HIGH PRECISION K-SHELL PHOTOABSORPTION CROSS SECTIONS FOR ATOMIC OXYGEN: EXPERIMENT AND THEORY

Photoabsorption of atomic oxygen in the energy region below the 1s super(-1) threshold in X-ray spectroscopy from Chandra and XMM-Newton is observed in a variety of X-ray binary spectra. Photoabsorption cross sections determined from an R-matrix method with pseudo-states and new, high precision measurements from the Advanced Light Source (ALS) are presented. High-resolution spectroscopy with E/ Delta E [asymptotically =] 4250 + or - 400 was obtained for photon energies from 520 eV to 555 eV at an energy resolution of 124 + or - 12 meV FWHM. K-shell photoabsorption cross section measurements were made with a re-analysis of previous experimental data on atomic oxygen at the ALS. Natural line widths [Lambda] are extracted for the 1s super(-1)2s super(2)2p super(4)( super(4)P)np super(3)P[degrees] and 1s super(-1)2s super(2)2p super(4)( super(2)P)n super(3)P[degrees] Rydberg resonances series and compared with theoretical predictions. Accurate cross sections and line widths are obtained for applications in X-ray astronomy. Excellent agreement between theory and the ALS measurements is shown which will have profound implications for the modeling of X-ray spectra and spectral diagnostics.