Photoabsorption of Mg above the 3p threshold - art. no. 052716

We present the results of a joint experimental and theoretical study on the absolute photoabsorption cross sections from the ground state leading to r esonance structures between the Mg+ 3p P-2 and Mg+ 4s S-2 thresholds. The a bsolute cross sections are determined by measuring the light attenuation th rough a heatpipe using the synchrotron radiation. The observed spectra are compared and analyzed with the help of a B-spline based multichannel K-matr ix calculation. A hidden 3d4p P-1 resonance missing from the observed spect rum is examined in detail. In addition, a nearly degenerate overlap between 3d5f and 4s 8p P-1 resonances near 77.6 nm is carefully analyzed.