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The cross sections for single-electron capture, including transfer ionization, and for double-electron capture, have been measured for Ar{sup {ital q}+}+H{sub 2} for {ital q}=6, 7, 8, 9, and 11 with projectile energies from {ital q} eV to {ital q} keV. Theoretically, the cross sections for Ar{sup 6+} and Ar{sup 8+} impact were calculated using a molecular-orbital expansion method in the energy region from 240 eV to 80 keV, and are in good agreement with experiment. The single-electron-capture cross sections were found to be more than one order of magnitude larger than those for double capture in both experiment and theory. The single-electron-capture cross sections were also compared to the Langevin cross section, a scaling law developed by Mueller and Salzborn [Phys. Lett. 62A, 391 (1977)], and the absorbing sphere model.

Projectile {ital K}{alpha} satellite and hypersatellite x-ray yields were measured in collisions of Ar ions with energies of 43, 52, 65, 80, 95, and 300 MeV with targets of C, Mg, Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, Sn, Nd, Tb, Ho, Ta, and W with atomic number {ital Z}{sub {ital t}}=6--74. The intensity ratio of hypersatellite to satellite lines is reported as functions of the target atomic number {ital Z}{sub {ital t}} and incident energy {ital E}{sub {ital p}}. The vacancy-sharing model was found to predict the {ital Z}{sub {ital t}} dependence of the intensity ratio at 43 MeV in near symmetric collisions. At energies above 80 MeV, the direct Coulomb processes, exspecially the electron-capture processes, determine the {ital Z}{sub {ital t}} dependence. Average {ital L}-vacancy probabilities are reported for projectiles at energies of 43--95 MeV that acquire single and double {ital K} vacancies in the targets.

Rydberg-valence (RV) mixing and doublet-quartet (DQ) interchannel coupling in the core-excited states of triplet open-shell O2 are experimentally and theoretically unveiled through the resonant ine ...

Vibrationally resolved O 1s photoelectron angular distributions from CO{sub 2} molecules, aligned parallel and perpendicular to the electric vector of the incident light, have been measured in the 5{sigma}{sub g}* shape resonance region, with photon energies up to 2 eV above the O 1s ionization threshold, using multiple-coincidence electron-ion momentum imaging spectroscopy. The angular distributions depend on the vibrational quanta of the antisymmetric vibrations in the O 1s ionized state but do not vary significantly as a function of the photon energy across the 5{sigma}{sub g}* shape resonance.

We have applied a high-resolution-electron-momentum-resolved-ion coincidence technique to the Auger emission from CF{sub 4} following the F 1s{yields}a{sub 1}* excitation and found that the Auger electron emitted from the atomic F fragment during the ultrafast dissociation is backscattered by the residual fragment CF{sub 3}. We find also that more than half of the excess energy goes into the vibrational excitation of the CF{sub 3} fragment.

The photoabsorption spectrum of Ne in the excitation energy region of the $[1s2s](^{3,1}S)n\mathcal{l}{n}^{\ensuremath{'}}{\mathcal{l}}^{\ensuremath{'}}$ doubly excited states has been measured using high brilliant soft x-ray undulator radiation, where square brackets indicate hole states. The observed absorption spectrum was analyzed with the aid of theoretical calculations based on the multiconfiguration Dirac-Fock (MCDF) method. The computation has revealed that the observed features are successfully assigned with several series of the resonant double excitations, such as the $[1s2s](^{3,1}S)3snp$ $(3\ensuremath{\leqslant}n\ensuremath{\leqslant}6)$ and the $[1s2s](^{3}S)3pns$ $(4\ensuremath{\leqslant}n\ensuremath{\leqslant}6)$ series. The $[1s2s]n\mathcal{l}{n}^{\ensuremath{'}}{\mathcal{l}}^{\ensuremath{'}}$ double excitation resonance leading to the lowest $[1s2s](^{3}S)3s3p$ state was analyzed using the well-known parametrized Fano profile. The energy as well as the width of the resonance for such highly correlated multiply excited state have been determined and the possible decay channels for the $[1s2s](^{3}S)3s3p$ state were also discussed.

We use recapture of near-threshold photoelectrons by postcollision interaction with Auger electrons as an effective method for population of the high-Rydberg states of subvalence ionized Ne ions. The subsequent intermultiplet Auger transitions are detected by high-resolution electron spectrometry. The series of transitions $2{p}^{4}(^{1}D)np\phantom{\rule{0.3em}{0ex}}^{2}D,^{2}F\ensuremath{\rightarrow}2{p}^{4}\phantom{\rule{0.3em}{0ex}}^{3}P$ up to $n=20$ are observed and identified with the help of multiconfiguration Dirac--Fock ab initio calculations.

A high-resolution photoabsorption spectrum of $\mathrm{Ne}$ has been measured in the energy range of the $[1s2p]n\ensuremath{\ell}{n}^{\ensuremath{'}}{\ensuremath{\ell}}^{\ensuremath{'}}$ doubly excited states, where square brackets indicate hole states, by means of photoion yield spectroscopy. The observed features have been interpreted by adopting a simple Rydberg formula. Energies as well as quantum defects for the members of the $[1s2p](^{3,1}P)3pnp$ $(3\ensuremath{\leqslant}n\ensuremath{\leqslant}5)$ series have been determined. We report observations of angle-resolved spectra of the resonant Auger (RA) transitions to the ${\mathrm{Ne}}^{+}$ $[2{p}^{3}]3{p}^{2}$ states and to the ${\mathrm{Ne}}^{+}$ $[2s2{p}^{2}]3{p}^{2}$ states from the $[1s2p](^{3,1}P)3{p}^{2}$ doubly excited states. These double-spectator-type transitions are confirmed by a good general agreement between the measured and theoretical RA spectra, where theoretical spectra are calculated based on the Hartree-Fock approximation. The measured anisotropy parameters are compared with theoretical predictions calculated using a pure $LS$ coupling approach. We have made assignments for several levels with the aid of theoretical calculations.

Angular distribution of L x rays of Au and Pb following photoionization by synchrotron radiation has been measured at the incident photon energies corresponding to the energy between ${L}_{3}$ and ${L}_{2},$ between ${L}_{2}$ and ${L}_{1},$ and above ${L}_{1}$ absorption edges. No evidence of L x-ray anisotropy was observed within the experimental errors for all incident photon energies, but in the case of ${L}_{l}$ x rays an anisotropy of a few percent might be possible. The experimental results are in good agreement with the theoretical prediction.

Photoion yields from ${\mathrm{Ne}}^{+}$ to ${\mathrm{Ne}}^{2+}$ and from ${\mathrm{Ne}}^{2+}$ to ${\mathrm{Ne}}^{3+}$ were measured near the K-shell $(1s\ensuremath{-}2p)$ autoionizing resonance region in the 841--858-eV and 850--863-eV photon energy range, respectively. Measurements were performed using a photon-ion merged-beam apparatus with an electron cyclotron resonance ion source. Multiconfiguration Dirac-Fock calculations were performed to interpret the experimental results. The calculations show fairly good agreement with the experimental results. Isonuclear series for the photoionization of ${\mathrm{Ne}}^{+},$ ${\mathrm{Ne}}^{2+},$ and ${\mathrm{Ne}}^{3+}$ are discussed.