Photoabsorption and subsequent decay of Na and Mg atoms in the 2s–np autoionizing resonance region

Abstract

Photoabsorption and subsequent decay of Na and Mg atoms have been studied experimentally in the vicinity of the 2s excitation region. The charge-separated photoion-yield method using monochromatized synchrotron radiation was employed to detect the resonance excitation features separately in the single and double ionization channels. The photoion-yield spectrum of each atomic species consists of asymmetric features from the 2s−1np autoionizing resonance series below the 2s ionization limit and several weak features from the 2s−13s−1npn′s shake-up processes above the ionization limit. The observed resonances were analysed by multi-configuration Dirac–Fock calculation and by least-squares fitting to the Beutler–Fano profile. The decay processes of the resonance states are discussed. The Na 2s−13p resonance can end up with Na2+ ions by one-step double autoionization with branching ratio about 0.05.