Precise calculations of the energy levels and fine structure of antiprotonic atoms, in which the normal and anomalous magnetic moments of the antiproton are treated on an equal basis and vacuum polarization and relativistic recoil corrections are included, are presented. The results are applied to measurements of the antiproton mass and anomalous magnetic moment with the use of antiprotonic atoms.

This paper presents the first complete topological description of the electronic-probability current-density field in molecules under an external homogeneous magnetic field. The analysis is general, applying both to the many-electron current density and to its one electron (orbital) components. The singular lines of the vector field form a stagnation graph which is the skeleton of the qualitative theory presented here. This graph may be disconnected, with one connected part playing a leading role in the description. Other secondary connected parts are encased into topologically spherical separatrices defined by two isolated singular points. This is one of the types of separatrices which are introduced here. The other one is defined by saddle singular lines and encases the axial vortices which are associated with the vortex stagnation lines. The vertices of the stagnation graph are critical points of the current-density field, points where the stagnation lines may branch out according to an index theorem that is proved here. The basic units in this qualitative description of the current field are axial or toroidal vortices. Each vortex is a whirlpool of electronic-charge probability flowing around a vortex stagnation line and encased into a closed separatrix. Vortices may exist inside other vortices but separatrices cannot cross one another. Saddle stagnation lines belong to the boundary of four or more axial vortices.

A study has been made of the photodissociation of the molecules NaI, TlI, Hg${\mathrm{Br}}_2$, and Pb${\mathrm{Br}}_2$ by polarized 193-nm ArF laser light. A significant degree of polarized fluorescence was measured from excited photoproducts Tl and HgBr. No polarization was observed in the Na and Pb fluorescence, while the Hg polarization was small. For Tl the spatial anisotropy of the dissociated atoms was also measured by atomic absorption, yielding an asymmetry parameter value of $\beta =1.2\mathrm{}$. The best current explanation for the polarized Hg and Tl emission is that fine-structure and hyperfine-structure magnetic substates, respectively, are preferentially populated by the dissociation process.

The speed of tunneling of the electromagnetic wave packets propagating in nondispersive dielectric media is analyzed on the basis of Maxwell's equations. It is shown that under certain conditions this speed can exceed the speed of light in vacuum.

A relativistic multichannel quantum-defect theory is formulated in the same way as in the nonrelativistic theory of Seaton. The solutions to the radial Dirac-Coulomb equations are reviewed in complex values of energy. The simple-model problem with finite-range potentials is used to clarify the scattering matrix and the reactance $K$ matrix. The close-coupling approximation is discussed for real atomic systems.

We report the determination of the absolute rate constant of ${\mathrm{Na}}_2^{+}$ production by associative ionization collisions between crossed beams of Na $3{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ atoms. New measurement techniques greatly improve the accuracy of rate-constant determinations in crossed-beam experiments. We find the rate constant to be (1.8±0.7)×${10}^{-11\mathrm{}}$ ${\mathrm{cm}}^3$${\sec }^{-1\mathrm{}}$. This value is appreciably larger than many of those previously reported.

We illustrate the possibility for calculation of bremsstrahlung tip angular destributions and polarization correlations from corresponding photoeffect results with an extension of the method for connecting bremsstrahlung tip and direct-radiative-recombination (DRR) cross sections developed by Lee and Pratt. The agreement between results obtained with this method and results from our numerical partial-wave calculations is, in general, satisfactory. We note features of the distributions and correlations, and once again point out the inadequacies of the nonrelativistic dipole approximation for the evaluation of bremsstrahlung or DRR angular distributions.

The energy-loss distribution for pions and protons, with momenta between 0.7 and 115 GeV/c, has been measured in an ion-implanted detector of 300 μm thickness. The data are well described by an empirical energy-loss distribution.

A polarization potential ($V_{\mathrm{pol}}$) for $e$-${\mathrm{N}}_2$ collisions is calculated by the generalization of the static part of the method of polarized orbitals to molecular targets. Partial differential equations (PDE) are derived for polarized orbitals, which are functions of the distance ($r$) from the molecular center and angle ($\theta$) from the molecular axis. The equations are solved with the use of the noniterative PDE technique. From the polarized orbitals a polarization potential can be constructed whose $r$ and $\theta$ dependence is found to be significantly different from the well-known phenomenological one. The two potentials are further compared by carrying out limited hybrid-theory scattering calculations. Only those scattering results based on the calculated $V_{\mathrm{pol}}$ are in satisfactory accord with experiment.

