{-}$ were found to be 12.9 and 7.5 ${\mathrm{cm}}^2$ Torr/sec, respectively. The $\mathrm{Br}_3^{}{}_{}{}^{-}$ species was found to decay mainly by ion ambipolar diffusion. The positive-ion species ${\mathrm{Br}}^{+}$, $\mathrm{Br}_2^{}{}_{}{}^{+}$, and $\mathrm{Br}_3^{}{}_{}{}^{+}$ were observed in the afterglow. Of these, the $\mathrm{Br}_2^{}{}_{}{}^{+}$ ion was initially most abundant. Although a rapid reaction involving ${\mathrm{Br}}^{+}$ takes place in the early afterglow, $\mathrm{Br}_2^{}{}_{}{}^{+}$ and $\mathrm{Br}_3^{}{}_{}{}^{+}$ decay mainly by diffusion. $D_{a+}p$ for the $\mathrm{Br}_2^{}{}_{}{}^{+}$ was determined to be 12.6 ${\mathrm{cm}}^2$ Torr/sec for the case where the electron number density has decayed to zero and the predominant negative ion was ${\mathrm{Br}}^{-}$. The ambipolar diffusion coefficient for $\mathrm{Br}_3^{}{}_{}{}^{+}$ was found to be essentially identical to that for the $\mathrm{Br}_3^{}{}_{}{}^{-}$ ion under the conditions where the $\mathrm{Br}_3^{}{}_{}{}^{+}$ ion and $\mathrm{Br}_3^{}{}_{}{}^{-}$ ion were the predominant ion species present.

Electrons emitted from foil-excited beams of ${\mathrm{F}}^{6+}$ and ${\mathrm{O}}^{5+}$ ions (2.5-20 MeV) have been energy analyzed and their number measured versus distance from the foil. Lines associated with the $\mathrm{}\left(1s2s2p\right)\mathrm{}{}_{}{}^4{}_{}{}^{}P_{\frac{5}{2}}^{}{}_{}{}^{}$ level and with higher quartet levels are observed to decay at various rates. Life-times for the $\mathrm{}\left(1s2s2p\right)\mathrm{}{}_{}{}^4{}_{}{}^{}P_{\frac{5}{2}}^{}{}_{}{}^{}$ state in ${\mathrm{F}}^{6+}$ and ${\mathrm{O}}^{5+}$ are found to be (1.5 ± 0.1) and (2.5 ± 0.3) × ${10}^{-8\mathrm{}}$ sec, respectively. The latter disagrees with earlier experimental work and with theoretical estimates.

Auto-ionizing states in Cs between 12 and 20 eV have been studied by electron impact. The retarding-potential-difference method was used to obtain an electron beam with energy spread of about 0.1 eV. To determine the threshold energies, inelastically scattered electrons were analyzed by the trapped-electron method. We have been able to identify about 20 levels, and the agreement with spectroscopic data is excellent. A peak appearing at 12.80 eV is probably due to the quartet states observed by Feldman and Novick.

The $K\alpha$ and $K\beta$ x rays of Ni produced by the passage of light fission fragments from the spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ through a thin Ni foil were found to be shifted up in energy by 69 ± 11 and 210 ± 16 eV, respectively, relative to the x rays produced by 6-MeV $\alpha$ particles and by photons from the decay of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$. These shifts are similar in character to those observed previously in 15- MeV oxygen-ion bombardments, but require extremely high ionic charge states to be explainable in terms of multiple inner-shell plus outer-shell ionization.

Precise ${\mathrm{F}}^{19}$ NMR chemical shift measurements have been made on gaseous C${\mathrm{F}}_4$ and Si${\mathrm{F}}_4$ at different temperatures and pressures and a distinct nonlinear temperature dependence has been found. It is shown that this effect can be adequately explained with the help of a London dispersion field and a field due to repulsion. Present work is compared with ${\mathrm{Xe}}^{129}$ results.

