330 research outputs found
Photoionization of tungsten ions: experiment and theory for W
Experimental and theoretical results are reported for single-photon single
ionization of the tungsten ion W. Absolute cross sections have been
measured employing the photon-ion merged-beams setup at the Advanced Light
Source in Berkeley. Detailed photon-energy scans were performed at 200~meV
bandwidth in the 40 -- 105~eV range. Theoretical results have been obtained
from a Dirac-Coulomb R-matrix approach employing basis sets of 730 levels for
the photoionization of W. Calculations were carried out for the
, =2, ground level and the
associated fine-structure levels with =3 and 4 for the W ions. In
addition, cross sections have been calculated for the metastable levels
. Very satisfying agreement of theory and experiment is
found for the photoionization cross section of W which is remarkable
given the complexity of the electronic structure of tungsten ions in low charge
states.Comment: 15 pages, 3 figures, to appear in the Journal of Physics B: Atomic,
Molecular and Optical Physic
Recommended from our members
Polarization control at the microscopic and electronic structure observatory
The new Microscopic and Electronic Structure Observatory (MAESTRO) at the Advanced Light Source (ALS) in Berkeley provides X-rays of variable polarization, produced by an elliptically polarized undulator (EPU), for angle resolved photoemission (ARPES) and photoemission electron microscopy (PEEM) experiments. The interpretation of photoemission data, in particular of dichroism effects in ARPES, requires the precise knowledge of the exact polarization state. Numerical simulations show that the first harmonics of the EPU at MAESTRO provides soft X-rays of almost 100% on axis polarization. However, the higher harmonics as well as the downstream optical elements of the beamline, have a considerable impact on the polarization of the light delivered to the experimental end-station. Employing a simple reflective polarimeter, the polarization is characterized for variable EPU and beamline settings and the overall degree of polarization in the MAESTRO end-stations is estimated to be on the order of 83%
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 , =1/2, ground level and the associated
excited metastable levels with =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}, =5/2, and for
the F term, 5d^3 6s^2 \; ^4{\rm F}_{J}, with = 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
Recommended from our members
Absolute single photoionization cross-sections of Br3+: Experiment and theory
Absolute single photoionization cross section measurements for Br3+ ions are reported in the photon energy range 44.79-59.54 eV at a photon energy resolution of 21 ±3 meV. Measurements were performed at the Advanced Light Source at Lawrence Berkeley National Laboratory using the merged-beams technique. Numerous resonance features in the experimental spectrum are assigned and their energies and quantum defect values are tabulated. The cross-section measurements are also compared with Breit-Pauli R-matrix calculations with suitable agreement over the photon energy range investigated. Analysis of the measured spectrum including Rydberg resonance series identifications produced a new emperical determination of the ionizational potential of Br3+ of 46.977 ± 0.050 eV, which is 805 meV lower than the most recently published value of 47.782 eV. This disparity between our determination and the earlier published value is similar to an 843 meV shift in the accepted ionization potential published for iso-electronic Se2+ as part of this same research program
The structure of Cu(110) (2×3)–N; pseudo‐square reconstruction of a rectangular mesh substrate
The structure of the Cu(110)(2×3)–N phase has been investigated by parallel studies using 3‐keV Li+ and 2‐keV He+ion scattering and scanned energy mode normal emission N 1s photoelectron diffraction. The Li+ion scattering results provide clear evidence for anadsorbate‐induced reconstruction of the Cu surface and, in particular, indicate a shortening of the Cu–Cu atomic spacing along the 〈100〉 azimuth to a value of 2.7±0.1 Å, similar to the 〈110〉 spacing of 2.55 Å. A model of the surface consistent with this result involves a pseudo‐square Cu top atom layer with N atoms occupying alternate hollow sites leading to a local structure which is a 6% distorted Cu(100)c(2×2)–N phase. He+ion scattering data provides support for the N hollow adsorption sites. Scanned energy mode photoelectron diffraction is insensitive to the nature of the reconstruction but provides information on the local adsorption sites and, hence, on the lateral registry of the reconstructed overlayer and the underlying substrate
Recommended from our members
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
- …