The R-matrix method for electron-molecule collisions has been applied to autoionizing doubly excited adiabatic states of ${\mathrm{H}}_2$ with ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$ symmetry for internuclear distances from 1 to 5 a.u. Above the previously known three states we have found many other doubly excited states for the first time. These states are classified into two Rydberg series, namely, (1${\mathrm{\sigma }}_{\mathit{u}}$)(npσ) and (1${\mathrm{\sigma }}_{\mathit{u}}$)(nfσ) series up to n=10. They are characterized by their complex quantum defect, the imaginary part corresponding to the width of each Rydberg state. For the smaller internuclear distances R these Rydberg states are isolated resonances, but for R>4 a.u. some of them begin to overlap and present a problem of multichannel autoionizing Rydberg series, although there is only one common series limit in the present case. This work exemplifies the usefulness of the R-matrix method for studying molecular doubly excited Rydberg states.

We have calculated differential cross sections for the process of resonant transfer excitation followed by Auger emission (RTEA) in collisions of H-like fluorine with ${\mathrm{H}}_2$. At energies below the KL∞ limit, our results for the emission of KLL, KLM, and KLN Auger electrons agree qualitatively with the experimental results of Schulz et al. [Phys. Rev. Lett. 62, 1738 (1989)] for transfer excitation (TE) that have been normalized to our KLL RTEA cross section at 48 Ry. Together with our RTEA results for KLO emission, this implies that RTE is the dominant TE mechanism at these energies for all n values measured so far although uncorrelated transfer excitation may be important at high energies. The absolute cross sections of Schulz et al. are about a factor of 12 smaller than theory.

Electron capture and ionization processes were investigated for ${\mathrm{I}}^{\mathit{q}+}$-He and ${\mathrm{U}}^{\mathit{q}+}$-He collisions at incident energies 0.1–1.0 MeV/nucleon and for incident charge states q=5–44. Cross sections for single-electron capture, transfer ionization, single ionization, and double ionization were obtained using a projectile-ion recoil-ion coincidence technique. A pronounced interplay among the different electronic processes was observed. Cross sections for single ionization show a rather weak charge-state dependence, in disagreement with recent calculations of McKenzie and Olson [Phys. Rev. A 35, 2863 (1987)]. In a second experiment, photon recoil-ion coincidences were measured to obtain partial cross sections for capture into certain projectile n states. These measurements provide strong evidence that transfer ionization populates lower projectile n states than does single-electron capture. Zero-degree electron spectroscopy, coincident with charge capture for 0.5 MeV/nucleon ${\mathrm{U}}^{30+}$ projectiles revealed that the free electron in transfer ionization is released from the projectile to its continuum and from high-lying Rydberg states of the projectile.

The photoion yield spectra of singly and doubly charged lanthanides Gd, Tb, Dy, Ho, Er, Tm, and Yb were measured in the region of the 5p excitation between 20 and 40 eV. Monochromatized synchrotron radiation was focused on an atomic beam and a time-of-flight spectrometer was used for the charge-selective detection of the photoions. The interpretation of the experimental results is partly based on time-dependent local-density approximation calculations of the partial photoionization cross section of the subshells 4f, 5p, 5d, and 6s.

Absolute electron-impact cross sections have been measured from 0 to 200 eV for single ionization of 16 atoms (Mg, Fe, Cu, Ag, Al, Si, Ge, Sn, Pb, P, As, Sb, Bi, S, Se, and Te) with an estimated accuracy of ±10%. Combined with our recent measurements of He, Ne, Ar, Kr, Xe, F, Cl, Br, I, Ga, and In [Wetzel et al., Phys. Rev. A 35, 559 (1987); Hayes et al., ibid. 35, 578 (1987); Shul, Wetzel, and Freund, ibid. 39, 5588 (1989)], a set of 27 atomic single-ionization cross sections has now been measured with the same apparatus. In addition, cross sections are reported for double ionization of ten atoms and triple ionization of eight atoms. The measurements are made by crossing an electron beam with a 3-keV beam of neutral atoms, prepared by charge-transfer neutralization of a mass-selected ion beam. The critical measurement of absolute neutral beam flux is made with a calibrated pyroelectric crystal. The magnitudes of the single-ionization-peak cross sections decrease monotonically across rows of the periodic table from group IIIA (Al,Ga,In) to group VIIIA (Ar,Kr,Xe), varying much more than predicted by various empirical formulas and classical and quantum-mechanical theories.

It is theoretically pointed out that, even between strongly correlated doubly excited states, there exist single-electron–type transitions for electron-impact excitation processes of He atoms in doubly excited states under the condition ΔL=0, where L is the total orbital angular momentum of the atom. The propensity rules found for the ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$${\mathrm{-}}^1$${\mathit{P}}^{\mathit{o}}$ and ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}^{\mathit{e}}$${\mathrm{-}}^1$${\mathit{D}}^{\mathit{e}}$ double-excitation processes are also presented and discussed based on the rovibrational interpretation of the collective motion of two atomic electrons.

