Anti-Arrhenius behaviour in positronium chemistry: a Kramersʹ turnover?

The observed anti-Arrhenius temperature dependence of the rate for positronium–acceptor (Ps–Ac) complex formation above, and a normal Arrhenius behaviour below, a solvent-dependent critical temperature T0, is argued to be ascribable to a Kramersʹ turnover, relating to viscosity effects unleashed by temperature-dependent surface tension, in the context of the bubble model of the positronium atom in liquids, provided one uses a more realistic and robust version thereof developed by us, which is also in closer accord with lifetime and gamma–gamma angular correlation data in pure solvents.