Partial photoionization cross sections σ of the 3d and the 4s main lines and the major satellite lines following the photoionization of atomic manganese in the vicinity of the 3p→3d giant resonance are studied in detail using the constant-ionic-state technique. Previously unresolved features are seen revealing the complex structure of this transition-metal atom. Evidence for seven excited states hidden in the giant-resonance region is uncovered. Widths of most of the observed excited states are deduced. The width of the dominant [Ne]3${\mathit{s}}^2$3${\mathit{p}}^5$${\mathit{d}}^6$4${\mathit{s}}^2$${(}^6$P) state is found to be at most 1.5 eV. The origin of a pronounced dip in the partial cross section of the primary 3d photoionization line, which also appears in absorption, is identified. More than 15 resonance features converging to the [Ne]3${\mathit{s}}^2$3${\mathit{p}}^5$3${\mathit{d}}^5$4${\mathit{s}}^2$${(}^7$${\mathit{P}}_{4,3,2}$) limits are observed, and tentative assignments are given. In addition, nonresonant photoelectron spectra recorded from 80 to 120 eV photon energy are examined to determine the behavior of the strongest photoelectron satellite lines and very-high-lying binding energy satellites, which, until now have not been investigated.

We have evaluated the ${\mathrm{\beta }}_{2\mathit{p}}$ and ${\mathrm{\beta }}_2$ asymmetry parameters in the photodetachment of ${\mathrm{H}}^{\mathrm{-}}$ below the N=3 threshold. Results are presented in the regions lying just above the N=2 threshold and just below the N=3 threshold, where the cross sections exhibit resonant structures. We discuss in some detail the role of the ${}_{}{}^1{}_{}{}^{}\mathrm{P}_{}^{\mathit{o}}{}_{}{}^{}$ shape resonance.

Rate coefficients for energy-pooling collisions between low-lying excited states of Ba have been measured. The 6s6p${(}^3$${\mathit{P}}_1$) level in Ba is pumped by a cw diode laser, and radiative decay and collisions with buffer-gas atoms also populate the 5d6s${(}^1$D) and 5d6s${(}^3$D) metastable levels. The densities of these low-lying excited states are measured by the absorption of lines from a Ba hollow-cathode lamp, and the states populated by energy-pooling collisions are studied by comparing their fluorescence intensity to that of the laser-excited level. The rate coefficients are on the order of gas-kinetic rates, and they are not strongly dependent on energy defect, spin changes, or angular-momentum changes.

L-shell ionization cross sections, evaluated as mean values of the experimental data, were compared with the first-order theoretical values obtained by the plane-wave Born and semiclassical method. Hydrogenic Dirac wave functions in the united-atom limit were employed in the calculation. The plane-wave Born approximation cross sections with Dirac-Hartree-Slater wave functions were obtained from the tables of Chen and Crasemann [At. Data Nucl. Data Tables 33, 217 (1985); 41, 257 (1989)]. The agreement between the experimental and semiclassical cross sections was generally better than 20%, except for the ${\mathit{L}}_1$ subshell of heavy elements and for the very adiabatic region of ${\mathit{L}}_{2,3}$ subshells. The differences between both sets of data were largely reproduced by a simplified coupled-channel calculation performed nonrelativistically for a single final state. The calculation also suggests that, due to the uncertainties of the fluorescence yields, the ionization cross sections deduced from the measured data are overestimated by 10%.

With a partial-wave interpolation method we calculated the positron energy spectra of pair production in the field of uranium atoms for photons of energy k=10 MeV, permitting a comparison of theory with the recent experiment. Our results show that the atomic-electron screening effect decreases the cross section for the main region of the positron energy spectra which contributes to the total pair-production cross section, and the effect can be as large as about 9% for the region of low positron energies which contributes little to the total pair-production cross section. The screening effect to the total pair-production cross section is about 3.5%. Our results also indicate that the approximate treatment of screening through energy-shift screening theory becomes inadequate at this intermediate photon energy, while the approximate treatment of screening through form-factor screening theory is quite good. Our result for the total pair-production cross section is compared with the experimental result.

