  We present a theoretical study on polarization-averaged molecular-frame
photoelectron angular distributions (PA-MFPADs) emitted from $1s$ orbital of
oxygen atom of dissociating dicationic carbon monoxide CO$^{2+}$. Due to the
polarization-average, contribution of direct wave of photoelectron which has
the biggest contribution to MFPADs is removed, so that PA-MFPADs clearly show
the detail of scattering image of the photoelectron. As a result, it is
necessary to employ well precise theory for the continuum state for the
theoretical analysis. In this study, we applied our Full-potential multiple
scattering theory, where the space is partitioned by using Voronoi polyhedra
and truncated spheres to take into account the electron charge density outside
the physical atomic spheres. We did not use spherical harmonic expansion of the
cell shape functions to avoid convergence problems.The potentials in scattering
cells are prepared employing Multiconfigurational Second-Order Perturbation
Theory Restricted Active Space (RASPT2) method in order to take into account
the influence of core hole in the electron charge density in the final state to
realize realistic relaxation. We showed that the Full-potential treatment plays
an important role for the PA-MFPADs at 100 eV of kinetic energy of
photoelectron. Instead, the PA-MFPADs are not sensitive to type of major
excited state in the Auger final state.We also studied the dynamics of
CO$^{2+}$ dissociation. We found that the PA-MFPADs dramatically change its
shape as a function of C-O bond length.
