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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]

Dissociative double photoionisation of CO below the adiabatic double ionisation threshold has been studied by the time-of-flight photoelectron–photoelectron coincidence (TOF-PEPECO) and the velocity imaging photoionisation coincidence (VIPCO) methods. By combining the results from the two methods which give complementary information, the double photoionisation process is identified to CO + hv→ CO+* + e− → C+(2P) + [O+(2D/2P)]nl + e− → C+(2P) + O+(4S) + 2e−. The high energy resolution of the TOF-PEPECO spectrometer enables us to resolve individual fragment [O+(2D/2P)]nl states and also intermediate CO+* states. The angular correlations between electrons and ions, deduced from the VIPCO data, imply that the nuclear dissociation is faster or at least comparable in the time scale with molecular rotation, and that the second electron emission occurs after the C+ and O* atoms are far apart. A possible generic identification of the intermediate states is suggested. [Copyright &y& Elsevier]

Photoionization into the dissociation continuum of H2+(X2Σg+) has been studied using the velocity imaging photoionization coincidence method. Asymmetry parameters for the angular distributions of photoelectrons and fragment H+ ions have been measured at photon energies of 21.2, 23.1, 26.9 and 40.8 eV. Molecular frame photoelectron angular distributions (MF-PADs) have also been extracted for the parallel and perpendicular transitions at all the photon energies. All the MF-PADs show p-wave shape, which suggests a dominant p-wave contribution in the photoionization cross-sections at all energies. [Copyright &y& Elsevier]

A coincidence spectrometer combining time-focusing optics with velocity imaging has been developed to achieve high velocity resolution for both positive and negative particles. Positional broadening of particle images and temporal broadening of particle flight times caused by an extended source volume are effectively cancelled by the design of the electrostatic lenses. The performance of the new optics is demonstrated in photoionization of CO. Sample results are presented on dissociative photoionization from CO+(D2Π) and N2O+(C2Σ+), where molecular frame photoelectron angular distributions are obtained for the first time with vibrational resolution of both initial state and diatomic products. [Copyright &y& Elsevier]

Using the velocity imaging photoionization coincidence technique we have determined molecular-frame photoelectron angular distributions for ionization of H2 to the 2pσu, 2sσg and 2pπu states of H2+ from angular correlation between photoelectrons and the product protons. The results are analyzed in terms of electric dipole transitions populating symmetry-allowed low-l partial waves. In perpendicular ionization to 2pσu an almost pure dπg wave is observed, in accordance with simple symmetry predictions. [Copyright &y& Elsevier]