Electron-impact-ionization cross sections are calculated for hydrogenic ions with nuclear charge between 26 and 92, for incident electron energies up to 8 times the ionization energy, by a relativistic distorted-wave method. The results demonstrate the increasing importance of relativistic effects with Z and with incident electron energy, particularly for 1s ionization. The effects of including magnetic and retardation interactions as Z increases are also studied. Results are compared with scaled K-shell ionization measurements for ${}_{}{}^{47}{}_{}{}^{}\mathrm{Ag}$ and ${}_{}{}^{79}{}_{}{}^{}\mathrm{Au}$.

We have investigated the role played by initial rovibrational excitation of ${\mathrm{Li}}_2$ on the cross sections and rates for dissociative electron attachment to the molecule. For a given internal energy, the vibrational excitation enhances the attachment cross section more than the rotational excitation. The attachment cross sections and the attachment rates reach their maximum values when the process of dissociative attachment to rovibrationally excited molecules is still endoergic and, furthermore, these quantities stay close to their maximum values even when the process changes from being endoergic to exoergic. The upper bounds on the cross sections and the rates for dissociative electron attachment to ${\mathrm{Li}}_2$ are 12.8 A${\mathrm{̊}}^2$ and 1.25×${10}^{\mathrm{-}8}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$. At a fixed electron temperature, the kinetic energy of the negative ion formed by this process increases as the vibrational quantum number of the initial neutral molecule increases; the maximum kinetic energy of the ${\mathrm{Li}}^{\mathrm{-}}$ ion formed by attachment to the v=12 level of ${\mathrm{Li}}_2$ is 0.153 eV.

The photoionization cross sections of the 4${\mathit{d}}^{10}$, 5${\mathit{s}}^2$, 5${\mathit{p}}^6$, and 6${\mathit{s}}^2$ subshells of atomic barium and the angular distribution asymmetry parameters for the 4${\mathit{d}}^{10}$ and 5${\mathit{p}}^6$ subshells have been calculated using many-body perturbation theory. Our main purpose is to determine whether relaxation and polarization effects can account for the large difference between recent 4d photoemission experiments and total absorption experiments. Coupling between a number of LS-coupled final-state channels has been included. Relaxation effects have been included by evaluating many-body diagrams and also by calculating excited orbitals in the field of the relaxed ionic core. In the latter case, overlap integrals between initial- and final-state orbitals of the spectator electrons were included. Polarization effects have been included by evaluating many-body diagrams. Results are compared with experiments and other calculations.

The total cross section and the single-differential cross section in energy for the ionization of the ground-state helium atom by electron impact have been calculated in distorted-wave approximations. The optical potential, or self-energy of the single-particle Green’s function, was used to investigate effects of electron correlations in the initial state. Our results are compared with the results of experiments and other calculations.

A three-dimensional model is studied in which a particle moves in the field of two colliding zero-range potentials. Exact wave functions are constructed for the case of a head-on collision. The probability distribution of the ejected particle in momentum space is investigated. The numerical calculations are compared with the results of the adiabatic approximation.

Experimental and theoretical values of the Barkas function ${\mathit{L}}_1$ are compared for p, p¯, α, and Li ions. For a gold absorber, existing theories of ${\mathit{L}}_1$ do not provide a good approximation for the experimental data. Therefore an empirical function is suggested. For Al, Si, Cu, and Ag, parameters b and χ for the Ashley, Ritchie, and Brandt theory [Phys. Rev. B 5, 2393 (1972)] have been determined that give fairly good agreement with experiment for particle energies above 1 MeV/u. The Bloch term ${\mathit{L}}_2$ is used without any modifications. For Li ions, the charge-state corrections ${\mathit{z}}^{\mathrm{*}}$ used so far appear to be too large. In order to derive reliable experimental values of ${\mathit{L}}_1$ from p- and α-particle data, measurements of stopping power should have an uncertainty of the order of 0.1%.

Microwave spectroscopy of high-L (0,1)${\mathit{nL}}_{\mathit{N}}$ Rydberg states of ${\mathrm{H}}_2$, with 26≤n≤30 is reported. The results show a strong perturbation at n=28 due to the nearly degenerate (0,3)16${\mathit{L}}_{\mathit{N}}$ states. Mixing between members of these two Rydberg series results in energy perturbations that can be measured quite precisely (≤1%) from the microwave spectra and that are found to be in good agreement with a priori predictions based on the interseries matrix elements of the polarization potential. The connection between this use of the polarization potential and the systematic derivation of the polarization model from perturbation theory is discussed.

The frequencies of the four strongest magnetic-fine-structure components of the 10F–10G and 10G–10H transitions in atomic helium have been measured to within a precision of a few kHz. The measurements are made with fast-beam microwave-optical techniques similar to previous measurements. Two significant experimental improvements are (1) the use of a new scheme to select a single magnetic-fine-structure component for careful study, and (2) improved control over systematic errors due to stray electric fields. The measured intervals can be combined with other measurements and with precise calculations of high-L states to yield absolute binding energies of the 10F and 10G states of helium with a precision of about 4 kHz (2×${10}^{\mathrm{-}13}$ a.u.). These energies are compared to calculations of the structure, and when combined with expected calculations, will give a high-precision test of the calculated structure of these states, including a 1% test of retardation effects.

