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Double and triple detachment of the ${\mathrm{F}}^{\ensuremath{-}}(1{s}^{2}2{s}^{2}2{p}^{6})$ negative ion by a single photon have been investigated in the photon energy range 660 to 1000 eV. The experimental data provide unambiguous evidence for the dominant role of direct photodouble detachment with a subsequent single-Auger process in the reaction channel leading to ${\mathrm{F}}^{2+}$ product ions. Absolute cross sections were determined for the direct removal of a $(1s+2p)$ pair of electrons from ${\mathrm{F}}^{\ensuremath{-}}$ by the absorption of a single photon.

Single, double, and triple ionization of C(1+) ions by single photons is investigated in the energy range of 286-326 eV, i.e., in the range from the lowest-energy K-vacancy resonances to well beyond the K-shell ionization threshold. Clear signatures of C(1+)(1s2s(2)2p(2) (2)D,(2)P) resonances are found in the triple-ionization channel. The only possible mechanism producing C(4+)(1s(2)) via these resonances is direct triple-Auger decay, i.e., a four-electron process with simultaneous emission of three electrons.

Radiative recombination (inverse photoionization) is believed to be well understood since the beginning of quantum mechanics. Still, modern experiments consistently reveal excess recombination rates at very low electron-ion center-of-mass energies. In a detailed study on recombination of F and C ions with magnetically guided electrons we explored the yet unexplained rate enhancement, its dependence on the magnetic field B, the electron density n(e), and the beam temperatures T-perpendicular to and T-parallel to. The excess scales as T-perpendicular to(-1/2) and, surprisingly, as T-parallel to(-1/2), increases strongly with B, and is insensitive to n(e). This puts strong constraints on explanations of the enhancement.

We have obtained experimental photo-double- and photo-triple-detachment cross sections for the fullerene negative ion using Advanced Light Source photons of 17-90 eV. The cross sections are 2 and 2.5 times larger than those for C60 and appear to be compressed and shifted in photon energy as compared to C60. Our analysis reveals that the additional electron in C60- primarily produces screening which is responsible for the modification of the spectrum. Both screening effects, the shift and the compression, can be quantitatively accounted for by a linear transformation of the energy axis. Applying the transformation allows us to map the neutral and negative ion cross sections onto each other, pointing out the close relationship of correlated few-electron dynamics in neutral and negatively charged extended systems. In contrast, dynamics of neutral and negatively charged atoms or small molecules are typically not closely related.

We report on measurements of scattered projectile angular and charge state distributions for 3.75 keV/amu O{sup {ital q}+} (3{le}{ital q}{le}8) ions surface channeled along the {l_angle}1{bar 1}0{r_angle} direction of a Au(110) single crystal target. Projectile trajectory calculations indicate that the projectiles spend less than 30 fs within 2 A of the topmost Au surface layer. Nevertheless, almost complete charge equilibration is observed in the scattered projectile charge state distributions. It is concluded that, {ital already} {ital at} {ital the} {ital target} {ital interface}, strong screening effects are present which make possible direct capture to the projectile {ital L} and {ital M} shells in relatively large impact parameter collisions.

We present high resolution KLL Auger spectra emerging from collisions of H-like and metastable He-like C, N, and O on a B-doped Si(100) surface. In combination with the high resolution electron spectroscopy, Hartree-Fock calculations allow us to succesfully identify KLL Auger electrons arising from specific states that form a part of the autoionization cascade as the multiply excited projectiles deexcite. We find strong evidence for Coster-Kronig transitions taking place in the hollow atoms which give rise to missing peaks in the Auger spectra.

We report results of one electron capture by highly charged ions colliding with laser excited aligned ${\mathrm{Na}}^{\mathrm{*}}$(3p). The O vi(10\ensuremath{\rightarrow}8) photon emission cross section after electron capture by the ${\mathrm{O}}^{6+}$ projectile is measured in the collision energy range 2-8 keV/amu. Effects of the ${\mathrm{Na}}^{\mathrm{*}}$(3p) orbital alignment on the ) O vi(10\ensuremath{\rightarrow}8) emission are observed and found to be ``reversed'' as compared to the ${\mathrm{He}}^{2+}$\ensuremath{\rightarrow}${\mathrm{Na}}^{\mathrm{*}}$(3p) collision system. Classical trajectory Monte Carlo calculations agree with the measured data and indicate that capture to states with ng10, contributing to the O vi(10\ensuremath{\rightarrow}8) emission via cascades, plays a crucial role in the alignment cross sections.

