A significant role of the totally symmetric valley-ridge inflection point in the bifurcating reaction pathway

Appearance of the valley-ridge inflection (VRI) point on the intrinsic reaction path (IRP) introduces geometrical instability of the reaction coordinate and sometimes leads to two different product minima on the potential energy surface (PES). A significant role of the totally symmetric VRI point on the IRP is discussed from the viewpoint of branching of the reaction pathway. As illustrative examples, ab initio calculations were performed to determine the IRP for XCHO^??+?CH₃Cl (X?=?H, CH₃) at the M?ller?CPlesset second-order perturbation theory (MP2) level with 6-31+G(d) basis sets and geometric features of the PES around the IRP have been analyzed.