The perturbation seen in the experimental differential elastic-scattering cross section for the 40-eV ${\mathrm{He}}^{+}$ + Ne system has been attributed to a single crossing of two intermolecular potential-energy curves. A new theoretical treatment of the curve-crossing problem, namely, that of Delos and Thorson, is employed to obtain the crossing probabilities and phases associated with the crossing. These are determined by utilizing ab initio potentials involved in the crossing and are further used in a partial-wave calculation of the cross section, which is compared with our experiment. The origin of the oscillatory structure observed in the differential cross section is discussed in semiclassical terms by defining the problem in terms of two pseudo-deflection-functions. A rainbow effect is shown to be related to a particular feature (a maximum rather than a minimum) of these deflection functions.

A semiquantal theory based on a binary-encounter approach is applied to the examination of the ionization of $\mathrm{He}\left(1\mathrm{}{s}^2\right)$ and ${\mathrm{Li}}^{+}\left(1\mathrm{}{s}^2\right)$ by the impact of hydrogen atoms in their ground state with incident energy $E$ above 10 keV. Simultaneous excitations of the projectile atom are explicitly acknowledged. The use of Born's approximation for electron-atom elastic and inelastic-scattering results in satisfactory agreement with the Born cross sections for atom-atom collisions.

The Euler equations for a classical asymmetrical rotor possessing a permanent electric-dipole moment and subject to a radiative-damping torque have been solved using a multi-time-scale approximation. The approximation exploits the fact that the radiative relaxation time is much longer than a rotational period. Using this method, the infrared radiation emitted from a highly excited rotating water molecule is calculated. The power as a function of time and the total energy emitted in a broadband are displayed.

The electron-excitation cross sections of the $3{}_{}{}^2{}_{}{}^{}P$, $3{}_{}{}^2{}_{}{}^{}D$, $4{}_{}{}^2{}_{}{}^{}S$, $4{}_{}{}^2{}_{}{}^{}P$, $4{}_{}{}^2{}_{}{}^{}D$, and $4{}_{}{}^2{}_{}{}^{}F$ states have been calculated at several incident energies between 4 and 24 eV by using the method of close coupling. Three different sets of calculations in which the wave functions of the electron-atom system are expanded by three states ($3s,3p,3d$), by seven states ($3s,3p,3d,4s,4p,4d,4f$), and by eight states ($3s,3p,3d,4s,4p,4d,4f,5p$) of the target atom, have been performed in order to investigate how the cross sections are influenced by the indirect coupling of the ground state to the final state through the intermediate ones. The $3{}_{}{}^2{}_{}{}^{}D$ cross sections are found to be about 30% higher than the values obtained by the Born approximation and by the scheme of $3s-3d$ two-state close coupling. The strong coupling of $3s$ with $3p$ and of $3d$ with $3p$ provides an indirect coupling between $3s$ and $3d$ which is mainly responsible for the large increase of the $3{}_{}{}^2{}_{}{}^{}D$ cross sections over the Born-approximation values. A similar kind of increase in the cross sections is also observed for the $4{}_{}{}^2{}_{}{}^{}D$ state owing to the indirect coupling through the intermediate $3p$ and $4p$ states. Inclusion of the intermediate states $3{}_{}{}^2{}_{}{}^{}D$, $4{}_{}{}^2{}_{}{}^{}D$, and $4{}_{}{}^2{}_{}{}^{}S$ in the close-coupling calculation likewise affects considerably the $3{}_{}{}^2{}_{}{}^{}P$ and $4{}_{}{}^2{}_{}{}^{}P$ cross sections. The effect of indirect coupling is most pronounced in the $4{}_{}{}^2{}_{}{}^{}F$ cross sections (ranging from a fourfold to a tenfold increase over the Born approximation), because the direct coupling between $3s$ and $4f$ is weak and of rather short range so that the major contribution to the cross sections arises from the indirect part. Comparisons of the theoretical cross sections with the experimental values are made.

