Collisional survival of antiprotonic helium atoms Original Research Article

We investigate the collisional survival of antiprotonic p̄He+ atomcules in pure helium from a detailed ab initio analysis of their intermolecular interaction. After averaging over classical p̄ orbits, we attribute the collisional stability of thermalized atomcules to the existence of a high activation barrier due to Pauli repulsion. Our model predicts the reduction of the barrier for outer p̄ orbits, thus accounting for the quenching of high n states by He atoms. We also investigate the thermalization stage of newly formed atomcules from a classical trajectory Monte Carlo approach. Our results support the destruction of the states with n⩾41, as well as the strong depopulation of all n<41 layers, with a quenching rate of 50% at least. Assuming a statistical distribution of newly formed atomcules with respect to their initial angular momentum, we account for the 3% observed trapping fraction of metastable states.