Reaction force constant and projected force constants of vibrational modes along the path of an intramolecular proton transfer reaction

We have explored the relationships between the reaction force F(ξ), the reaction force constant κ(ξ) and the projected force constants of the intramolecular proton transfer HO−NS → ON−SH along the intrinsic reaction coordinate ξ. The structural changes and energetics associated with the reaction are analyzed in terms of the three regions defined by F(ξ): reactant, transition and product. The significance of the similarity between κ(ξ) and the variation of the force constant associated to the reaction coordinate mode, kξ(ξ), is discussed in detail.