Phys. Chem. Chem. Phys., 2001, 3 (14), 2735 - 2741
DOI: 10.1039/b102053f 

Valley ridge inflection points on the potential energy surfaces 
of H_2S, H_2Se and H_2CO

Wolfgang Quapp, Vladlen Melnikov


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 H_2S and H_2Se 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.