We find an anomalously slow trapping rate Q̇ for trapping of nonidentical interacting particles in topologically linear systems with randomly distributed sinks which are selective for particles below a critical radius $r_S$. The particles have an arbitrary size distribution and interact by a hard-core repulsion. Our quantitative result, Q̇∼exp(-${\mathrm{At}}^{1/5}$), is general, and the amplitude A can be tuned since it depends on the concentration of the nontrappable particles.

Excitation rate coefficients for the 1$s_5$, 1$s_4$, 1$s_3$, and 1$s_2$ levels of argon by collisions with low-energy electrons have been measured using a drift-tube technique. Time dependences of the absolute population densities of the excited levels were measured by an absorption method with a tunable diode laser as a light source. The absorption data were analyzed according to the rate equations for these levels and the excitation rate coefficient per unit length of electron drift and per argon-atom density was obtained for each level as a function of the electric field to gas density ratio E/N. The values for the 1$s_5$ level vary from 2.0×${10}^{\mathrm{-}19}$ to 2.5×${10}^{\mathrm{-}17}$ ${\mathrm{cm}}^2$ as E/N increases from 5×${10}^{\mathrm{-}17}$ to 5×${10}^{\mathrm{-}15}$ V ${\mathrm{cm}}^2$. In comparison with these values, those for the 1$s_3$ level are about one-fifth, those for the 1$s_4$ level are about the same, and those for the 1$s_2$ level are slightly larger in respective measured E/N ranges. In order to estimate the cascading effects from the higher-lying levels, excitation rate coefficients for the 2p and 3p levels have also been measured from absolute intensities of the line emissions. From a comparison of all the measured values of the excitation rate coefficients with those calculated from the Boltzmann analysis, a recommended set of cross sections for these levels has been deduced.

Several methods of obtaining properly normalized resonance wave functions and partial widths in multichannel resonance problems are investigated and explicit relationships between these methods are demonstrated. In particular, the normalizations studied include those based on the definition of a resonance state in terms of the poles of the total Green’s function or T matrix, methods based on a study of adjoint resonance states in an adjoint space, normalizations which define formal partial widths which sum precisely to the total width, and the simple branching-ratio method. All methods are applied to a model problem consisting of two open channels and one closed channel.

A new technique has been proposed and outlined to calculate the rearrangement amplitude in the eikonal approximation, taking a consistent account of the internuclear potential term in order to satisfy the boundary condition properly. The six-dimensional integral of the Glauber eikonal transition amplitude has been reduced to a single-dimensional one, which is to be evaluated numerically. Numerical results for the process ${\mathrm{H}}^{+}$+H(1s)→H(1s)+${\mathrm{H}}^{+}$ have been computed for the intermediate- and high-energy regions and have been compared with other existing theoretical results.

The presence of a chaotic laser field with a bandwidth is shown to lead to new resonancelike structures in the double-differential cross sections for electron scattering from a real atomic system, in contrast to potential scattering. On the basis of the exact results, a simpler procedure is suggested to estimate the magnitude of this effect, which explicitly invokes the laser line-shape function and demonstrates how the field correlations affect the projectile and the bound system in markedly different ways. Finally, the feasibility of experimentally detecting these new features is discussed.

For a system of N fermions with Hamiltonian scrH we evaluate matrix elements of the T matrix between arbitrary Slater determinants ‖χ〉,‖χ’〉. The resulting variational equations are driven Hartree-Fock-like equations, with source terms as right-hand sides, due to the ‘‘channels’’ ‖χ〉,‖χ’〉. The validity of this mean-field approximation is illustrated by a numerical example.

Evaluations of parity-violating and charge-parity–violating effects in heavy one-valence-electron atoms, employing the Hartree-Fock potential and several model potentials, are extended to include first-order electron-electron Coulomb corrections using many-body perturbation theory. Parity-conserving quantities, including valence energies, hyperfine splittings, and oscillator strengths, are also calculated and compared with experiment to determine the reliability of the weak-interaction calculations. It is found that the spread between calculations carried out in first-order perturbation theory starting from different potentials is of the same order of magnitude as the spread between the corresponding lowest-order evaluations. It is concluded that second-order many-body perturbation theory must give significant contributions. Some technical problems associated with going to second order are discussed.

We discuss the generation and detection of wave packets of Rydberg states by exciting electrons from a low-lying atomic state with a short pulse to a Rydberg series. To observe the motion of the wave packet, we analyze a time-delayed two-photon experiment, where the first laser pulse generates a wave packet, which is then probed by a second short pulse. The two-photon transition probability shows peaks when the time delay between the pulses is a multiple of the classical orbit time. A semiclassical formalism is developed to describe the motion of the wave packet and to analyze the time-delayed two-photon process.

