Photoelectron-photoion-photoion coincidence in Ar dimers

Photoelectron-photoion-photoion coincidence momentum imaging was applied to study 2p photoemission from Ar dimers. We present measurements of the kinetic energy released in fragmentation of Ar₂⁺⁺, angular distributions of energetic fragments, angular distributions of photoelectrons in the laboratory frame and in the molecular frame. The mean kinetic energy of fragment Ar⁺ ions, 2.2 eV, is larger than the value estimated from the Coulomb explosion model with the equilibrium Ar-Ar distance. No significant differences between the photoelectron angular distributions of monomers and dimers can be found in the laboratory frame. The photoelectron angular distributions of dimers in the molecular frame show a minimum for electron emission along the dimer axis at low energies (1.2 and 3.4 eV) and become isotropic at higher kinetic energies.