In a recent perturbative treatment of the effects of magnetic-field inhomogeneities on nuclear spin relaxation of gases, the lowest-order contributions to the relaxation rate were predicted to be proportional to the square of the field inhomogeneity. However, recent experiments show that under magnetic-resonance conditions the observed relaxation rates can have comparable contributions from both the square and the fourth power of the field inhomogeneity. For a fixed magnetic-field inhomogeneity, the quartic contribution will always dominate at sufficiently high pressures. There are no noticeable contributions proportional to higher powers of the field inhomogeneity under the experimental conditions we have explored. In this paper we extend the perturbative theory of spin relaxation in inhomogeneous magnetic fields to account for these quartic effects. We present measurements in which spin relaxation in inhomogeneous magnetic fields is used to determine the diffusion constant of Xe in 760 Torr of either He or ${\mathrm{N}}_2$ at 80 °C to be 0.791±0.032 and 0.21±0.03 ${\mathrm{cm}}^2$/sec, respectively. Using our measured diffusion constants, we show that our theory describes well the observed quartic effects.

Very extensive multiconfiguration Dirac-Fock calculations done through the alternative special average-level version [Polasik, Phys. Rev. A 40, 4361 (1989)] with the inclusion of the transverse (Breit) interaction, self-energy, and vacuum polarization corrections have been performed on palladium to shed light on the structure of the Kα${\mathit{L}}^1$${\mathit{M}}^{\mathit{r}}$ satellite lines in its x-ray spectra and moreover, to explain the influence of additional holes in the M shell on the shapes and positions of Kα${\mathit{L}}^1$ satellite bands. For each type of Kα${\mathit{L}}^1$${\mathit{M}}^{\mathit{r}}$ line two theoretical spectra have been synthesized: one a sum of the Lorentzian natural line shapes and the other a convolution of the sum of the Lorentzian natural line shapes with a Gaussian instrumental response. It has been found that in some cases the structures of Kα${\mathit{L}}^1$${\mathit{M}}^{\mathit{r}}$ satellite lines are extremely complex and the distances between the neighboring lines are very small. It has been also observed that the effect of M-shell holes smooths the shapes of the Kα${\mathit{L}}^1$ satellite bands. Moreover, the positions of the resultant bands are shifted and their shapes more closely resemble the Voigt profiles than the reference Kα${\mathit{L}}^1$${\mathit{M}}^0$ bands. It has been concluded that removing a 3p electron is more effective in producing a Kα${\mathit{L}}^1$ energy shift than removing a 3s or 3d electron. The results of this and previous papers of this series can be used for theoretical simulations of various experimental Kα${\mathit{L}}^{\mathit{n}}$ spectra of palladium generated by different inducing projectiles.

We report results of a high-resolution inverse Raman spectroscopy study of the dependence on temperature and rotational quantum number J of the Raman Q-branch self-density-shift coefficients of pure (natural) hydrogen. The population-correlated J dependence of these coefficients, previously established at lower temperatures as a ‘‘coupling shift,’’ is observed to persist, almost independent of temperature, up to 1000 K. The temperature dependence of the overall shift is found to disagree above 500 K with extrapolations of recent theoretical calculations.

Resonant Raman-Compton scattering has been studied with synchrotron radiation in the vicinity of the K absorption edge of zirconium. The full spectrum, including the infrared divergence has been studied in a wide energy range on targets of various thicknesses. Absolute cross sections have been measured and compared to theoretical calculations.

S LVV and F KVV resonance Auger spectra have been studied from ${\mathrm{SF}}_6$ gas-phase molecules using selective excitation of S 2p and F 1s electrons to different resonance states with high-resolution monochromated synchrotron radiation for S 2p and with lower resolution for F 1s. The normal Auger spectra were measured using both synchrotron radiation and high-energy electron-beam excitation. The kinetic energy shift of the resonance S LVV and F KVV Auger spectra (with a spectator electron in the 6${\mathit{a}}_{1\mathit{g}}$ orbital) relative to the normal Auger spectra are 11.0 and 8.0 eV, respectively. These values, in comparison to the 7.5 eV for the Si LVV Auger shift in ${\mathrm{SiF}}_4$, are discussed. The spectator Auger process is the dominating decay channel, but, in the case of S, the participating or autoionization decay channel is also found to be important in enhancing the intensity of bonding levels such as the 4${\mathit{t}}_{1\mathit{u}}$ level in the outer valence band and especially the 4${\mathit{a}}_{1\mathit{g}}$ and 3${\mathit{t}}_{1\mathit{u}}$ inner valence-band levels with significant sulfur character. No significant changes in Auger or valence-band spectra were seen at intense above-edge resonances, such as the ${\mathit{e}}_{\mathit{g}}$ resonance at 196-eV photon energy.

The Liapunov exponents of the classical hydrogen atom in a uniform magnetic field allow a comparison with the chaotic quasi-Landau spectrum for transitions of the type ${\mathit{m}}_{\mathit{i}\mathit{f}}$=0. Characteristic frequencies were also obtained.