Numerical Simulations of Single Photon Double Ionization of the Helium Dimer

We study the energy exchange via electron correlation upon photon absorption over large distances in double photoionization of the helium dimer. Results of numerical simulations of the interaction of a planar helium dimer model with a short light pulse are found to be in good agreement with recent experimental data for the angular distribution of the emitted electron. The double ionization probability is closely related to that of the photoemission of an electron from one of the helium atoms along the internuclear axis. This provides direct evidence for the knockoff mechanism by which the photon energy is shared between the electrons over distances of several Angstroms in the dimer. Furthermore, our simulations are able to visualize the knockoff process as a function of time.