Valley ridge inflection points on the potential energy surfaces of H2S, H2Se and H2CO

Abstract

The MP2/6-31G** potential energy surfaces (PES) of the hydrogen sulfide molecule and of the formaldehyde molecule, as well as the MP2/3-21G** PES of the hydrogen selenide molecule are used as qualitative models to locate curves of valley ridge inflection (VRI) points. Crossing points between VRI curves, or VRI manifolds, and approximations of the reaction path allow the identification of a symmetric bifurcation of an assumed reaction path. The recently proposed method of following the reduced gradient is used to calculate reaction path approximations together with their possible bifurcations. The VRI points are calculated with the help of Branin's method, the desingularized global Newton method. The results achieved for the three-atom H₂S and H₂Se are further extended to the four-atom formaldehyde molecule, being a six-dimensional problem, where the directions of symmetrical unimolecular isomerization and dissociation are treated. We discuss the significance of VRI curves.