A model is developed which can be used to understand how collision geometry can dictate product state lambda doublet ratios in direct bimolecular reactions that produce diatomic products in a Pi molecular energy state. The predicted lambda doublet ratio is A'/A"=2 for unconstrained collision geometry, while the two limiting case geometries of exclusive end-on collisions and exclusive side-on collisions yield lambda doublet ratios of A'/A"=infinity and A'/A"=1, respectively. The theory is derived and used to interpret the experimental lambda doublet ratio of OH (v=0) from the H+N2O-->OH+N-2 reaction.