Molecular-structure calculations have been performed to obtain the adiabatic potentials for ground state and numerous excited states of alkali-metal—He systems. They use $l$-dependent pseudopotentials defined from spectroscopy data or scattering data to describe the $e^{-}-M^{+}$ and $e^{-}$-He interactions (where $M$ is any alkali-metal atom). Standard variational calculations are made, and a large basis set of Slater-type orbitals is used in order to ensure accuracy and stability of the results. Our results are discussed along with comparisons with other theoretical and experimental data. The overall agreement which has been obtained with all available experimental data indicates that significant improvements in the calculation of the $M$-He adiabatic potentials have been achieved by using an $l$-dependent pseudopotential technique.

The contribution of the spin-orbit interaction to the rotationally inelastic scattering of neutrons from a closed-shell diatomic molecule is studied. For small momentum transfer and $\Delta J=\pm 1$ rotational transitions, the first Born-approximation amplitude depends approximately on the factor $\Delta \omega D{q}^{-1\mathrm{}}$ (in atomic units), where $\Delta \omega$ is the energy transferred, $D$ is the permanent dipole moment of the target, and $q$ is the momentum transferred. The dependence on $\Delta \omega D$ is the same as that of the coefficient of absorption of long-wavelength radiation, and the dependence on $q^{-1\mathrm{}}$ is characteristic of particle scattering in a dipole potential. Essentially $\Delta J=\pm 1$ cross sections are enhanced because rotational energy transfer can occur over appreciable target-neutron distances. Thus the tiny rotational transition strength $\Delta \omega D$ is weighted by the large factor $q^{-1\mathrm{}}$. This means that a classical average of the cross section over molecular orientations cannot describe the physical process. The importance of this result to the theory of neutron-optical activity is discussed.

Electron emission following the ionization of projectile ions has been investigated systematically in collisions with ${\mathrm{Ne}}^{q+}$ and ${\mathrm{Ar}}^{q+}$ ions at several hundred MeV incident on different target gases. The projectile electrons are concentrated within one maximum, the electron-loss peak (ELP). The variation of the shape and intensity of the ELP with the projectile energy, its charge state, the observation angle, and the target gas has been measured. Theoretical predictions which are based on the binary-encounter approximation show, in general, good agreement with the experimental data. The contributions of the different subshells to the ELP are deduced. It is shown that electronic screening of the target nucleus plays an important role in the ionization process of the projectile ions.

Recommended angular and energy distributions of slow secondary electrons produced from helium by electron impact are presented in a compact table. The table lists coefficients for the Legendre polynomials from which all angular and energy distributions can be generated for scattering angles between 0° and 180°, secondary-electron energies between 0 and 40 eV, and incident-electron energies between 100 and 2000 eV. The distributions represent double-differential cross sections that are consistent with expected asymptotic behavior, angular symmetry, and integrated cross sections. These cross sections should be sufficiently reliable to serve as normalization standards for experiments on secondary-electron distributions.

Electron scattering from a potential in the presence of a classical, monochromatic, spatially homogeneous radiation field is considered. A coupled integral equations method is formulated to calculate the cross section for stimulated photon emission or absorption. This method is applicable for field strengths such that the difference between the instantaneous velocity and the cycle-average velocity of the electron is not too large. The method has been applied to the case of a separable potential, and some results are presented.

The theory of the energy loss of an ion with charge $Z_{1}e$ passing through an electron gas is considered. The term proportional to $Z_1^3$ in the expression for the stopping power of the medium is derived by taking a second functional derivative of the induced charge in the medium and is expressed as a product of three Green's functions. The actual evaluation is effected by separately treating the momentum transfer to distant and close collisions. Also, it is assumed that the Fermi energy $E_F$ is less than $\hslash {\omega }_p$, the plasmon energy of the medium. The contribution to the $Z_1^3$ term from distant collisions is similar to that obtained by others using an atomic model for the stopping medium if one replaces the atomic binding energy by $\hslash {\omega }_p$. The contribution from the region of close collisions is shown to be unimportant compared to that from distant collisions because screening of close collisions is expected to be negligible in the electron gas. This work will discuss related work by Lindhard and Esbensen, and by Arista, who arrive at different conclusions with respect to this impact-parameter dependence.