Experimental evidence is presented for confinement resonances associated with photoabsorption by a Xe atom in a C60 cage. The giant 4d resonance in photoionization of Xe is predicted to be redistributed into four components due to multipath interference of photoelectron waves reflected by the cage. The measurements were made in the photon energy range 60-150 eV by merging a beam of synchrotron radiation with a mass/charge selected Xe@C₆₀+ ion beam. The phenomenon was observed in the Xe@C(58)(3+) product ion channel. [corrected]

Mass-selected beams of atomic ${\mathrm{Ce}}^{q+}$ ions ($q=2$, 3, 4), of ${\mathrm{C}}_{82}^{+}$ and of endohedral $\mathrm{Ce}@{\mathrm{C}}_{82}^{+}$ ions were employed to study photoionization of free and encaged cerium atoms. The Ce $4d$ inner-shell contributions to single and double ionization of the endohedral $\mathrm{Ce}@{\mathrm{C}}_{82}^{+}$ fullerene have been extracted from the data and compared with expectations based on theory and the experiments with atomic Ce ions. Dramatic reduction and redistribution of the ionization contributions to $4d$ photoabsorption is observed. More than half of the Ce $4d$ oscillator strength appears to be diverted to the additional decay channels opened by the fullerene cage surrounding the Ce atom.

Term energies for dielectronic-recombination Rydberg resonances below 0.07 eV are determined for Sc18+ with absolute accuracies below 0.0002 eV by electron collision spectroscopy in an ion storage ring, using the twin-electron-beam technique and a cryogenic photocathode. The lithiumlike 2s_{1/2}-2p_{3/2} transition energy for Z=21 is determined to 4.6 ppm, less than 1% of the few-body effects on radiative corrections. Features from the hyperfine structure of the 2s state could be resolved in the dielectronic-recombination spectrum.

Isotope shifts in dielectronic recombination spectra were studied for Li-like ^{A}Nd^{57+} ions with A=142 and A=150. From the displacement of resonance positions energy shifts \delta E^{142,150}(2s-2p_1/2)= 40.2(3)(6) meV (stat)(sys)) and \delta E^{142,150}(2s-2p_3/2) = 42.3(12)(20) meV of 2s-2p_j transitions were deduced. An evaluation of these values within a full QED treatment yields a change in the mean-square charge radius of ^{142,150}\delta = -1.36(1)(3) fm^2. The approach is conceptually new and combines the advantage of a simple atomic structure with high sensitivity to nuclear size., Comment: 10 pages, 3 figures, accepted for publication in Physical Review Letters

Neutral C60 is well known to exhibit a giant resonance in its photon absorption spectrum near 20 eV. This is associated with a surface plasmon, where delocalized electrons oscillate as a whole relative to the ionic cage. Absolute photoionization cross-section measurements for C+60, C2+60, and C3+60 ions in the 17-75 eV energy range show an additional resonance near 40 eV. Time-dependent density functional calculations confirm the collective nature of this feature, which is characterized as a dipole-excited volume plasmon made possible by the special fullerene geometry.

The 2s(1/2)-2p(1/2) energy splittings DeltaE(L) of the lithiumlike ions 19779Au76+, 20882Pb79+, and 23892U89+ have been measured at the Experimental Storage Ring, utilizing low energy dielectronic recombination. The resonance energies in total 41 different 1s(2) 2p(1/2)nl(j(')) (n > or =20) autoionizing Rydberg states populated in the dielectronic capture process have been determined. The 2s(1/2)-->2p(1/2) excitation energies have been obtained by extrapolation of these resonance energies to the associated series limits n--> infinity. The combined analysis of the experimental data for all three ions yields DeltaE(L)=216.134(96) eV for Au76+, 230.650(81) eV for Pb79+, and 280.516(99) eV for U89+.

Recombination involving the core excitation of two electrons, which may be termed trielectronic recombination, has been experimentally identified for the first time. Using Cl13+ ions circulating in the TSR heavy-ion storage ring, we have observed surprisingly strong low-energy trielectronic recombination resonances, comparable to the dielectronic process. At higher electron-ion collision energies, trielectronic recombination is suppressed due to the autoionization of the triply excited intermediate state into excited final states. The formation of the intermediate state depends sensitively on configuration mixing, making trielectronic recombination a challenge to atomic-structure calculations.

The principle of microscopic time reversal of physical processes, detailed balance, is widely used and depended upon in the theoretical community as a connection between photorecombination (PR) and photoionization (PI). This paper reports on a novel use of detailed balance and the comparison of experimental results obtained by two very distinct techniques to determine both the metastable fraction of an ion beam and partial Sc3+ PR cross sections and partial Sc2+ PI cross sections for the ground state and for two metastable states. The Sc2+ to Sc3+ system presents a unique opportunity to obtain comprehensive state-selective information by combining results from PR and PI experiments.

Dielectronic recombination resonances of $\text{Pb}\text{ }{\text{ }}^{79+}$ associated with $2{s}_{1/2}\ensuremath{\rightarrow}2{p}_{1/2}$ excitations were measured at the heavy-ion storage ring ESR at GSI. The fine structure of the energetically lowest resonance manifold $\text{Pb}\text{ }{\text{ }}^{78+}(1{s}^{2}2{p}_{1/2}20{l}_{j})$ at around 18 eV could partially be resolved, and rate coefficients on an absolute scale were obtained. A comparison of the experimental data with results of a fully relativistic theoretical approach shows that high-angular-momentum components up to $j=31/2$ significantly contribute to the total resonance strength demonstrating the necessity to revise the widespread notion of negligible high-angular-momentum contributions at least for very highly charged ions.