Computer simulation with the marlowe program is used to study the relative contributions of symmetrical and nonsymmetrical collisions to the Auger $L_{23}$ emission from an aluminum solid target irradiated by low- (5 keV) and high- (50 keV) energy argon ions. The inner-shell ionization process is considered to take place when the distance of closest approach between two collision partners gets smaller than a certain threshold distance which does not have to be the same in both symmetrical (Al-Al) and asymmetrical (Ar-Al) collisions. After cross checking the emission threshold measurements, the theoretical and experimental estimates of ionization thresholds in gases, absolute Auger yield measurements, and computer simulations using the ionization threshold as a parameter, it was found that the threshold distances for the symmetrical and asymmetrical collisions are 0.36 and 0.44 Å, respectively. The relative contribution to Auger emission of both kinds of collisions was substantial, both with 5 and 50 keV incident energy.

New measurements of total cross sections for single ionization of ${\mathrm{O}}^{5+}$ by electron impact are reported in the energy range 120–580 eV. The improved experimental accuracy reveals the structure of the inner-shell excitation-autoionization threshold. Comparison with distorted-wave calculations for direct ionization shows good overall agreement, but up to 9% difference in the shape for direct ionization in the energy region below the onset of 1s-nl excitation-autoionization. An effort was made to measure structure in the cross section due to resonant-excitation–auto-double-ionization which was suggested by earlier measurements. No clear evidence of these processes is observed, and their contribution to the total single-ionization cross section is determined to be less than ${10}^{\mathrm{-}20}$ ${\mathrm{cm}}^2$.

Experimental details are presented for the measurement of the effects of extrinsic electric fields on cross sections and Rydberg product-state distributions for dielectronic recombination of ${\mathrm{Mg}}^{+}$ with electrons. A new type of Rydberg state detector is described. Experimental results for dielectronic recombination in the presence of fields are presented for three field values, and these results are compared with theoretical calculations.

We have measured the electric field dependence of electron-ion recombination in liquid argon and xenon. The observed relationship is incompatible with Onsager’s geminate theory [Phys. Rev. 54, 554 (1938)] of recombination so we have developed a new, single-parameter model to describe the data. The model is based on realistic assumptions about liquid argon and xenon and yields a simple, analytic result. This work is part of a program to build a high-resolution liquid-xenon detector.

A very accurate method is applied, within the theoretical framework of the scattering close-coupling equations, to treat rotational predissociation processes in the He-CO van der Waals molecule. The method was already employed successfully to study vibrational predissociation of the He-${\mathrm{I}}_2^{\mathrm{*}}$ complexes and shows in the present case significant differences with several approximate methods used to estimate resonance positions. The physical implications of such differences are analyzed and discussed.

Differential cross sections have been calculated for electron transfer and elastic scattering in collisions between α particles and hydrogen atoms at α-particle energies from 1 to 70 keV. Differential cross sections for lower individual principal quantum numbers have also been determined. The electronic transition amplitudes in the eikonal equations for the scattering amplitudes were obtained by several coupled-molecular-state calculations: perturbed-stationary-state calculations with 2–22 states neglecting translational factors and the origin taken to be on the proton, and calculations with 4–10 states including plane-wave translational factors. The sensitivity of the differential cross sections to the size and type of basis is discussed, and a comparison is made with the two sets of theoretical results available at one energy. The qualitative validity of a simple semiclassical model at larger angles is shown; diffraction is shown to be limited to rather small angles.

We have measured the null positions in the third-order susceptibility for two-photon resonant (6 ${}_{}{}^1{}_{}{}^{}7$ ${}_{}{}^1{}_{}{}^{}$,3S) sum-frequency mixing in atomic mercury. In addition, we have made measurements of some 7S-nP oscillator strengths using a fluorescence-dip technique. Combined with earlier results we are able to obtain a set of 7S-nP (n=7–13) oscillator strengths which gives a good description of the third-order susceptibility. The uncertainty in the 7S-nP oscillator strengths is typically 35–50%. The absolute third-order susceptibility has been determined for energies less than 83 000 ${\mathrm{cm}}^{\mathrm{-}1}$ with an uncertainty of typically 20–30%.

