The valence shell photoelectron spectrum of OsO4<\/small> 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) as well as multi-configurational self consistent field (MCSCF) methods. These non-relativistic states when coupled via spin-orbit operator result in the spin-orbit states that are compared with the results from synchrotron measurements. The lowest three cationic states could be described by both EOM-CCSD and MCSCF based methods, whereas the multi-configurational character of the closely spaced fourth and fifth cationic states were suitably described by the latter. The photoelectron spectral intensities of different ionization channels, calculated using the Dyson orbital formalism within sudden approximation, have reproduced the experimental spectrum by capturing all of its essential features, including detailed vibronic structure of the first band that shows the presence of fundamental, overtone and combination bands of a1 and e modes. The kinetic energy dependence of the photoelectron angular distribution parameters, such as, photoionization cross section and asymmetry parameters, have been calculated for each of the photoionization channels and the complex interplay of multiple partial waves that dene the wave function of the ejected electron at different photon energy have been analyzed to explain the resonance structures observed in the experimental cross section profiles.<\/p>")"> Abstract