Approximate Time Independent Methods for Polyatomic Reactions

In this chapter I review approximation methods to describe the quantum reactive scattering of polyatomic molecules. These methods are known generically as “reduced dimensionality” approximations. I will review several versions of this method, and focus on the so-called J-shifting approximation and very recent developments of it. These new developments are reviewed for the OH + H₂reaction, where apparent discrepancies between coupled-states and standard J-shifting rate constants are resolved. I also present new expressions in the spirit of J-shifting for reactions that proceed via complex formation.