The limits of validity of the nonrelativistic dipole formulation of the total photoionization cross section are explored. Relativistic and nonrelativistic independent particle model calculations of all subshells of C, Sn, and U are performed from 0 to 200 keV above threshold in each case. The comparison shows a remarkable agreement between nonrelativistic dipole and full relativistic multipole results for s subshells, even at the highest energies investigated where nonrelativistic dipole approximation should show significant breakdown; this phenomenon does not occur for l≠0 subshells or in angular distributions. The phenomenon is explained in terms of an approximate cancellation among relativistic, retardation, and multipole effects which occurs only for s subshells.

The hyperspherical close-coupling method is used to compare the detailed structures in the photoionization spectra of He(1 ${}_{}{}^1{}_{}{}^{}$ S) and ${\mathrm{He}}^{\mathrm{*}}$(2 ${}_{}{}^1{}_{}{}^{}$S) between the ${\mathrm{He}}^{+}$(n=4) and ${\mathrm{He}}^{+}$(n=6) thresholds; both the total photoionization cross section and the partial cross sections for the production of ${\mathrm{He}}^{+}$(n) are studied. Some doubly excited resonance series of excited angular modes that are either weak or unobservable in the ground-state spectrum are greatly enhanced in the metastable-state spectrum. This corroborates that previously derived propensity rules do not apply, in fact, to the photoionization of ${\mathrm{He}}^{\mathrm{*}}$(2 ${}_{}{}^1{}_{}{}^{}$S). The dependence of the propensity rules on the initial state is interpreted in terms of the correlation patterns of its wave function in the region of the hyperradius that contributes dominantly to the photoionization cross section. This interpretation suggests a generality of the enhancement of some resonance series in excited-state spectra. Some overlapping resonances that are overlooked in the literature are uncovered and analyzed by using the Gailitis-average procedure.

The angular distribution, as well as the energy distribution of δ electrons produced in collisions of 1.0-MeV/u ${\mathrm{F}}^{\mathit{q}+}$ (q=4,6,8,9) ions with molecular hydrogen, have been studied for laboratory observation angles (${\mathrm{\theta }}_{\mathit{L}}$) from 0° to 70° with respect to the beam direction. The measurements are in fair agreement with the impulse approximation calculations which use the quantal elastic electron-ion differential scattering cross sections folded with the Compton profile of the target electrons. We observe that the energy of the centroid of the binary-encounter-electron (BEE) peak is projectile charge state, q, and laboratory angle, ${\mathrm{\theta }}_{\mathit{L}}$, dependent. Moreover, at 0°, an enhancement of the ratio of the observed double differential cross section for nonbare projectiles to that for the bare ion projectiles, σ(q+)/σ(9+), is observed, contrary to the ${\mathit{q}}^2$ scaling predicted by a first Born calculation for ionization. This ratio σ(q+)/σ(9+) decreases nonotonically with increasing ${\mathrm{\theta }}_{\mathit{L}}$, and becomes smaller than one for ${\mathrm{\theta }}_{\mathit{L}}$≥30°.

Autoionization probabilities of doubly excited atoms with one electron in a large-l Rydberg state are investigated through first-order perturbation theory in a single-configuration approach. In the framework of the jk-coupling scheme, the formalism takes into account multipoles higher than dipoles in the electronic interaction and exchange effects. Exchange effects are computed using the Froese method for Slater integrals and are demonstrated to be significant as long as l<5. The essential importance of fine-structure transitions when the outer electron is in a large-l state is emphasized. Comparison with available experimental data shows that Slater integrals are reliably computed and that fair agreement is generally obtained for g states, while even strongly autoionizing f states are at least qualitatively represented. Correlation effects may explain some remaining disagreement with the measured autoionization widths.

