Exploring potential energy surfaces around valley-ridge inflection points

Purpose: Valley-ridge inflection (VRI) points play an important role in organic chemistry, especially in post-TS bifurcations. We explain a new discovery of a special structure of the region with another type of VRI point. Methods: We apply the theory of Newton trajectories (NTs) and gradient extremals (GEs) to cases of two dimensional potential energy surfaces. Results: We have found a case where the VRI of a new type is traversed by a quasi-regular NT, a semi-singular one, so to speak. Here, the gradient is the eigenvector to zero eigenvalue. Conclusion: The new type of VRI point is connected with a 'dead' valley of the PES. The example is a nice demonstration that the index theorem for NTs holds, nevertheless. NTs and GEs are important tools to explore the region of a VRI point.