DOUBLE-CORE IONIZATION AND EXCITATION ABOVE THE SULFUR K-EDGE IN H2S,SO2 AND SF6

Experimental and theoretical results are reported on double-core excit ation 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, Franc e). Absolute x-ray absorption cross sections have been determined for gas phase H2S, SO2 and SF6 molecules in the 2400-2800 eV region. Sever al 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 co re 1s-2p exchange term. The energy, width and intensity of the feature s are strongly molecule dependent. In the case of H2S, a theoretical d etermination of all the single- and double-core vacancy iodization pot entials has been performed using a new theoretical approach which make s it possible to solve the convergence problem inherent in a simple SC F calculation. Results compare favourably with available experimental values. In particular, the singlet-triplet separation is correctly pre dicted for all the double-core ionized states. The relation between th e double-core relaxation energies and the associated single-core relax ation values is discussed. Finally, the double-core excited state ener gies are determined within a Z + 2 core equivalent model, allowing a f ull assignment of the 1s(-1)2p(-1) experimental spectra of H2S.