Experimental and theoretical results are reported on double-core excitation and ionization processes in some sulphur containing molecules. X-ray absorption spectra have been recorded at the sulphur K-edge using synchrotron radiation delivered by the DCI ring at LURE (Orsay, France). Absolute x-ray absorption cross sections have been determined for gas phase H 2 S, SO 2 and SF 6 molecules in the 2400-2800 eV region. Several narrow features are observed far from the edge and assigned to 1s −1 2p −1 double-core excited states. Two series of states are present corresponding to the triplet and singlet configurations, due to the core 1s-2p exchange term. The energy, width and intensity of the features are strongly molecule dependent. In the case of H 2 S, a theoretical determination of all the single-and double-core vacancy ionization potentials has been performed using a new theoretical approach which makes it possible to solve the convergence problem inherent in a simple SCF calculation. Results compare favourably with available experimental values. In particular, the singlet-triplet separation is correctly predicted for all the double-core ionized states. The relation between the double-core relaxation energies and the associated single-core relaxation values is discussed. Finally, the double-core excited state energies are determined within a Z + 2 core equivalent model, allowing a full assignment of the 1s −1 2p −1 experimental spectra of H 2 S.
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