title: The reaction force and the transition region of a reaction.
abstract: The reaction force F(R) and the position-dependent reaction force constant kappaF(R) are defined by F(R)=-deltaV(R)/deltaR and kappa(R)=delta2V(R)/deltaR2, where V(R) is the potential energy of a reacting system along a coordinate R. The minima and maxima of F(R) provide a natural division of the process into several regions. Those in which F(R) is increasing are where the most dramatic changes in electronic properties take place, and where the system goes from activated reactants (at the force minimum) to activated products (at the force maximum). Kappa(R) is negative throughout such a region. We summarize evidence supporting the idea that a reaction should be viewed as going through a transition region rather than through a single point transition state. A similar conclusion has come out of transition state spectroscopy. We describe this region as a chemically-active, or electronically-intensive, stage of the reaction, while the ones that precede and follow it are structurally-intensive. Finally, we briefly address the time dependence of the reaction force and the reaction force constant.
authors.affiliation: Laboratorio de Química Teórica Computacional (QTC), Facultad de Química, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Casilla 306, Correo 22, Santiago, Chile. atola@puc.cl
authors.forename: Alejandro
authors.initials: A
authors.lastname: Toro-Labbé
authors.forename: Soledad
authors.initials: S
authors.lastname: Gutiérrez-Oliva
authors.forename: Jane S
authors.initials: JS
authors.lastname: Murray
authors.forename: Peter
authors.initials: P
authors.lastname: Politzer
mesh_terms: D000465:Algorithms; D055598:Chemical Phenomena; D003198:Computer Simulation; D008956:Models, Chemical; D013057:Spectrum Analysis; D013816:Thermodynamics