The collision broadening of Stark-resolved molecular lines is studied both experimentally and theoretically. Accurate measurements are performed on rotational transitions of ${}_{}{}^{12}{}_{}{}^{}\mathrm{CH}_3^{}{}_{}{}^{}$F near 150 GHz and what may be the first experimental evidence of M-dependent pressure broadening of the lines is reported. A simple theoretical model is developed, in the framework of Anderson’s theory, to estimate the broadening coefficients of the Stark-resolved components. The theory predicts that the linewidths may depend on M and their average may be different from the zero-field envelope. The calculated values are in good agreement with experimental results, proving that the theoretical approach described in this work is a useful tool to estimate the relevance of the effect in different cases.

Dielectronic recombination coefficients for ground-state ions of the Ne isoelectronic sequence have been calculated for seven ions, with atomic number 18≤Z≤54, in the isolated resonance approximation, for temperatures in the range 0.2≤T≤6 keV. The Auger and radiative rates of each doubly excited state were evaluated explicitly by using the multiconfiguration Dirac-Fock model. The calculations were performed with intermediate coupling. The effect of the configuration interaction was also included for the low-lying doubly excited states. The effect of Coster-Kronig-type transitions on the dielectronic rate coefficients has been found to be very significant for low-Z ions. However, it is quite small for medium and heavy ions. The effect of relativity on the total dielec- tronic coefficient and dielectronic satellite spectra is also discussed.

Total dielectronic recombination coefficients from F-like to Ne-like selenium have been calculated for three F-like initial states for electron temperatures in the range 0.01≤T≤6 keV/$k_B$. The detailed Auger and radiative rates were evaluated by using the multiconfiguration Dirac-Fock model. Including additional autoionization channels to the excited states of the recombining ion in calculations of the stabilization fluorescence yields leads to a reduction of the total dielectronic coefficients by an amount less than 15%. The peak total dielectronic recombination coefficients are 3.2×${10}^{\mathrm{-}11}$, 4.2×${10}^{\mathrm{-}11}$, and 3.7×${10}^{\mathrm{-}11}$ ${\mathrm{cm}}^3$/sec for the initial ${}_{}{}^2{}_{}{}^{}\mathrm{S}_{1/2}^{}{}_{}{}^{}$, ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{1/2}^{}{}_{}{}^{}$, and ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{3/2}^{}{}_{}{}^{}$ states, respectively.

The energy spectra of electrons generated by collision-free multiphoton ionization of Xe, Kr, Ar, Ne, and He irradiated at intensities up to ∼${10}^{15}$ W/${\mathrm{cm}}^2$ with picosecond 193-nm (6.41-eV) radiation have been studied with an energy resolution of ∼50 meV. The formation of multiply charged ions by a sequential process of ionization has been directly detected in the electron spectra by the observation of a characteristic pattern of interwoven above-threshold-ionization ladder line series. The appearance and relative intensity of specific electron lines depends strongly on the presence of near-resonances and features of the interaction involving the laser pulse shape, saturation, and the shift of the ionization threshold arising from the influence of the ponderomotive potential. The experimental results are compared qualitatively with data from ion time-of-flight experiments and with differing models of multiphoton ionization.

We present ab initio calculations of oscillator-strength sum rules S(μ) and mean exciton energies $I_{\mu }$ for -1≤μ≤1. We use the polarization propagator formalism at the random-phase approximation level. Calculations are performed for ${\mathrm{H}}_2$ and ${\mathrm{H}}_2$O using large basis sets: 90 uncontracted Gaussian-type orbitals (CGTO’s) for ${\mathrm{H}}_2$ and 101 CGTO’s for water. We find that $I_0$=19.12 eV for ${\mathrm{H}}_2$ (including thermal averaging) and 72.46 eV for ${\mathrm{H}}_2$O. They agree very well with previous semiempirical estimates. The same holds for the other $I_{\mu }$ moments. The fulfillment of the Thomas-Reiche-Kuhn sum rule in both the dipole length and velocity formulations shows that the basis sets employed are satisfactory. We have also investigated the ‘‘shell-wise’’ contributions to S(0) and $I_0$ for ${\mathrm{H}}_2$O.

Computations have been made for various ionization processes of atomic hydrogen at 265 nm which correspond to the fourth harmonic of a ${\mathrm{Nd}}^{3+}$-glass laser. Both total and differential cross sections are reported for circular and linear polarization of photons. This is the first reported calculation to our knowledge of the differential cross sections of all processes from four- to ten-photon absorptions which correspond to above-threshold ionization, revealing certain characteristic new features.