The energy separation $\mathcal{S}$ between the $2{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ and $2{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ states of singly ionized helium was measured using a microwave method. Helium atoms in the space between the plates of a spherical-mirror Fabry-Perot resonator are bombarded continuously by electrons of 200-eV energy to produce helium ions in the $2{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ metastable state. The applied modulated rf power induces transitions in the metastable ions to the short-lived $2{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ state. The 40.8-eV photons emitted by the decay of the $2{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ ions to the ionic ground state $1{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ are quantum converted to visible photons by a scintillator and are then guided to a photomultiplier. The output of the photomultiplier is detected and amplified synchronously with the rf power. The experiment made use of the Zeeman effect of the fine structure and is performed in an applied homogeneous magnetic field. Three different operating values for the helium pressure are used and the result is extrapolated to a zero-pressure value. A through search was made for all possible systematic errors in the experiment. The value for $\mathcal{S}$ thus obtained is 14 046.2 ± 2.0 MHz. The quoted uncertainty consists of three standard deviations for the statistical error plus estimates of systematic errors. This result agrees with the previous experimental values for $\mathcal{S}$ (within three standard deviations), and with the latest theoretical value of 14 044.5 ± 5.2 MHz.

An experimental study has been made of the excitation of the ArII spectrum in low-energy (10-1000 eV) ${\mathrm{He}}^{+}$ + Ar collisions. The principal states excited, which have lines from 3500 to 5200 Å, have been positively identified. The dependence of excitation on energy has been measured for six states. It is found that states with ${}_{}{}^1{}_{}{}^{}D$ parent terms are generally stronger and have more rapid rise with energy at threshold than states with ${}_{}{}^3{}_{}{}^{}P$ parent terms. The effect of cascade from higher excited states on the intensities of the strongest lines has been studied. The energy dependence of one state is compared with the form expected from a simple Landau-Zener model.

Spectra of inelastically scattered electrons from Al and Au targets are shown for scattering angles of 45 and 135 deg at incident electron energies of 0.2, 1.0, and 2.0 MeV, and for an angle of 60 deg at an energy of 1.0 MeV. Theoretical values from the Bethe-Heitler theory, calculated from the formulas of McCormick, Keiffer, and Parzen, are compared to the measured values.

The proton-on-helium elastic-scattering differential cross section is computed through the rainbow region for two different potential surfaces, each of high accuracy, for center-of-mass energies 92.7 and 15.4 eV (115.8 and 19.3 eV in the lab frame) to test an assumption that the semiclassical approximation would give adequate information at the rainbow angle to distinguish experimentally the better of the theoretical potentials.

Kinetic energies of metastable O atoms formed in dissociative excitation of ${\mathrm{O}}_2$ were measured by a time-of-flight experiment. Metastable $\mathrm{O}\left({}_{}{}^5{}_{}{}^{}S_{}^0{}_{}{}^{}\right)$ atoms (9.14 eV) as well as high-lying states near the ionization limit of O (13.6 eV) were detected by means of Auger ejection of secondary electrons from a Cu-Be surface. The energy spectra of metastable fragments showed distinct structure with maxima near 0.3 and 2eV. Repulsive-potential-energy curves of ${\mathrm{O}}_2$ were constructed from the measured energy spectra and time-resolved excitation functions. The excitation function for the direct excitation of the $\mathrm{O}\left({}_{}{}^5{}_{}{}^{}S_{}^0{}_{}{}^{}\right)$ state had a threshold of 14.3 ± 0.2 eV which is equal to the minimum energy for dissociatively exciting the $\mathrm{O}\left({}_{}{}^5{}_{}{}^{}S_{}^0{}_{}{}^{}\right)$ state. Using selection rules and symmetry arguments concerning the angular variation of dissociation products, the molecular state reached near 14.3 eV was identified as a ${\Pi }_u$ state with a probable multiplicity of 3. Other molecular states reached at higher energies were not identified. It seems, however, that there was a sizable contribution due to O atoms in high-lying Rydberg states excited in dissociative excitation. The differential cross section for the direct formation of $\mathrm{O}\left({}_{}{}^5{}_{}{}^{}S_{}^0{}_{}{}^{}\right)$ was found to be $\frac{d\sigma }{d\Omega }\simeq 1\times {10}^{-19\mathrm{}}$ ${\mathrm{cm}}^2$/sr within a factor of 2 at an electron energy of 30 eV and an angle of 90° with respect to the electron beam. Several atmospheric applications of the measurements concerning the heating of the atmosphere, radiative transfer of resonance radiation, and chemical reactions are mentioned briefly.