A time-dependent approach to the study of atomic autoionization in two-electron systems is formulated. In the first step a two-dimensional (2D) model ‘‘He’’ atom is constructed by replacing the full 3D electrostatic interaction with a 1D soft-core interaction. The autoionization decay of doubly excited states constructed within the model is calculated by both standard perturbation theory and direct solution of the time-dependent Schrödinger equation. Configuration-interaction theory is invoked to obtain correlated resonance states, and strong laser fields are found to alter the decay rates. In the second step the full 6D wave function for the He atom is expanded in coupled spherical harmonics using a procedure as described by C. Bottcher, D. R. Schultz, and D. H. Madison [Phys. Rev. A 49, 1714 (1994)]. Solution of the time-dependent Schrödinger equation reduces to solving the propagator equations for the 3D expansion coefficients on a B-spline collocation lattice. Autoionizing decay rate calculations using product resonance states are found to be in qualitative agreement with the 2D model results.

The evolution of K-${\mathit{L}}_{2,3}$${\mathit{L}}_{2,3}$ ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$ radiationless resonant Raman scattering into Auger-electron emission was studied by tuning synchrotron radiation across the K edge of P in InP. The spectrum can be interpreted in terms of a two-component model that involves excitation of a photoelectron (1) into a discrete excitonlike state and (2) into the continuum; extra-atomic relaxation is taken into account. Auxiliary studies of above-threshold Auger and photoelectron spectra arising from K photoionization were used to identify the dominantly atomic features of these spectra.

The self-consistent-field model for K shakeoff in ${\mathrm{\beta }}^{\pm }$ decay and electron-capture decay is extended to deal with the processes of L shakeoff accompanying K capture and K shakeoff accompanying L capture. The results indicate that many-body effects play an important role and reduce the shakeoff probability.

Experimental measurements of absolute cross sections are presented for electron-impact single ionization of ${\mathrm{Si}}^{4+}$ and ${\mathrm{Si}}^{5+}$. The incident electron energies range from below threshold to 1500 eV. The measurements were performed using the crossed ion-electron beams apparatus at the Oak Ridge National Laboratory Electron-Cyclotron Resonance Ion-Source Facility. The data are in reasonable agreement with cross sections calculated using the Lotz semiempirical formula. Reduced cross sections for the isoelectronic targets, ${\mathrm{Si}}^{4+}$ and ${\mathrm{Ar}}^{8+}$, are compared in order to test classical scaling for direct electron-impact single ionization.

The results of close-coupling calculations using the complex Kohn variational method are reported for a variety of low-energy electron-collision processes involving molecular chlorine. We report cross sections for elastic scattering and momentum transfer, as well as dissociative excitation of the five lowest electronically excited states ${(}^{1,3}$${\mathrm{\Pi }}_{\mathit{u}}$, ${}_{}{}^{1,3}{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$, ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$) which are formed by promoting an occupied valence electron into an antibonding (5${\mathrm{\sigma }}_{\mathit{u}}$) orbital. We also report cross sections for the excitation of the lowest bound optically allowed states in ${\mathrm{Cl}}_2$. The cross sections, especially at very low energies, are found to depend sensitively on both target polarization and a proper balance of correlation effects in the N- and (N+1)-electron systems. Comparison is made between the results of this study and the limited body of experimental results available for this system.

We investigate analytically multipole and retardation effects on Rayleigh scattering of photons from the ground state of a hydrogenic atom. Our approach, which goes beyond the usual form-factor approximation, simplifies the full nonrelativistic point-Coulombic amplitude considerably. We are able to express this simplified full multipole, fully retarded result as simple corrections to the nonrelativistic dipole amplitude. We demonstrate that these corrections are important, and larger than relativistic effects, for photon energies near the K-shell photoionization threshold. They are essential for accurately determining the angular distribution of scattered photons in this regime. We present numerical comparisons with relativistic S-matrix calculations that confirm the validity of our approach in this region for elements of low to moderate nuclear charge. For photon energies well above the K-shell threshold we show that retardation corrections are adequately given by the form factor, which has a greater variation with angles than the anomalous scattering factors. For still higher energies, we demonstrate that the full nonrelativistic result fails due to spurious poles in the imaginary part of the amplitude.