We extend a previously developed formulation of QED based on self-energy to include the effect of perfectly conducting boundaries on spontaneous emission. The method is quite general and applicable to any quantum system and many boundary geometries. In particular, we compute the spontaneous emission rate of an atom near a conducting plate, inside a spherical cavity, and between parallel plates. We give general formulas and predict both enhanced and inhibited rates, in agreement with recent experiments.

Coincidence techniques have been employed in a detailed study of Compton scattering of 279.2-keV γ rays by K-shell electrons of tin and gold. Double-differential cross sections at four angles have been determined from about 30 keV to the kinematic limit. In the case of gold, clear evidence has been obtained for the infrared divergence effect predicted by Gavrila, and for Compton defects towards lower energies. The data obtained with tin do not show significant infrared divergence or Compton defects. The widths of the fully developed quasi-Compton peaks are about 85 and 55 keV in the case of gold and tin, respectively. A detailed investigation has been made of possible false coincidences arising from secondary processes. Energy-integrated single-differential cross sections have also been determined. Comparisons with other experimental data and with results of theoretical calculations have been presented. The experimental cross sections in the regime of low outgoing photon energies are much larger than nonrelativistic and relativistic theoretical predictions. The experimental data above about 100 keV are in much better agreement with the relativistic second-order S-matrix calculations of Whittingham, although at some angles deviations of about 30% are noticeable. The desirability of additional relativistic calculations and measurements with extremely thin targets has been pointed out.

Scattering geometries are represented by tensorial parameters classified according to symmetry under permutations P and Q: P changes a base set of wave functions into its Hermitian conjugate and Q interchanges the directions of incidence and scattering. These parameters interlink initial and final states of projectile and target, a linkage mediated by the angular momentum ${\mathrm{j}}_t$ transferred in the collision. Collision cross sections and expectation values of the observables are constructed as sums of geometrical parameters with different symmetries, weighted by dynamical parameters.

Wavelengths of the 3$p^6$3$d^9$ ${}^2$$D_J$–3$p^5$3$d^{10}$ ${}^2$$P_{J\mathcal{’}}$ transitions of the Co-like ions have been calculated for ions with atomic number 38≤Z≤92. The calculations were performed by using the multiconfiguration Dirac-Fock model with emphasis on the effects of electron correlation. The previously found discrepancies between theory and experiment have been removed due to the inclusion of the correlation effects in the theoretical calculations. A possible misidentification of the ${}_{}{}^2{}_{}{}^{}\mathrm{D}_{3/2}^{}{}_{}{}^{}$${\mathrm{-}}^2$${\mathrm{P}}_{1/2}$ transition for the ${\mathrm{Dy}}^{39+}$ ion is noted.

In weakly, off-resonantly pumped multilevel systems gain is usually observed at the transition frequencies (line-center lines) and at the pump-offset-dependent frequencies (Raman lines). Modes developing at these frequencies are subject to strong mutual competition due to several coupling mechanisms. A general six-level system is investigated in this paper. Line competition effects are studied in particular in the simplified basic four-level cases comprising parallel, cascade, and V-Λ subsystems. We predict the type of transitions which survive and ultimately remain active. A comparison with experimental results using far-infrared lasers is made.

An atomic electron excited to a coherent superposition of Rydberg states by a short laser pulse corresponds to a wave packet moving on a radial Kepler orbit. The dynamics of the motion of the wave packet can be observed in a two-photon process where a first laser pulse excites the wave packet, which at a later time is probed by a second pulse. In a many-electron atom a single valence electron excited to the Rydberg wave packet can exchange energy with the atomic ion core (electron correlation), whenever the Rydberg wave packet passes through the atomic core region. We can view this orbiting of the wave packet as a succession of below-threshold inelastic scattering events from the atomic ion core. A theory of two-photon absorption with time-delayed short laser pulses is developed which is based on a ‘‘smooth’’ multichannel quantum-defect Green function.

