Angularly resolved Auger rates are investigated. The angular distributions of Auger electrons display a strong dependence on the final dicationic state which is created by the Auger process. The angular distributions show interference structures which can be related to the geometry of the molecule. Although there are presently no experimental data on angularly resolved Auger rates, we suppose that the angular distributions are measurable, e.g., by coincidence techniques.

(2+1) resonance-enhanced multiphoton-ionization photoelectron spectroscopy studies are reported for the metastable ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}_{\mathit{J}}^{\mathit{o}}$ and ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{\mathit{J}}^{\mathit{o}}$ nitrogen atomic species presumably produced by photodissociation of the ${\mathrm{N}}_3$(X ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$) radical. Two-photon transitions to a multitude of doublet Rydberg states of odd parity are observed in the wavelength range 225.5–294.5 nm. This comprehensive coverage follows all np Rydberg states from n=3 to the ground-state ionization limit ${(}^3$${\mathit{P}}_{0,1,2}^{\mathit{e}}$) with n=25 being the highest identifiable. Perturbations are observed around n=5 due to an interloping np Rydberg state (n=3) converging to the first excited ionic limit ${(}^1$${\mathit{D}}_2^{\mathit{e}}$). A limited multichannel-quantum-defect theory (MQDT) analysis was performed to estimate the composition of the wave functions in this bound-bound interaction. In addition, nf Rydberg states from n=4 to 10, and some other weaker quartet states, have also been identified; these, and higher np states (n>8) show a breakdown of LS coupling. Overall, a considerable number of new states have been identified. Photoelectron kinetic-energy scans give information on the ion state distributions from the branching ratios to the ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_{0,1,2}^{\mathit{e}}$ ground and the ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2^{\mathit{e}}$ and ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0^{\mathit{e}}$ excited states of ${\mathrm{N}}^{+}$; these can be compared to calculated values obtained from the MQDT analysis. Core- and non-core-preserving transitions are observed, and in one case almost complete state selection of excited ${(}^1$${\mathit{D}}_2^{\mathit{e}}$) nitrogen atomic ions is observed. Analysis of the Doppler profiles of the atomic transitions provides evidence for the mechanism which is at play in the formation of N metastable states.

Partial cross sections were measured for the ionization M+e→${\mathit{M}}^{\mathit{n}+}$+(n+1)e for M=Kr and Xe (n=1–6) as a function of electron energy (0–470 eV). The experiment is based on a crossed-beam time-of-flight mass spectrometer employing pulsed electron and atomic beams, and pulsed ion extraction. Cross sections for ${\mathrm{Kr}}^{5+}$, ${\mathrm{Kr}}^{6+}$, and ${\mathrm{Xe}}^{6+}$ have not been previously measured over this energy range. The cross sections reported for the remaining ions considerably narrow the uncertainty of previous measurements. The source of discrepancy among recent work appears to be due to improper account of detector-gain effects. The ionization onsets are fitted to threshold power-law expressions to derive ionization potentials.

A classical model of two interacting dielectric spheres (DS) in an electric field is proposed to calculate the trace and anisotropy of the polarizability tensor of a pair of isotropic molecules. The case of noble gases is treated. It is shown that the dielectric-sphere-couple anisotropy is quite close to the dipole-induced-dipole (DID) anisotropy, while the DS trace is significantly greater than the DID trace, even at long distances between the interacting spheres. These results are interpreted as being due to the non-negligible multipolar contributions to the trace. To examine the validity of the model, its predictions are compared with results of experiments (trace and anisotropy are responsible for many collision-induced optical phenomena or properties) and of self-consistent-field calculations.

We have studied ionization for the collision system ${\mathrm{H}}^{+}$+He at 300 keV in a coincidence measurement, using a newly developed recoil spectrometer, which allows us to measure the charge state of the recoil ion without affecting the emitted electrons. Doubly differential probabilities [per energy interval and solid angle of the emitted electron(s) per scattered projectile at a fixed impact parameter] are determined as a function of the charge state of the He recoil ion. Comparison is made with results of different classical and quantum-mechanical collision theories. Strong deviations are found between the measured data and the predictions of the independent-particle model.

Positrons from a radioactive source are slowed to electron-volt energies and accumulated and stored in a trap which uses a magnetic field for radial confinement and an electrostatic well for axial confinement. The positrons lose energy and become trapped through inelastic collisions with nitrogen molecules introduced into the trap for this purpose. The trap has three stages with progressively lower nitrogen pressure. It is found that the trapping in each stage is due primarily to electronic excitation of the nitrogen molecules, with the energy loss being approximately 9 eV per collision. Positronium formation is believed to be the dominant loss mechanism during the trapping process. Trapping efficiencies of greater than 25% have been achieved. Using a 150-mCi ${}_{}{}^{22}{}_{}{}^{}\mathrm{Na}$ source, a maximum stored number of ∼1×${10}^7$ positrons have been stored with a lifetime of 40 s, limited by the annihilation on the nitrogen gas at a pressure of 2×${10}^{\mathrm{-}6}$ Torr. The positrons cool to room temperature in a few seconds via rotational and momentum transfer collisions with the nitrogen.