The absolute photodissociation cross section of the 1 ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$←1 ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$ transition in ${\mathrm{Na}}_2^{+}$ over the wavelength range from 480 to 655 nm has been measured using nanosecond pulsed lasers, a molecular beam, and a time-of-flight mass spectrometric detection scheme. We present a detailed discussion of the procedure to extract absolute values of the cross section from the experimental data. The cross section has a maximum of (9±1)×${10}^{\mathrm{-}17}$ ${\mathrm{cm}}^2$ at about 540 nm. Our results agree satisfactorily with previous experimental measurements at 492.2 and 604.0 nm, and also agree in absolute size within a factor of about 2 with theoretical predictions.

Our aim in this paper is to study classical dynamics in two-level molecular systems. We first derive, through the Wigner phase-space transform, a classical limit that reduces unfortunately to the adiabatic approximation. This lead us to develop a one-center quantal approximation whose variables can be interpreted in a fully classical Hamiltonian scheme. As a prominent feature, this Hamiltonian couples polarization and spatial motion. We apply it successfully to the Rosenthal-Stückelberg oscillations. We analyze one-dimensional diffusion similar to a molecular reaction, it appears to exhibit chaotic behavior.

In the present paper we study the effects in the rainbow differential cross sections of using higher-order phase-integral residues in the pole sum of the scattering amplitude. We have recently found that already in the first-order approximation the uniform residue formula, derived by Fröman and Fröman, provides an important means for an accurate calculation of the rainbow differential cross section where reliable numerical quantum methods are not available. From the present investigation it is clear that the use of higher-order approximations is not the crucial step to further reveal the rainbow structures in the cross section. For that purpose, it is instead essential to increase the purely numerical precision (in any order) of the uniform phase-integral residue calculations.

Secondary electron spectra of the H-like ${\mathrm{Ne}}^{9+}$ ion incident with impact energies of 135 eV up to 90 keV on a solid Al(111) surface were measured. The dependence of the K Auger electron yield on the angle of observation is studied in detail. It is found to be cosine like in case of the 90-keV ${\mathrm{Ne}}^{9+}$ ions and to be more and more isotropic at lower ion energies although a clear anisotropy remains. Information about the rates of the filling of the L and K shells inside the solid is obtained from a comparison of the measured angular distributions with the calculation of a two-step model for the successive filling of the L and K shells. The data show clear evidence for Auger electron emission from below the surface for ion energies as low as 135 eV.

The penetration of 576-keV ${\mathrm{Ar}}^{\mathit{q}+}$ ions with initial charge states ${\mathit{q}}_{\mathit{i}}$=8,12,16 through a carbon foil of 310 Å thickness has been investigated. The projectile’s energy loss and final charge-state distribution have been measured. Within a resolution of a few percent no dependence of these data on the projectile’s initial charge state was found. Furthermore the relative yield of Auger electrons emitted by the projectile before and after the foil was detected. From these yields we could derive that the Ar ions quickly reach an equilibrium excitation state inside the foil that does not depend on the initial charge state ${\mathit{q}}_{\mathit{i}}$. From the measured energy-loss data we derive an upper limit for the projectile’s average charge-state equilibration length ${\mathit{x}}_{\mathit{e}}$ inside the foil of approximately one carbon layer. This result implies extremely large cross sections for electron transfer mechanisms between projectile and solid. An estimation of this cross section by using the classical over-barrier model hardly explains the observed, very large charge-exchange cross sections between ion and solid.