Double-core ionization and excitation above the sulphur K-edge in , and

Abstract

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.

Spin-orbit relativistic calculations of the core excitation spectra of SO2

“…6,7 The experimental spectrum below edge presents two well separated and intense features at lower energy associated with the valence transitions followed by weaker peaks ascribed to Rydberg excitations which are, however, still subject to some uncertainties due to an incomplete resolution even in the high resolution photoabsorption spectra. 6 The calculated spectrum compares very well with the experiment and shows that the Rydberg region is contributed by a large number of lines very close in energy on going towards the ionization limit. The dipole allowed excitations are possible from the S 1s͑a 1 ͒ orbital to final orbitals with a 1 , b 1 , and b 2 symmetries and the calculated oscillator strength f maps the sulfur p content of the final orbitals.…”

“…[5][6][7][8][9][10][11] In particu-lar, for the S 2p threshold the experiment 10 has allowed to resolve a variety of Rydberg states in a region where the spin-orbit splitting as well as the molecular field splitting are responsible for a high level of complexity in the attribution of the excited states. The core excitations in SO 2 provide a good test for the theory because the inner-shell spectra relative to the three core edges S 1s, S 2p, and O 1s have been the object of numerous experimental investigations some of them at high level of resolution.…”

Molecular double core hole electron spectroscopy for chemical analysis

“…The chemical shifts of one-atomic site DIPs, or briefly one-site DIPs, were found to be similar to the chemical shifts of the single core level ionization potentials (IPs), or ionization energies (IEs). This finding has given impetus to a number of theoretical studies aimed at elucidating properties of molecular double core hole states [4][5][6][7] .…”

Inner-shell single and double ionization potentials of aminophenol isomers

“…In contrast, doubly ionized states with core vacancies on different atomic centers and the respective DIPs are noticeably more sensitive to the chemical environment than the single and one-site double IPs as shown by Cederbaum et al 17,18 This fact gave rise to a number of subsequent studies aimed at clarifying different aspects of double core ionization and properties of two-site DIPs. [19][20][21][22] The interest in this subject, however, faded away because experimental techniques capable of measuring two-site DIPs were not available at that time.…”