Journal of Molecular Modeling

, Volume 15, Issue 6, pp 701–706 | Cite as

Analysis of diatomic bond dissociation and formation in terms of the reaction force and the position-dependent reaction force constant

  • Jane S. Murray
  • Alejandro Toro-Labbé
  • Tim Clark
  • Peter Politzer
Original Paper


Bond dissociation and formation in diatomic molecules are analyzed in terms of the reaction force F(R) and the reaction force constant κ(R). These were determined for a group of 13 molecules from their extended-Rydberg potential energy functions V(R), which are of near-experimental quality. From F(R) and κ(R) comes a two-stage description of dissociation/formation. In dissociation, the first stage involves stretching of the bond, which is opposed by an increasingly negative retarding force F(R). This reaches a minimum and then begins to weaken in the second stage, which is the transition from stretched molecule to free atoms. Bond formation begins with the reverse transition, driven by a positive F(R) which reaches a maximum for the stretched molecule and then becomes a decreasing restoring force. In the stages in which the system is a stretched molecule, κ(R) is positive with its maximum at the equilibrium bond length; it is zero at the minimum or maximum of F(R), and negative throughout the transition stages, going through a minimum. κ(R) <0 has been found to characterize the transition portion of a reaction. This description of dissociation/formation is reinforced by computed B3LYP and Hartree-Fock force constants at different atom separations for the singlet molecules. Hartree-Fock wave function stability assessments suggest that, for the single-bonded singlet molecules, the onset of electron unpairing in dissociation comes in the neighborhood of the F(R) minimum.


Typical profiles of V(R), the reaction force F(R), and the position-dependent reaction force constant κ(R), (a) – (c) respectively, for the dissociation A−B → A + B


Diatomic molecule dissociation/formation Extended-Rydberg potential energy function Position-dependent reaction force constant Reaction force Wave function stability 



ATL would like to acknowledge the support of Projects FONDECYT #1060590 and #1070590 and Project FONDAP #11980002 (CIMAT).


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Jane S. Murray
    • 1
    • 2
  • Alejandro Toro-Labbé
    • 3
  • Tim Clark
    • 4
    • 5
  • Peter Politzer
    • 1
    • 2
  1. 1.Department of ChemistryUniversity of New OrleansNew OrleansUSA
  2. 2.Department of ChemistryCleveland State UniversityClevelandUSA
  3. 3.Laboratorio de Química Teórica Computacional (QTC), Facultad de QuímicaPontificia Universidad Católica de ChileSantiagoChile
  4. 4.Computer-Chemie-CentrumFriedrich-Alexander-Universität Erlangen-NürnbergErlangenGermany
  5. 5.Interdiscplinary Center for Molecular MaterialsFriedrich-Alexander-Universität Erlangen-NürnbergErlangenGermany

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