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Absolute cross-sections for the K-shell photoionization of Be-like (O4 +) and Li-like (O5 +) atomic oxygen ions were measured for the first time (in their respective K-shell regions) by employing the ion--photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/ΔE ≈ 3200 (≈170 meV, full width at half-maximum) was achieved with photon energy from 550 to 670 eV. Rich resonance structure observed in the experimental spectra is analysed using the R-matrix with pseudo-states (RMPS) method. Results are also compared with the screening constant by unit nuclear charge (SCUNC) calculations. We characterize and identify the strong 1s → 2p resonances for both ions and the weaker 1s → np resonances (n ≥ 3) observed in the K-shell spectra of O4 +. [ABSTRACT FROM AUTHOR]

Measurements of absolute cross sections for the K-shell photoionization of B-like atomic nitrogen ions were carried out utilizing the ion–photon merged-beam technique at the SOLEIL synchrotron radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/ΔE ≈13,500 was the maximum resolution achieved. We have investigated two photon energy regions: 404–409 eV and 439–442 eV. Resonance peaks found in the experimental measured cross sections are compared with theoretical estimates from the multi-configuration Dirac–Fock, R-matrix and empirical methods, allowing identification of the strong 1s → 2p and the weaker 1s → 3p resonances in the observed K-shell spectra of this B-like nitrogen ion. [ABSTRACT FROM AUTHOR]

Absolute and energy scanned cross sections for the electron-impact single ionization of Xeq + (q = 10–17) atomic ions are measured by employing a crossed-beams technique in the collision energy range from threshold to 1000 eV. Direct ionization and indirect excitation-autoionization cross sections are calculated using a configuration-average distorted-wave method for the ground and first same parity excited configuration of the Xeq + (q = 10–17) atomic ions. Both the crossed-beams experiment and distorted-wave theory show a steady decrease in the ionization cross section as the charge of the ion increases. The disagreements between experiment and theory are partly attributed to the many metastable levels of ground and excited configurations found in the ion beam. [ABSTRACT FROM AUTHOR]

Absolute cross sections for the K-shell photoionization of Be-like and Li-like atomic nitrogen ions were measured by employing the ion-photon merged-beam technique at the SOLEIL synchrotron radiation facility in Saint-Aubin, France. High-resolution spectroscopy at nominal resolutions of 38, 56, 111, 133 meV full width at half maximum (FWHM) for Be-like and 125 meV FWHM for Li-like atomic nitrogen ions was achieved for the photon energies ranging from 410 up to 460 eV. The experimental measurements are compared with theoretical estimates from the multi-configuration Dirac-Fock, R-matrix and an empirical method. The interplay between experiment and theory enabled the identification and characterization of the strong 1s → 2p resonances features observed in the K-shell spectra of each ion and the region around 460 eV for the 1s → 3p resonance of the N3+ ion yielding suitable agreement with experiment. [ABSTRACT FROM AUTHOR]

Electron-impact single-ionization cross sections of Snq+ ions in charge states q = 4-13 with 4d[10-(q-4)] outer-shell configurations have been studied in the energy range from the corresponding thresholds up to 1000 eV. Absolute cross sections and fine-step energy-scan data have been measured employing the crossed-beams technique. Contributions of different ionization mechanisms have been analysed by comparing the experimental data with calculations employing the configuration-averaged distorted wave approximation. Ionization plasma rate coefficients inferred from the experimental data are also presented. [ABSTRACT FROM AUTHOR]

Absolute cross sections for the K-shell photoionization of Be-like boron ions were measured with the ion–photon merged-beams technique at the Advanced Light Source synchrotron radiation facility. High-resolution spectroscopy with E/ΔE up to 8800 (ΔE ∼ 22 meV) covered the energy ranges 193.7–194.7 eV and 209–215 eV. Lifetimes of the strongest resonances are determined with relative uncertainties down to approximately 4% for the broadest resonance. The measured resonance strengths are consistent with 60% 1s22s2 1S ground-state and 40% 1s22s2p 3Po metastable-state ions in the primary ion beam and confirmed by comparison with independent absolute photo-recombination heavy-ion storage-ring measurements with B2 + ions using the principle of detailed balance. Experimental determination of the line width for the 1s2s22p 1Po resonance gives a value of 47 ± 2 meV and compares favourably to a theoretical estimate of 47 meV from the R-matrix with pseudo-states (RMPS) method. The measured line widths of the 1s2s2p23P, 3D resonances are 10.0 ± 2 meV and 32 ± 3 meV, respectively, compared to RMPS theoretical estimates of 9 meV and 34 meV. [ABSTRACT FROM AUTHOR]

Absolute cross sections for the K-shell photoionization of boron-like (B-like) O3 + ions were measured by employing the ion–photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/ΔE ≈5000 (≈110 meV, full width half maximum) was achieved with photon energy from 540 up to 600 eV. Several theoretical approaches, including R-matrix, multi-configuration Dirac–Fock and screening constant by unit nuclear charge were used to identify and characterize the strong 1s → 2p and the weaker 1s → 3p resonances observed in the K-shell spectra of this ion. The trend of the integrated oscillator strength and autoionization width (natural line width) of the strong 1s → 2p resonances along the first few ions of the B-like sequence is discussed. [ABSTRACT FROM AUTHOR]

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 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.