Using various recently proposed interaction potentials for the ${\mathrm{Li}}^{+}$-He system, elaborate calculations of the mobility, longitudinal, and transverse diffusion coefficients of ${\mathrm{Li}}^{+}$ swarms in helium have been made by high-speed Monte Carlo simulations (MCS’s). In addition, the transverse diffusion coefficients for this ion–neutral-atom pair have been experimentally measured with total errors of ±3%. The close agreement of the present experimental results with those of Skullerud, Eide, and Stefansson [J. Phys. D 19, 197 (1986)] as well as the faithful MCS reproduction of all three transport coefficients using the interaction potential proposed by Larsen et al. [J. Phys. B 21, 2519 (1988)] over the entire range of E/N (electric field to neutral-particle number density ratio) studied not only provides confirmation of their transport coefficient values, but also lends strong support for their proposed interaction potential. In comparison, the more recent potentials of Ahlrichs et al. [J. Chem. Phys. 88, 6290 (1988)] and of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] did not reproduce the experimental data quite as well. As a benchmark the MCS calculations have also provided evidence of the accuracy of the Kramers-Moyal expansion method in calculating the transport coefficients.

A method for obtaining the exchange scattering amplitude for electron-impact ionization of atomic hydrogen in the eikonal approximation is developed. The expression for the eikonal amplitude in the present case turns out to be a two-dimensional integral which can be evaluated numerically with convenience. This exchange amplitude can be combined with the corresponding direct amplitude to calculate both differential and total cross sections for electron-impact ionization of hydrogen atoms. We present numerical results for triply differential cross sections (TDCS) for the H(e,2e)${\mathrm{H}}^{+}$ process for incident energies of 150 and 250 eV. A comparison is made of the present TDCS with the corresponding results of other calculations and experiment.

We examine the physics behind the continued success of the independent-processes and isolated-resonance approximations in predicting the high-resolution recombination cross sections observed in the current generation of electron-ion experiments. First-step extensions of theory to include the effects of radiative-dielectronic recombination interference, overlapping-resonance structures, and scattering-channel coupling are shown to be relatively small for these recombination experiments.

Energies and absolute cross sections for dielectronic recombination of lithiumlike ${\mathrm{Cu}}^{26+}$ via ΔN=0 and ΔN=1 resonances have been measured at the Heidelberg heavy-ion storage ring TSR employing the electron cooler as a target of free electrons. In particular, resonances associated with 2s→2p and 2s→3l excitations have been observed. Resonances due to the doubly excited states 1${\mathit{s}}^2$2${\mathit{p}}_{1/2}$nl and 1${\mathit{s}}^2$2${\mathit{p}}_{3/2}$nl could be resolved up to n=30. Fine-structure components are partly resolved for the 1${\mathit{s}}^2$3l3l’ resonances. The results are compared with theoretical calculations and show good agreement.

Nuclear fusion yields for the secondary reaction D+D have been measured for carbon-atom anions and carbon-cluster anions incident on a deuterated polyethylene target for atom and cluster energies up to 324 keV. Comparison of the cluster- and atom-anion fusion yields per carbon at the same bombarding energy per carbon show no evidence of a collective enhancement for clusters as large as ${\mathrm{C}}_{19}$. The absolute yields can be reproduced by a knock-on model. An upper limit to the fusion yield for ${\mathrm{C}}_7$${\mathrm{D}}_7$${\mathrm{SO}}_3^{\mathrm{-}}$ bombardment has also been determined.

A theoretical investigation based on the linear dielectric formalism is presented of the stopping of large clusters in metals at velocities above the Fermi velocity. Calculations are carried out for hydrogen clusters of 4, 13, and 100 ${\mathrm{H}}_2$ molecules stopping in aluminum. Emphasis is placed on the influence of the internal cluster structure, which enters in the present description via the pair-correlation function for the relative positions of nuclei. The target properties are modeled by Lindhard’s dielectric function for a free-electron gas. Interference effects with respect to both collective and individual excitations are quantified separately for intra- and intermolecular terms, and are evaluated as a function of cluster velocity. Effects of short-range order, in particular the importance of an exclusion volume around each molecule, are clearly visible. The results indicate, however, that beyond the nearest neighbor the detailed molecular arrangement has only little influence on the stopping power for the clusters studied. The partitioning of contributions due to close and distant collisions, as it is known for the stopping of point charges, is found to be substantially different in the case of cluster projectiles. The effect of Coulomb repulsion is commented upon.

We present an analysis of the stopping power for helium in silicon taking into account the contributions due to different charge states. Our calculations include effects due to the nonuniformity of the target valence-electron density along specific crystallographic directions as well as the electron density of the projectile. In the present work attention is restricted to projectile velocities greater than or equal to the Bohr velocity in order to compare with existing experimental data. The method employs a dielectric-response formalism taken in the random-phase approximation coupled with energy-dependent population factors for the different charge states. It is demonstrated that the total stopping power obtained in the present work shows reasonable agreement with experiment.

