Valley ridge inflection points on the potential energy surfaces of H2S, and H2SeH2CO

TheMP2/6-31G** potential energy surfaces (PES) of the hydrogen sulfide mole cule and of the formaldehyde molecule, as well as the MP2/3-21G** PES of th e hydrogen selenide molecule are used as qualitative models to locate curve s of valley ridge inflection (VRI) points. Crossing points between VRI curv es, or VRI manifolds, and approximations of the reaction path allow the ide ntification of a symmetric bifurcation of an assumed reaction path. The rec ently proposed method of following the reduced gradient is used to calculat e reaction path approximations together with their possible bifurcations. T he VRI points are calculated with the help of Branin's method, the desingul arized global Newton method. The results achieved for the three-atom and H2 S are further extended to the four-atom formaldehyde molecule, being a six- dimensional problem, where H2Se the directions of symmetrical unimolecular isomerization and dissociation are treated. We discuss the significance of VRI curves.