The generalized random-phase approximation (GRPA) developed for electron-scattering problems is applied to the photoionization of electrons from atoms. In contrast to some other attempts to apply many-body techniques to photoionization problems, we concentrate on the generalized linear-response function of the ion, not the atom. This allows us to incorporate both the change in the effective charge seen by the outgoing electron during the photoejection process and the core polarization of the inner electrons in a rigorous manner. The derivation leads quite naturally to a formally exact one-electron theory of photoionization. In addition, corrections to the one-particle picture can be generated in a natural way. We conclude by examining some of the lower-order corrections to this one-electron model.

Presented here are experimental results of a study of the systematics of electron emission from discrete states of He and ${\mathrm{He}}^{-}$ as produced by ${\mathrm{H}}^{+}$, $\mathrm{H}_2^{}{}_{}{}^{+}$, ${\mathrm{He}}^{+}$, and He impacts. The results were obtained by energy analysis of the electrons emitted at angles of 10° to 160°. Projectile energies ranged from 20 to 150 keV. Differential and integrated cross sections are presented for emission of electrons from the $2s^2\left({}_{}{}^1{}_{}{}^{}S\right)$, $2s2p\left({}_{}{}^3{}_{}{}^{}P\right)$, the sum of the $2p^2\left({}_{}{}^1{}_{}{}^{}D\right)$ and $2s2p\left({}_{}{}^1{}_{}{}^{}P\right)$ autoionizing levels of He, and the $1s2s^2\left({}_{}{}^2{}_{}{}^{}S\right)$ autodetaching level of ${\mathrm{He}}^{-}$. The $2s^2\left({}_{}{}^1{}_{}{}^{}S\right)$ cross section is nearly isotropic, while the $2s2p\left({}_{}{}^3{}_{}{}^{}P\right)$ and $2p^2\left({}_{}{}^1{}_{}{}^{}D\right)+2s2p\left({}_{}{}^1{}_{}{}^{}P\right)$ cross sections are in general anisotropic. The ratios of the ${}_{}{}^3{}_{}{}^{}P$ to the ${}_{}{}^1{}_{}{}^{}S$ cross sections follow an approximate $A+B{cos}^2\theta$ form. The peak arising from the ${\mathrm{He}}^{-}$ level has an asymmetric profile with a positive $q$ value which increases as the projectile energy decreases.

The characteristic $L$ x-rays of Au, produced by 0.5-30-MeV proton beams on a thin Au target have been observed with a Si(Li) detector. Total $L$ x-ray production cross sections derived from these measurements are in good agreement with presently available theoretical calculations. However, theoretical predictions of $\frac{L\alpha }{L\beta }$ and $\frac{L\alpha }{L\gamma }$ ratios and centroid energies of the $L\beta$ and $L\gamma$ lines as functions of proton energy show that a consistent quantum-mechanical treatment of $L$-shell ionization gives considerably better agreement with experimental results than the semiclassical or classical theories of inner-shell ionization.

The positron-hydrogen collision problem has been investigated by the Faddeev formalism as used by Sloan and Moore. The cross sections for the elastic scattering and the positronium formation have been calculated above the positronium-formation threshold for the incident positron energy up to 1.36 keV, and the results have been compared with those of other theoretical calculations. Appreciable differences have been found between the present results for the elastic-scattering cross sections and the corresponding results obtained by the first-order Born approximation at energies as high as the order of keV. The proton-positronium elastic-scattering cross sections are also reported. These cross sections which vanish in the first-order Born approximation are found to be significant at low incident proton energies.

A stationary variational functional for the $T$ matrix that uses trial $T$ matrices rather than trial wave functions is discussed. Taking a trial $T$ matrix expressed as a general linear combination of matrices leads to a Fredholm integral equation of the first kind for the coefficient vector. The special case of a trial function having the same form as the Born series, except with variable coefficients, is treated in detail. Requiring the functional to be stationary with this trial form leads to the previously established result of Padé approximants to the scattering amplitude. Approximate techniques are used to evaluate the high-order Born integrals, and the behavior of the Padé approximants and the Born series is investigated for a Yukawa potential. An upper bound on the series is used to estimate its radius of convergence as a function of energy and potential strength. The variational calculations converge rapidly even for cases where the Born series diverges.

