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Abstract: High level electronic structure calculations on the OCS2+ dication made by the spdfg cc-pV5Z/CASSCF/MRCI method are presented. They enable a detailed interpretation of the newly recorded spectra of this ion made by the time-of-flight photoelectron photoelectron coincidence (TOF-PEPECO) method, and provide a reliable basis for analysis of its dissociation pathways. The major dissociation to CO+ +S+ appears to occur not on the ground state surface, but from an excited electronic state. Possible involvement of the CSO2+ isomer in dissociation is discussed. [Copyright &y& Elsevier]

Abstract: The recently discovered emission has been investigated experimentally and theoretically, leading to the identification of two separate fluorescent dicationic transitions ( and 11Δg ←11Δu). The vertical energies of the fluorescent electronic states were directly obtained by detecting photons in coincidence with electron pairs. Their assignment was aided by the use of glass filters to isolate the spectral region of each emission and by performing highly correlated MRCI calculations at a range of geometries. The potential energy curves thus generated predict bound potential energy functions for all linear Σ and Δ states of triplet and singlet spin multiplicities, throughout the energy range studied. Dissociation onsets for different fragmentation pathways are re-evaluated by detecting ions in coincidence with electron pairs. The C+ +S+ onset is revised downwards to 36.8±0.4eV and formation is found to arise from non-statistical dissociation of a limited number of precursor states, which have been identified to be the electronically excited formed in bent structures at these internal energies. Assignments have been attempted for all fragment emissions observed by measuring quantum yields as a function of the selected spectral region. [Copyright &y& Elsevier]

Abstract: The double photoionisation spectrum of molecular iodine has been measured at three wavelengths by the TOF-PEPECO technique and is interpreted using relativistic molecular structure COSCI calculations of potential curves for a large number of electronic states connected to the three lowest groups of dissociation limits. The lowest double ionisation energy is 24.85±0.02eV (adiabatic) or 24.95±0.02eV (vertical). It is associated with the electronic state of . The double ionisation process is mainly direct, and positions and widths of the bands are well reproduced by the calculations. [Copyright &y& Elsevier]

Abstract: Double photoionisation spectra of ethyne and ethyne-d2 have been measured by the TOF–PEPECO technique and by the TPEsCO method with vibrational resolution. With the help of new calculations of the dication structure and Franck–Condon factors we deduce adiabatic double ionisation energies for the first three states of the normal hydrogen isotopomer as 31.74eV (X3Σg-), 32.42 (a1Δg) and 33.07 (b1Σg+). The two techniques give spectra with very different vibrational structure and reasons for the difference are discussed. [Copyright &y& Elsevier]

Abstract: An apparatus for electron–electron-fragment ion triple coincidence experiments has been developed to examine binary (e,2e) scattering reaction in the molecular frame. In the axial recoil limit of fragmentation of the residual ion, measurements of vector correlations among the three charged particles are equivalent to (e,2e) experiments with fixed-in-space molecules. Details and performance of the apparatus are reported, together with preliminary result of collision dynamics study on ionisation–excitation processes of fixed-in-space H2 molecules. We believe that this is the first observation of molecular frame (e,2e) cross sections. [Copyright &y& Elsevier]