The lifetimes of the n ${\mathrm{}}^2$$P_{1/2}$ and n ${\mathrm{}}^2$$P_{3/2}$ states of thallium, n=7–11, have been determined through measurements of the fluorescence signal resulting from two-photon excitation in an atomic beam. The temporal dependence of the fluorescence signal is determined by solving the equations governing cascade spontaneous fluorescence from higher-lying initial states. It is shown that under conditions applicable to our experiments, the asymptotic decay of the fluorescence is a measure of the lifetime of the initial state. The possibility of self-absorption of the fluorescence within the atomic beam is investigated; it is found to be negligible over the range of thallium densities used in the experiment. Our lifetime measurements for these eight ${}_{}{}^2{}_{}{}^{}\mathrm{P}$ states are compared with other known experimental data and with the results of previous semiempirical calculations.

Nonrelativistic Hartree-Fock calculations have been used in intermediate coupling to calculate transition energies and relative intensities for Kα satellites for all elements from K (Z=19) through Ge (Z=32). It is found that the 2s spectator-hole transitions (1s2s${)}^{\mathrm{-}1}$→(2s2p${)}^{\mathrm{-}1}$ contribute negligibly, whereas all satellites except ${\alpha }^{2\mathrm{sprime}}$ can be assigned to allowed transitions from the (1s2p${)}^{\mathrm{-}1}$→(2p${)}^{\mathrm{-}2}$ complex.

The quantum yield of the visible scintillator sodium salicylate is found to increase in the incident photon-energy range 80–270 eV. Because of its use as a photon-flux monitor in recent gas-phase photoelectron spectroscopy measurements, previously reported partial cross sections for Hg (4f, 5p, and 5d subshells) and ${\mathrm{CH}}_3$I (I 4d subshell) in this energy range are corrected, and new values are reported. For Hg, the correction brings the experimental data into better overall agreement with theory. However, considerable uncertainty remains in the absolute scale derived from previous Hg photoabsorption measurements, and no single rescaling of the subshell cross sections could simultaneously bring all three into agreement with available theoretical calculations.

Vibrational levels of the H$1_u$ state in ${\mathrm{Hg}}_2$ excimer molecules, correlated with the 6? sup 1 P sub 1— atomic state, were selectively populated by stepwise excitation using the metastable A$0_g^{\pm }$ states for the intermediate step, and the fluorescence emitted in the H$1_u$→X$0_g^{+}$ bound-free decay was recorded with a spectrometer and a transient digitizer. The uv fluorescence bands, emitted in the decay of several upper-state vibrational levels with v’ ranging from 0 to 5, were centered near 1994 Å and consisted of well-resolved Condon internal diffraction patterns corresponding to appropriate upper-state vibrational wave functions. The energy separation between the A$0_g^{\pm }$ and H$1_u$ potential minima was determined and an estimate was made of the vibrational frequency ${\omega }_e$ of the H$1_u$ state. Much weaker excitation of the H$1_u$ state was also effected from the metastable B$1_g$ state, which allowed the energy separation between the B$1_g$ and A$0_g^{\pm }$ potential minima to be determined experimentally.

Several extensions are made in theoretical studies of multiphoton ionization associated with third-harmonic fields that are generated near three-photon resonances in gaseous media. The treatment includes the strong coherent cancellation effect which occurs between three-photon pumping of a resonant level and pumping by the third-harmonic field that is generated in the same medium. The incomplete spoiling of the cancellation effect with counterpropagating beams is quantitatively described. Also, treatment of the multiphoton-ionization problem involving phase-matched, third-harmonic fields is generalized to include quantitative effects of index changes due to a buffer gas, absorption due to dimers, and collisional dephasing of coherent excitations. Finally, we show how measurements of linewidths, phase-matching positions, and pressure dependences of ionization yields associated with third-harmonic generation and subsequent absorption can be used to determine oscillator strengths of a resonant level, absorption coefficients for a resonant species and a buffer-gas species, and the refractive index of the buffer gas at the third-harmonic frequency.

Unfocused linearly polarized laser beams, in single-pass and counterpropagating configurations, are used in conjunction with absolute ionization measurements in calibrated proportional counters to examine the nature of multiphoton ionization of xenon near three-photon resonances. Mixtures of xenon with other noble gases are also used to incorporate phase matching in order to elucidate additional characteristics of multiphoton ionization in the presence of third-harmonic fields. Point-by-point comparisons are made between theoretically predicted and experimentally observed features of the study. We also show how detailed information on multiphoton ionization involving phase-matched third-harmonic photons can be used to obtain optical constants in the vacuum-ultraviolet region.