Proton-impact ionization and dissociation of the $\mathrm{H}_2^{}{}_{}{}^{+}$ molecule is studied within the frame-work of the classical binary-encounter approximation. The effect of the Coulomb field of the ion is considered. A quantal momentum distribution is used for the bound electron. The $R$ dependence of the cross section has been studied and an average cross section for two initial vibrational states ($\nu =0\mathrm{}$ and 3) is obtained. It is observed that the initial vibrational state has a marked influence on the total cross section.

The dissociative attachment cross section for ${\mathrm{O}}^{-}$ from C${\mathrm{O}}_2$ in the neighborhood of 4.4 eV is examined with high resolution, and structure in this cross section is observed. We interpret this structure as an indication that vibrationally excited states of CO are produced in the reaction $e+{\mathrm{CO}}_2\to \mathrm{O}+\mathrm{CO}$. The magnitude of the cross section for the production of CO for individual states ($\nu =0\mathrm{}-3$) is estimated. The peak magnitudes of the dissociative attachment cross sections for production of CO in the vibrational states $\nu =0,1,2\mathrm{}$, and 3 are in the ratio of approximately 1:0.63:0.40:0.10. The threshold region for the dissociative attachment cross section in C${\mathrm{O}}_2$ is examined in the temperature range (200-300)° K, and it is found that this region can be described by a nonvertical onset and by the contribution of the bending mode to the attachment process.

The associative detachment reactions of ${\mathrm{O}}^{-}$ with CO, ${\mathrm{H}}_2$, and ${\mathrm{O}}_2$ are studied experimentally using an ion beam (0-10 eV) impinging on a gas-filled chamber. The resultant electrons are energy analyzed using retarding potentials. At low ion energy, cross sections for total electron detachment for the reactions of ${\mathrm{O}}^{-}$ with CO and ${\mathrm{H}}_2$ vary as the inverse of the relative velocity. At higher energies, the cross sections show a broad peak. We interpret this shape in terms of the potential-energy curves of the compound states. The energy distributions for the electrons resulting from the reactions of ${\mathrm{O}}^{-}$ with CO and ${\mathrm{H}}_2$ exhibit peaks at low energy corresponding to the excitation of high vibrational and rotational states of the resultant triatomic molecules (C${\mathrm{O}}_2$, ${\mathrm{H}}_2$O). Progressions observed in these distributions have spacings corresponding to the preferential excitation of the bending modes of the triatomic molecules. The cross section for total electron detachment for the reaction of ${\mathrm{O}}^{-}$ with ${\mathrm{O}}_2$ exhibits a threshold near 0.7 eV and rises linearly at higher energy.

Oscillator strengths and the photoionization cross section for the ground state of cesium are computed using a semiempirical model potential involving two adjustable parameters and based only on the lowest few spectroscopic term values. The spin-orbit interaction is included in the model potential, and the effects of core polarization are explicitly taken into account in both the model potential and the dipole transition matrix element. The doublet-line-strength ratios for discrete transitions are in good agreement with Agnew's measured values, and no support is given other indications that the line strength for $6s\frac{1}{2}-\mathrm{np}\frac{1}{2}$ is vanishingly small somewhere in the region $n=10\mathrm{}-15$. Good agreement with two recent measurements of the spin-orbit effect in photoionization is also obtained. The oscillator strengths and photoionization cross section are significantly lower than the measured values of Agnew, and Marr and Creek, respectively, but the total atomic polarizability is in excellent agreement with a recent measurement.

