  From a rigorous multichannel quantum-defect formulation of bimolecular
processes, we derive a fully quantal and analytic model for the total rate of
exoergic bimolecular reactions and/or inelastic processes that is applicable
over a wide range of temperatures including the ultracold regime. The theory
establishes a connection between the ultracold chemistry and the regular
chemistry by showing that the same theory that gives the quantum threshold
behavior agrees with the classical Gorin model at higher temperatures. In
between, it predicts that the rates for identical bosonic molecules and
distinguishable molecules would first decrease with temperature outside of the
Wigner threshold region, before rising after a minimum is reached.
