Quantum theory of reactive collisions for 1/r^n potentials

We develop a general quantum theory for reactive collisions involving power-law potentials (-1/r^n) valid from the ultracold up to the high-temperature limit. Our quantum defect framework extends the conventional capture models to include the non-universal case when the short-range reaction probability P^{re} < 1. We present explicit analytical formulas as well as numerical studies for the van der Waals (n = 6) and polarization (n = 4) potentials, and relate our work to recent merged beam experiments on Penning ionization for collision energies below 0.1 meV [Henson et al, Science 338, 234(2012)].