Correlation effects in the photoelectron spectrum and photoionization dynamics of OsO₄

The valence shell photoelectron spectrum of OsO4 has been calculated from the wave functions of the ejected photoelectrons responsible for the formation of the lowest five cationic states, whose vertical ionization energies have been estimated using the equation of motion coupled cluster with singles and doubles (EOM-CCSD) and multi-configurational self consistent field (MCSCF) based methods. These non-relativistic states when coupled via the spin-orbit operator result in the spin-orbit states, which are compared with the results from synchrotron measurements. The lowest three cationic states could be described by both the EOM-CCSD and MCSCF based methods, whereas the multi-reference character of the closely spaced fourth and fifth cationic states was suitably described by the latter method. The photoelectron spectral intensities of different ionization channels, calculated using the Dyson orbital formalism within the sudden approximation, reproduced the experimental spectrum by capturing all of its essential features, including the detailed vibronic structure of the first band, which shows the presence of fundamental, overtone and combination bands of a1 and e modes. The kinetic energy dependence of the photoionization parameters, such as the photoionization cross section and asymmetry parameters, has been calculated for each of the photoionization channels and the complex interplay of multiple partial waves that define the wave function of the ejected electron at different photon energies has been analyzed to explain the resonance structures observed in the experimental cross section profiles.