  Theoretical differential oscillator strengths related to monochromatic
opacity due to K- and L-shell absorption from oxygen and iron ions are directly
compared with the Chandra and Xmm-Newton spectra of Seyfert~1 galaxy
MCG--6-30-15. We compute the highly resolved continuum with resonances due to O
I - VI and Fe XVI. It is found that the KLn (n --> infty) resonance series
limits in O VI, and the lowest LMM resonance in Fe XVI, lie at the prominent
17.5 A break in the observed spectra. We also calculate and identify, for the
first time, the observed gap in spectral flux at 22-23 A in the Chandra spectra
due to K --> L resonant absorption features from all O-ions O I - VI,
potentially leading to abundance determination of several or all ionization
stages; similar signature gaps may be predicted due to other elements. The
precise atomic parameters are computed in the relativistic close coupling
approximation using the Breit-Pauli R-matrix method. The new X-ray opacities
might possibly distinguish between models of a dusty warm absorber, and/or
gravitational redshift and broadening due to a massive black hole in
MCG--6-30-15.