A distorted-wave formulation with exchange is given for the electron-impact excitation of atoms from ${\left(n_0{l}_0\right)}^N$ to ${\left(n_0{l}_0\right)}^{N-1\mathrm{}}\mathrm{nl}$ configurations using the $\mathrm{LS}$-coupling scheme. Phenomenologically determined independent-particle models and distorted-wave potentials are utilized to compute angular distributions and integrated cross sections for $2p\to 3s,3p$, and $4p$ excitations of atomic oxygen over wide ranges of energy and momentum transfer. The results are compared with the Born-approximation limit as well as the experimental integrated cross section of Stone and Zipf.

A semiclassical limit, defined in terms of large mass and energy at fixed arbitrary collision velocity, is shown to be a simple formal prescription for obtaining a quantum treatment of the impact-parameter method and the eikonal approximation. In particular, for atomatom collisions, the resultant approximation is emphasized to be a proper strong-coupling equation for inelastic processes, as opposed to the adiabatic result of a large-mass limit at fixed energy.

Self-diffusion coefficients of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$, and ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ have been measured in 1-20-MPM (100×moles metal/total of moles metal and moles ammonia) solutions of lithium ammonia at 223 and 233 K and in 2-15.5-MPM solutions of sodium ammonia at 233 K by the NMR spin-echo pulsed-magnetic-field-gradient technique. In addition, the temperature dependences of the self-diffusion coefficients were measured for seven representative concentrations of lithium ammonia below 240 K. The data indicate that the lithium and sodium ions are solvated by four ammonia molecules over the time scale of molecular diffusion. The concentration dependence of the self-diffusion coefficients of the metal-ion complexes and of the free-ammonia molecules is found to be consistent, evaluated by the Stokes-Einstein relation, with the available viscosity data. The melting-point self-diffusion coefficient and the temperature dependence of 20-MPM lithium ammonia are fitted to the Ascarelli-Paskin and Cohen-Turnbull diffusion models for a reasonable choice of packing fraction.

The uniform WKB theory of inelastic collisions is discussed further and applied to a semi-classical analysis of the ${\mathrm{He}}^{+}$-Ne inelastic collisions [${\mathrm{He}}^{+}+\mathrm{Ne}\left(2\mathrm{}{p}^6\right)\to {\mathrm{He}}^{+}+{\mathrm{Ne}}^{*}\left(2\mathrm{}{p}^{5}3s\right)$] at $E=70.9\mathrm{}$ eV. The uniform WKB differential cross section of the inelastic scattering is compared with that of the Landau—Zener—Stückelburg theory of inelastic collisions. The result of comparisons indicates that the uniform WKB theory is more reliable than the Landau—Zener—Stückelberg theory and the distorted-wave-Born-approximation theory.

The theory and application of the matrix-shape (MS) approach is investigated for elastic scattering. Various aspects of the method, such as the choice of appropriate variables, the choice of basis-set functions as representations of the $T$ matrix, and the use of a MS fit to the potential matrix that allows $V{G}_0^{+}T$-type integrals to be performed analytically, are considered. The method is applied to three-dimensional elastic scattering to ascertain if, on this widely studied problem, the MS approach can in fact produce the essential physics. Numerical calculations are presented to illustrate that reasonable results can be achieved. The numerical results were obtained using two special cases of the method of weighted residuals, which can be used with the MS approach to solve the Lippmann—Schwinger equation for $T$. The use of the MS approach in conjunction with variational principles is also discussed.

Laser-induced fluorescence line narrowing has been studied in a series of samples of glass: Nd. The features of the nonresonant-excitation technique are described, and the results are discussed in terms of the known spectroscopic properties of the glass: Nd system. The concentration and temperature dependence of the line narrowing have been studied, and the spectral diffusion that is observed is analyzed in terms of resonant ion-ion energy transfer.

A variational wave function is constructed for the ground state of ${\mathrm{He}}^3$ and ${\mathrm{He}}^4$ films adsorbed on graphite when the density is near that of a completed monolayer. By using this wave function, the density of the completed monolayer is calculated while the exchange effects and Debye temperatures are estimated. Comparisons with experiments are made. The pair-distribution function and the corresponding structure factor and Debye-Waller parameter are predicted.