Funnel states as mediators of Born-Oppenheimer breakdown in reactions at an avoided crossing

Accurate quantum dynamics calculations are described for a series of three-body model systems exhibiting closely avoided crossings of potential energy surfaces in the vicinity of the reaction barrier. In particular, the surfaces show avoided crossings of bond-switching diabatic states in the vicinity of a saddle point. The dynamics calculations are carried out by linear algebraic variational methods with diabatic electronic basis functions. The coupling of electronically non-adiabatic effects to barrier crossings leads to qualitatively new kinds of quantum effects on the chemical reactivity. We find strong non-adiabatic effects on reaction probabilities due to funnel resonances with weaker effects (typically 2–20%) off resonance.