  We consider a general problem of inelastic collision of particles interacting
with power-law potentials. Using quantum defect theory we derive an analytical
formula for the energy-dependent complex scattering length, valid for arbitrary
collision energy, and use it to analyze the elastic and reactive collision
rates. Our theory is applicable for both universal and non-universal
collisions. The former corresponds to the unit reaction probability at short
range, while in the latter case the reaction probability is smaller than one.
In the high-energy limit we present a method that allows to incorporate quantum
corrections to the classical reaction rate due to the shape resonances and the
quantum tunneling.