The probabilities of atomic excitation as a result of vacancy production in the 1s, 2s, and 2p shells have been calculated for elements with Z between 2 and 36 in the sudden approximation. Calculations were made with the Hartree-Fock-Slater wave functions. For rare gases, our results are in good agreement with those obtained by Carlson and Nestor [Phys. Rev. A 8, 2887 (1973)] with relativistic wave functions. The validity of the prediction of Carlson and Krause [Phys. Rev. 137, A1655 (1965)] by means of effective charge is discussed. Comparison with other theoretical calculations and the experimental data is made.

The negative ion ${\mathrm{PtN}}^{\mathrm{-}}$ has been studied by autodetachment spectroscopy in a coaxial laser-ion beam spectrometer. Sharp resonances were observed at photon energies near the photodetachment threshold, and the sharp structure could be assigned as ${}_{}{}^1{}_{}{}^{}\mathrm{}_{}^1{}_{}{}^{}$Σ(v=0) transition, followed by autodetachment of the ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }$ state. A rotational assignment was accomplished and the observed linewidths as a function of rotational energy elucidate the dynamics of the autodetachment process. Saturation of this transition and the resulting optical pumping dips give a unique method of determining the absolute cross section of the transition.

Resonant laser photoionization in hollow-cathode discharges has been detected and extensively studied. The direct charge production and the high electric field in the cathode dark space, that permits a very fast charge collection, enable us to detect a photoionization signal much faster than the conventional optogalvanic effect. A theoretical interpretation of the signal is given, supported by a very good agreement between numerical and experimental results. Detection limits of this technique are also evaluated.

We study the evolution in time and in one space coordinate of picosecond laser pulses interacting with a nonlinear medium modeled by three quantum states. This is done by solving numerically the equation of evolution of the density matrix elements together with the Maxwell equation. The nonperturbative treatment of the density matrix allows us to understand the contribution of the different optical transitions and populations to the pulse deformation during its propagation. We apply the model to CuCl where the quantum levels are the fundamental, the excitonic, and the biexcitonic states. Near the two-photon resonance, the pulse is strongly altered and the excitonic and biexcitonic levels show a population inversion. A modulation of the amplitude and a superbroadening of the phase occur during the propagation.

We use a three-state model for an atom or molecule in which two transitions are simultaneously driven by the oscillating electric fields of two laser beams. The amplitudes and detunings of the applied oscillating fields vary during the optical pulse, which can cause transitions from one state to another. For some special cases not previously known, the transition probabilities and probabilities of no transition are obtained analytically. We give conditions for complete transfer of the atomic population from one state to another, and for complete return to the initial state.

We show that a quantum observable can be measured by coupling it to a meter which in turn interacts with a reservoir. The complete Hamiltonian is chosen so as to allow for an explicit exact solution of the quantum dynamics. In the continuum limit for the bath the solution displays irreversible behavior, two varieties of which, overdamping and amplification, turn out to be of special relevance. We establish the limit in which a suitable pointer variable (i) behaves effectively classically and (ii) acquires, through the measurement, a probability density of its eigenvalues with well-defined peaks each of which corresponds to one discrete eigenvalue of the measured observable. Under a slightly more restrictive condition the reduced density matrix of the object diagonalizes, during the measurement, in the eigenbasis of the measured observable.

The major contribution to forward scattering amplitudes for inelastic electron collisions, from the first Born approximation, is separated out from the remainder in the expressions of differential cross sections and of target orientation, for purposes of analysis. Simple results of this analysis are presented for e+He collisions, as a preliminary to a more detailed analysis of the same data in a separate paper.