Double photoionization accompanied by loss of n C atoms (n = 0, 2, 4, 6) was investigated by merging beams of Xe@C + 60 ions and synchrotron radiation and measuring the yields of product ions. The giant 4d dipole resonance of the caged Xe atom has a prominent signature in the cross section for these product channels, which together account for 6.2 ± 1.4 of the total Xe 4d oscillator strength of 10. Compared to that for a free Xe atom, the oscillator strength is redistributed in photon energy due to multipath interference of outgoing Xe 4d photoelectron waves that may be transmitted or reflected by the spherical C + 60 molecular cage, yielding so-called confinement resonances. The data are compared with an earlier measurement and with theoretical predictions for this single-molecule photoelectron interferometer system. Relativistic R-matrix calculations for the Xe atom in a spherical potential shell representing the fullerene cage show the sensitivity of the interference pattern to the molecular geometry.
7An analytical formula is developed to represent accurately the photoabsorption cross section of O I for all energies of interest in X-ray spectral modeling.In the vicinity of the K edge, a Rydberg series expression is used to fit R-matrix results, including important orbital relaxation effects, that accurately predict the absorption oscillator strengths below threshold and merge consistently and continuously to the above-threshold cross section. Further minor adjustments are made to the threshold energies in order to reliably align the atomic Rydberg resonances after consideration of both experimental and observed line positions. At energies far below or above the K-edge region, the formulation is based on both outer-and inner-shell direct photoionization, including significant shakeup and shake-off processes that result in photoionization-excitation and double photoionization contributions to the total cross section. The ultimate purpose for developing a definitive model for oxygen absorption is to resolve standing discrepancies between the astronomically observed and laboratory measured line positions, and between the inferred atomic and molecular oxygen abundances in the interstellar medium from xstar and spex spectral models.Subject headings: X-rays: ISM -ISM: atoms -atomic processes -line: formation -8 line: profiles 9 Atomic photoionization, an important astrophysical process, has been studied for 11 more than a century since the seminal understanding of its energetics by Einstein (1905) 12 and the first calculations of quantum mechanical cross sections (Bates 1939). Over the 13 years, a plethora of experimental and theoretical investigations have managed an excellent 14 grasp of its physics (Fano & Cooper 1968; Starace 1982), together with a remarkable 15 quantitative description of the valence-shell photoionization of atoms and atomic ions 16 (Opacity Project Team 1995, 1997). However, the quantitative model of inner-shell 17 photoabsorption is less sound due to a variety of relaxation processes, namely Auger and 18 X-ray emission, that must be taken into account in order to achieve acceptable accuracy, 19 especially in the near-threshold region. 20 Inner-shell photoabsorption of metals with nuclear charge 7 ≤ Z ≤ 28 is directly 21 accessible to modern X-ray observatories such as Chandra and XMM-Newton, and, hence, 22 is of much interest in astronomy. Particularly prominent in the photoabsorption of the 23 interstellar medium (ISM) are the K-shell features (lines and edges) of atomic oxygen, 24 which is the most abundant metal and is critically important in the energetic and chemical 25 evolution of the Universe (Stasińska et al. 2012). At present, though, the unsatisfactory 26 quantitative understanding of oxygen inner-shell photoabsorption is such that there exists 27 various sets of cross sections, each one leading to different conclusions regarding the 28 ionization and atomic-to-molecular fractions in the ISM along various Galactic lines of 29 sight. 30 The first inner-shell photoabsorption cross se...
K-shell photoabsorption cross sections for the isonuclear C I -C IV ions have been computed using the R-matrix method. Above the K-shell threshold, the present results are in good agreement with the independent-particle results of Reilman & Manson (1979). Below threshold, we also compute the strong 1s → np absorption resonances with the inclusion of important spectator Auger broadening effects. For the lowest 1s → 2p, 3p resonances, comparisons to available C II, C III, and C IV experimental results show good agreement in general for the resonance strengths and positions, but unexplained discrepancies exist.Our results also provide detailed information on the C I K-shell photoabsorption cross section including the strong resonance features, since very limited laboratory experimental data exist. The resultant R-matrix cross sections are then used to model the Chandra X-ray absorption spectrum of the blazar Mkn 421.
We demonstrate serious misrepresentation of existing experimental data and important omissions in the List of references in the paper [1]. We demonstrate that what is called in [1] total photoionization cross-section is in fact a partial photoionization crosssection. We demonstrate that long before [1] and presented there experimental data for photoionization of 60 @ Xe C + were obtained, a theoretical prediction for 60
The effects of endohedral confinement on the correlation energy of Be, Mg, and Ca atoms have been investigated using modified Hartree-Fock (HF) and multiconfiguration Hartree-Fock (MCHF) methods where the endohedral system (A@C60) is approximated as an atom enclosed in an attractive spherically symmetric potential well of inner radius r ∼ 5.8 a.u. and thickness of ∆ ∼ 1.89 a.u., and correlation energies are studied as a function of the depth of the confining potential (0 ≤ U0 ≤ 1 a.u.) to give some idea as to how the correlation energy behaves in different endohedral environments. In general, we have found that, as a function of well depth, starting from the free atom, valence electrons diffuse outward, in the presence of the confining potential, which causes the electrons to be further apart, thereby decreasing the correlation energy; however, with further increase of well depth, the valence electrons become trapped in the confining well and, as a result of their being closer together, the correlation energy increases.
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