The theory of configuration interaction in molecules is extended to permit the simultaneous treatment of doubly excited electronic states and vibrationally excited Rydberg states which can decay by autoionization and predissociation. The method is applied to dissociative recombination and compared with the corresponding multichannel quantum-defect theory. Calculations using both techniques are reported for collisions of electrons of energy below 0.5 eV with ${\mathrm{H}}_2^{+}$ ions in the lowest three vibrational states. The Rydberg states lead to narrow structures in the cross sections, mostly in the form of dips. The cross section and recombination rate for ground-state ions are anomalously low, being smaller than those for $v=1\mathrm{} \mathrm{and} 2$ by a factor of ∼6.

Using the HFDHE2 He-He potential of Aziz et al. [J. Chem. Phys. 90, 4330 (1979)] with the Faddeev-Yakubovsky theory, we have calculated the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ atom-triatom scattering length and found it to be - 116 Å. We reduced the $s$-wave two-body $t$ matrix to a separable form through the unitary-pole approximation and did the same for the $s$-wave [3+1] and [2+2] subamplitudes with the energy-dependent-pole approximation in our work. Also, the binding energies of all the states in the trimer and tetramer, and the atom-diatom scattering length, already determined in our previous work with other potentials, were recalculated for the new interaction. We found an excited trimer bound state, apparently not an Efimov state, near the atom-diatom threshold and an atom-diatom scattering length of 195 Å. A feature of our results was the absence of an excited state in the tetramer, but in its place, was a resonancelike state which led to the large atom-triatom scattering length.

Distorted-wave cross sections are presented for the excitations of the $w{}_{}{}^1{}_{}{}^{}\Delta _u^{}{}_{}{}^{}$, $W{}_{}{}^3{}_{}{}^{}\Delta _u^{}{}_{}{}^{}$, $A{}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$, $b^{\prime }{}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$, and $c^{\prime }{}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ states of ${\mathrm{N}}_2$ by low-energy electron impact. The distorted waves are obtained in the static-exchange field of the ground electronic state. Differential and integral cross sections are presented from near threshold up to 60-eV impact. Comparison is made with available experimental data and with other calculations.

The origin of beam-foil convoy electrons has been a subject of many controversial interpretations and discussions. In this work, velocity distributions of electrons ejected into the forward direction from a carbon-foil target have been measured with incident proton beams of energies between 60 and 300 keV, and under the same experimental conditions as equivalent measurements recently performed in this laboratory with a He-gas target. Cusp widths are discussed as a function of projectile velocity and instrumental angular acceptance by taking fractional peak heights from the base line as well as by previously subtracting a background obtained by joining peak tails. It is concluded that neither of these procedures is valid. On the other hand, measured electron spectra can be well fitted in terms of a general parametric expression of the scattering amplitude for an electron transfer to the continuum process. The absence of a strong negative cusp skewness, as was observed with the gas target, hints in the direction of an electron loss rather than an electron capture to the continuum process. A significant background contribution that is absent for a single-collision electron transfer to the continuum process is interpreted as due to the emission of secondary electrons that are not correlated to the emerging projectiles.

The Glauber-type eikonal amplitude for a fixed molecular orientation is used in the framework of adiabatic approximation to compute pure elastic excitation ($J=1\mathrm{}\to J^{\prime }=1\mathrm{}$), rotational excitation ($J=1\mathrm{}\to J^{\prime }=3\mathrm{}$), and orientationally averaged elastic cross sections of the oxygen molecule in its ground electronic and vibrational states with the use of electrons as incident particles. Both differential and integral cross sections are reported at electron energies 20-200 eV. The effect of target polarization is included in the effective electron-molecule potential used, but that of electron exchange is neglected. The results are compared with the available experimental data and theoretical calculations of other workers. A comparative study of the molecules ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, and ${\mathrm{O}}_2$ as targets is made.