For the calculation of stopping power and ranges with the method suggested by Bethe, functions expressing the binding of the electrons in the atoms (‘‘shell corrections’’) are needed. Here, shell corrections calculated with hydrogenic wave functions have been employed. By using experimental atomic energy levels as parameters for them, I have found good agreement between experimental and calculated values of stopping power for elements with atomic number Z>56. Only for the mean ionization energy I there was no simple relation to atomic properties, and a considerable dependence of the Bloch parameter b=I/Z on Z has been found. Calculated values of stopping power and ranges agree with experimental values for protons with kinetic energies T above 0.5 MeV, for ions (with z protons and M≤40 nucleons) above T/M∼(z-1.5) MeV, well within the uncertainty of the experiments, but an approximately 1% discrepancy for several hundred MeV protons remains.

The hyperfine structures of six metastable levels arising from the 3${\mathit{d}}^2$4s and 3${\mathit{d}}^3$ configurations in ${}_{}{}^{49}{}_{}{}^{}\mathrm{i}$ have been measured with high precision using the laser-rf double-resonance technique in a collinear laser–ion-beam geometry. The hfs constants A and B were determined to about 4 and 43 kHz, respectively. Less precise results are also reported for the 2${\mathit{p}}_{1/2}$ level of the 3${\mathit{d}}^3$ configuration and for five upper levels in the 3${\mathit{d}}^2$4p configuration. For these states, the optical spectra had Doppler widths of about 40 MHz, leading to A values determined to about 1 MHz. The results are compared with the presently available Hartree-Fock (HF) calculations. Good agreement is obtained with the HF results only in some cases. Substantial corrections due to many-body interactions and relativistic effects are required for other cases.

The spectral line shapes for the HD rotational spectra perturbed by He and Ar gases, which show interference between allowed and collisionally induced dipole transitions, are calculated including the effects of inelastic rotational collisions. The general parametrization of the line shape, including inelastic collisions, requires six independent real parameters as opposed to four in the theory of Herman, Tipping, and Poll [Phys. Rev. A 20, 2006 (1979)]. Semiclassical calculations based on classical trajectories indicate the importance of the inelastic effects and show qualitative agreement with the experimental parameters. However, it is clear that a full explanation of experimental data will eventually require a full quantum treatment.

We present results for the partial and total widths, with interchannel and intrachannel coupling included, of the 1s(nl${)}^2$ ${}_{}{}^2{}_{}{}^{}$S resonances of ${\mathrm{He}}^{\mathrm{-}}$, n=3 and 4. These are obtained by solving the corresponding state-specific complex eigenvalue Schrödinger equations and subsequently using simple formulas. A number of conclusions are drawn as to the wave-function characteristics and the distribution of the autoionization rates. The computations include the self-consistent interactions between the core and the valence electrons, localized valence correlations, and interactions among all the open channels with helium 1sNl ${}_{}{}^{3,1}{}_{}{}^{}$L, l=0,1,2 cores. These prototypical calculations can be carried out in larger systems as well, since the structure of the theory is such that it allows the quantitative treatments of multichannel dynamics in arbitrary polyelectronic atoms. For the total widths, comparison is made with a previous 19-state R-matrix calculation and with measurements.

The mechanism of reactive processes in binary atomic encounters is investigated by employing a Rydberg atom as one of the reactants. This permits isolation of the excited valence electron so that its role in effecting the heavy-body process can be assessed. Penning ionization by a Rydberg atom, which is studied as an example of a reactive process, is shown to have a cross section significantly higher than might be inferred solely on the basis of overlap of the atomic wave functions of the ionic Rydberg core and the collision partner. A model to describe these reactive processes in which the nearly isolated Rydberg electron polarizes, and is therefore attracted by, the neutral ground-state reactant is proposed. This attraction occurs at an internuclear separation greater than that at which the ionic core of the Rydberg atom can substantially polarize the neutral atom but polarization of the neutral atom by the Rydberg electron leads to a transitory negative ion and concomitant Coulomb attraction to the ionic core. This Coulomb attraction thus leads to cross sections that are higher than would be calculated solely on the basis of atomic overlap.

Collective emission in a resonant cavity was observed between high-lying levels in Sr and Ba. These transitions react very sensitively to a static external electric field. The square root of the maximum of the intensity of the superfluorescent pulse decreases linearly with the second power of the electric field strength. The behavior of the maximum of the intensity, of the characteristic superfluorescent time, and of the delay time of the superfluorescent pulse was described in the framework of modified Maxwell-Bloch equations and explained by a change of the characteristic time constant of the superfluorescent pulse.

The energy values of the ground state and the low excited 2p(m=0) state of the hydrogen atom in a uniform magnetic field of arbitrary strength (up to 4.7×${10}^8$ T) have been calculated by using B-spline basis sets. The results are in good agreement with other theoretical calculations. It appears that B splines as basis functions are quite powerful in treating the problem of the hydrogen atom in an arbitrary magnetic field, especially in the transition region between low and high strength. It is also possible to extend this method to analyze general two-dimensional problems.