Two-photon total annihilation of molecular positronium

The rate for complete two-photon annihilation of molecular positronium Ps₂ is reported. This decay channel involves a four-body collision among the fermions forming Ps₂, and two photons of 1.022 MeV, each, as the final state. The quantum electrodynamics result for the rate of this process is found to be ${\Gamma }_{P{s}_2\to \gamma \gamma }=9.0\times {10}^{-12}{\text{s}}^{-1}$. This decay channel completes the most comprehensive decay chart for Ps₂ up to date. (letter)