Rare decays of the positronium ion and molecule, $\text{Ps}^{-}\to e^{-}γ$ and $\text{Ps}_{2}\to e^{+}e^{-}γ,~γγ,~e^{+}e^{-}$
Decay rates of the positronium molecule $\text{Ps}_{2}$ into two photons and into an electron-positron pair are determined. Previous studies find that these rates are very different, \[ Γ\left(\text{Ps}_{2}\to e^{+}e^{-}\right)/Γ\left(\text{Ps}_{2}\toγγ\right)\simeq250\text{ (previous studies)}. \] This is puzzling since both processes have two body final states and are of the same order in the fine structure constant. We propose a simple calculational method and test it with the well-established decay of the positronium ion into an electron and a photon. We then employ it to correct predictions for both these $\text{Ps}_{2}$ decays. We find that previous studies overestimated the $e^{+}e^{-}$ and underestimated the $γγ$ channel by factors of about 5.44 and 3.93 respectively. Our results give $Γ\left(\text{Ps}_2\to e^+e^-\right)/Γ\left(\text{Ps}_2 \to γγ\right) \simeq 11.7$.