FUNNEL STATES AS MEDIATORS OF BORN-OPPENHEIMER BREAKDOWN IN REACTIONSAT AN AVOIDED CROSSING

Accurate quantum dynamics calculations are described for a series of t hree-body model systems exhibiting closely avoided crossings of potent ial energy surfaces in the vicinity of the reaction barrier. In partic ular, the surfaces show avoided crossings of bond-switching diabatic s tates in the vicinity of a saddle point. The dynamics calculations are carried out by linear algebraic variational methods with diabatic ele ctronic basis functions. The coupling of electronically non-adiabatic effects to barrier crossings leads to qualitatively new kinds of quant um effects on the chemical reactivity. We nd strong non-adiabatic effe cts on reaction probabilities due to funnel resonances with weaker eff ects (typically 2-20%) off resonance.