We discuss the role of delocalized states in isomerization dynamics and illustrate the ideas by considering isomerization in HCN. We analyze results from an earlier study, when HCN was treated as a semirigid bender, and isomerization was induced by collision with an Ar atom. That analysis is applied here to three-dimensional HCN, using exact three-dimensional wave functions, obtained using a slight modification of a previous global potential based on high-quality ab initio calculations.