A crossed-beam technique was used to measure total nonresonant charge-transfer cross sections of the following reactions over an energy range from about 0.5 to 20 keV: ${\mathrm{Li}}^{+}$ + Cs→ Li + ${\mathrm{Cs}}^{+}$, ${\mathrm{Li}}^{+}$ + Rb→ Li + ${\mathrm{Rb}}^{+}$, ${\mathrm{Li}}^{+}$ + K → Li + ${\mathrm{K}}^{+}$, ${\mathrm{Hg}}^{+}$ + Cs→ Hg + ${\mathrm{Cs}}^{+}$. For each reaction, the minimum energy defect occurs for transfer to an excited state. The cross sections show typical nonresonant characteristics with the measured maxima corresponding to these energy defects. The production of photons resulting from deexcitation of the Li ($2p$) state formed by charge-transfer collisions was also measured over the same energy range for the reactions involving Li. These photon cross sections (with larger experimental uncertainties than the total cross sections) were "normalized" to the total cross section in the near-adiabatic region using semiempirical relationships. Transfer to an excited state is the dominant channel in the near-adiabatic region with transfer to the ground state becoming increasingly important with increasing impact velocity. The discussion of the ${\mathrm{Hg}}^{+}$ + Cs results includes statistical weight considerations.

Cross sections are computed for the elastic and fine-structure excitation scattering of singly ionized carbon atoms by low-energy (less than 0.1 eV) hydrogen atoms. A close-coupling formulation is employed and the scattering equations are solved in a coupled-angular-momentum representation. The correct energy defect between the ${\mathrm{C}}^{+}\left({}_{}{}^2{}_{}{}^{}P\right)$ fine-structure levels is included. For the first time, both spin-change and long-range electrostatic coupling terms are explicitly included in the scattering equations. The calculated ${\mathrm{C}}^{+}$-H excitation cross section varies from 4.87×${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ at 0.01 eV to 2.86×${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ at 0.085 eV, and the maximum of almost 5.60×${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ occurs near 0.015 eV. The spin-change coupling, described herein, is found to be much more important than the long-range electrostatic coupling at all energies considered.

We utilize the analytic atomic independent-particle model (IPM) of Green, Sellin, and Zachor as a basis for calculating generalized oscillator strengths for the single-particle excitations of Ne, Ar, Kr, and Xe. First, we establish averages of the experimental energy levels to arrive at single-particle states. We then adjust the two parameters so that the IPM potentials accurately characterize these excited-state energies. Using the wave functions associated with these potentials and the Born approximation, we calculate the generalized oscillator strengths for excitations to $p^5\mathrm{ns}$ states. A very complex nodal structure is apparent at large values of momentum transfer and a rapid decline in magnitude occurs after the second node. We may accurately characterize the results up to the second node with a convenient analytic form which leads to analytic total excitation cross sections. We use available optical oscillator strengths to normalize our results. The systematics and regularities of the parameters for various Rydberg series are discussed and approximate scaling laws are given.

