Corner-cutting tunneling

These approximations include corner-cutting tunneling. Corner cutting means that the tunneling path is shorter than the minimum energy path. 

When 2Qpv/cob < 1, we are in the fast-flip , or sudden approximation , or corner-cutting , or large curvature limit, where the reaction coordinate follows theMEP, but before it reaches the saddle point it tunnels along the s coordinate in a time that is short compared to the timescale of the Q vibration. 

Reaction path curvature is actually a vector with 3N — 7 components [80]. Each component is associated with a particular generalized normal mode, and it measures the extent to which the system curves into a particular direction as it progresses along the MEP. Corner-cutting tunneling involves a coupled motion involving the reaction coordinate and all the generalized normal modes that are associated with nonzero curvature components [81]. 

Figure 14.1 A contour plot illustration of the "corner cutting" tunnelling path...

A reaction may proceed far away from the course of a static defined RP. It is well known that the preferential path may not only deviate from the RP by tunneling induced corner cutting (for Refs.see 20a, cf. additionally Ref.20Jb) but also by vibrationally induced corner cutting (Ref. 21). Model systems (for example F+ DBr(v) FD + Br) demonstrate this important role of reaction dynamics in comparison with static properties of conventionally defined RPs (Ref.20a). 

Chem. Soc., IIS, 7806 (1993). Direct Dynamics Calculation of the Kinetic Isotope Effect for an Organic Hydrogen-Transfer Reaction, Including Corner-Cutting Tunneling in 21 Dimensions. 

---