Single-photon single ionization of W+^{+} ions: experiment and theory

Experimental and theoretical results are reported for photoionization of Ta-like (W$^{+}$) tungsten ions. Absolute cross sections were measured in the energy range 16 to 245 eV employing the photon-ion merged-beam setup at the Advanced Light Source in Berkeley. Detailed photon-energy scans at 100 meV bandwidth were performed in the 16 to 108 eV range. In addition, the cross section was scanned at 50 meV resolution in regions where fine resonance structures could be observed. Theoretical results were obtained from a Dirac-Coulomb R-matrix approach. Photoionization cross section calculations were performed for singly ionized atomic tungsten ions in their $5s^2 5p^6 5d^4({^5}D)6s \; {^6}{\rm D}_{J}$, $J$=1/2, ground level and the associated excited metastable levels with $J$=3/2, 5/2, 7/2 and 9/2. Since the ion beams used in the experiments must be expected to contain long-lived excited states also from excited configurations, additional cross-section calculations were performed for the second-lowest term, 5d^5 \; ^6{\rm S}_{J}, $J$=5/2, and for the $^4$F term, 5d^3 6s^2 \; ^4{\rm F}_{J}, with $J$ = 3/2, 5/2, 7/2 and 9/2. Given the complexity of the electronic structure of W$^+$ the calculations reproduce the main features of the experimental cross section quite well.Comment: 23 pages, 7 figures, 1 table: Accepted for publication in J. Phys. B: At. Mol. & Opt. Phy

Secondary ion mass spectrometry and x-ray absorption near-edge structure spectroscopy of isotopically anomalous organic matter from CR1 chondrites GRO 95577

We located interstellar organics from a CR1 chondrite with NanoSIMS and analyzed FIB-extracted sections with XANES. D-rich material appears not associated with a functional group, whereas 15N-rich matter shows some affinity to nitrile functionality

Advances in Atomic Data for Neutron-Capture Elements

Neutron(n)-capture elements (atomic number Z>30), which can be produced in planetary nebula (PN) progenitor stars via s-process nucleosynthesis, have been detected in nearly 100 PNe. This demonstrates that nebular spectroscopy is a potentially powerful tool for studying the production and chemical evolution of trans-iron elements. However, significant challenges must be addressed before this goal can be achieved. One of the most substantial hurdles is the lack of atomic data for n-capture elements, particularly that needed to solve for their ionization equilibrium (and hence to convert ionic abundances to elemental abundances). To address this need, we have computed photoionization cross sections and radiative and dielectronic recombination rate coefficients for the first six ions of Se and Kr. The calculations were benchmarked against experimental photoionization cross section measurements. In addition, we computed charge transfer (CT) rate coefficients for ions of six n-capture elements. These efforts will enable the accurate determination of nebular Se and Kr abundances, allowing robust investigations of s-process enrichments in PNe.Comment: To be published in IAU Symp. 283: Planetary Nebulae, an Eye to the Future; 2 page

Angle-resolved photoelectron spectroscopy of the core levels of N_2O

We have measured photoionization cross sections and photoelectron asymmetry parameters for each of the core levels of N_2O. We have also carried out frozen‐ and relaxed‐core Hartree–Fock studies of these cross sections so as to better understand the underlying shape resonant structure and the role of electronic relaxation in these processes. A broad shape resonance is observed in each of the core‐hole cross sections at 10‐20 eV kinetic energy and there is some evidence of a second shape resonance near the thresholds, an energy region which is not accessible experimentally. The cross sections also exhibit site‐specific behavior with maxima at widely separated photoelectron kinetic energies. These differences probably arise from the fact that photoelectron matrix elements for different core orbitals probe different regions of the shape resonant orbital which extends over the entire molecule. Although the higher energy shape resonances appear quite similar, Hartree–Fock studies show that the central nitrogen resonance is more sensitive to effects of electronic relaxation than the terminal nitrogen or oxygen resonances. Large differences are also seen between the photoelectron asymmetry parameters for the central and terminal atoms

Significant Redistribution of Ce 4\u3ci\u3ed\u3c/i\u3e Oscillator Strength Observed in Photoionization of Endohedral Ce@C+82 Ions

Mass-selected beams of atomic Ceq+ ions (q = 2, 3, 4), of C+82 and of endohedral Ce@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 Ce@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