A distorted-wave (DW) formulation with exchange is given for the electron impact excitation of the rare gases from ${\left(n_{0}p\right)}^6$ to ${\left(n_{0}p\right)}^5\mathrm{nl}$ configurations. A practical form employing the pure $\mathrm{LS}$-coupling scheme is used in conjunction with the phenomenologically determined independent-particle model (IPM) and the DW potentials of real central forms to compute cross sections averaged over fine structures. Numerical work is carried out for $\mathrm{Ne} 2p\to 3s$ and $\mathrm{Ar} 3p\to 4s$ electron impact excitations. The distorted generalized oscillator strengths (DGOS), which converge to the generalized oscillator strengths (GOS) in the limit of the Born approximation, as well as integrated cross sections, are obtained over a wide range of energies, so that the systematic variation of the cross sections in relation to the results of the Born approximation can be studied. The results of the angular distributions at lower energies are in reasonable agreement with the data by Nicoll and Mohr.

The collisional transfer of energy between two excited states in a gas discharge may be described by a two-body inelastic cross section. The energy dependence of the two-body cross section for collisions of the second kind between the $\mathrm{He} 2{}_{}{}^1{}_{}{}^{}S$ metastable and $\mathrm{Ne} 3s_2$ states has been investigated. This process is primarily responsible for populating the upper level of the 6328-Å laser transition. Pulsed afterglow measurements were performed as a function of gas temperature and pressure. The experiments were conducted at low gas temperatures so that the effect of energy transfer from the helium metastable level to other nearby neon levels could be minimized. The measured decay rates departed substantially from that predicted by using an energy-independent cross section. A unit-step cross section for the $\mathrm{He} 2{}_{}{}^1{}_{}{}^{}S-\mathrm{Ne} 3s_2$ resonant transfer process with a value of (1. 0 ± 0. 15) × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ and with a threshold energy corresponding to the energy difference between the two levels was determined.

The Schrödinger equation for two electrons in a Coulomb field is studied in the critical region where both electrons have near-zero kinetic energies. The main feature of this problem is that the mutual screening between the two electrons determines and is determined by the partition of the available energy between them. This energy-dependent screening can be taken into account to yield a complex potential in the radial variable $R={(r_1^2+r_2^2)}^{\frac{1}{2}}$ of the six-dimensional configuration space of the two electrons. Solutions of this equation are obtained and are shown to correspond to the classical orbits given in an early paper by Wannier. A possible way is indicated of using these wave functions to establish the Wannier threshold law which, for ionization of neutral atoms, is $\sigma \propto E^{1.127}$. Finally, the interplay between the total energy and the Coulomb potential is discussed both for this problem and for the case of one electron in the field of a nucleus.

By restricting attention to a single open scattering channel at a time, it is found that an optical potential, accurate to second order in the scattering potential, can be easily derived for the example of rotational excitation of a rigid rotator by a structureless atom. The resulting equations are contrasted with those derived from the close-coupling method. In cases where many open channels are present, the optical-potential method seems to offer many advantages over close coupling. Various practical methods for improving the accuracy of the optical potential beyond second order are discussed.

Equilibrium charge-state distributions have been determined experimentally for chlorine and bromine ions with energies between 1 and 14 MeV traversing ${\mathrm{H}}_2$, He, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, Ar, and Kr gases and a carbon foil. In addition, a few measurements have been made using iodine beams traversing various targets—at 3, 10, and 12 MeV through carbon foil, at 8 MeV through C${\mathrm{O}}_2$, at 10 and 12 MeV through gold foil, and at 12 MeV through a Xe gas target.

Molecular-dynamic studies of the kinetic correlation functions for shear viscosity and heat conductivity of hard disks are consistent with the asymptotic reciprocal time behavior $\frac{1}{S}$ predicted by hydrodynamics. However, this hydrodynamic description, which predicts divergent transport coefficients, must be made self-consistent by introducing time-dependent transport coefficients, leading to a decay of $\frac{1}{S\sqrt{\left(\ln S\right)}}$, indistinguishable from the $\frac{1}{S}$ behavior. The hydrodynamic model predicts no such long-time behavior for the potential contributions.