Theoretica chimica acta

, Volume 66, Issue 3–4, pp 217–232 | Cite as

Dissociation of diimide

  • Ulf Brandemark
  • Per E. M. Siegbahn


Parts of the potential energy surface of N2H2 have been studied using CASSCF- and contracted CI-methods. Of particular interest was the concerted dissociation of cis- and trans-diimide into N2 and H2, since the trans-dissociation is symmetry allowed and the cis-dissociation forbidden. Three different saddle points were located, of which only one, of C- symmetry, is a true transition state. Elaborate numerical gradient methods using exact Hessians and update procedures had to be used to find these saddle points on the unexpectedly complex N2H2-surface. The barrier height with respect to trans-diimide is 61 kcal/mol after vibration correction. Since this energy is higher than the barrier for interconversion, cis- and trans-diimide have the same transition state. It is further found that diimide preferably dissociates stepwise, by losing one hydrogen at a time, rather than in a concerted way. This conclusion is drawn basically because the geometry of the transition state for the concerted dissociation has a very long H-H distance of 5.6 a.u. The N-H bond energy in trans-diimide is 56 kcal/mol after vibration correction.

Key words

Diimide dissociation of ∼ 


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Copyright information

© Springer-Verlag 1984

Authors and Affiliations

  • Ulf Brandemark
    • 1
  • Per E. M. Siegbahn
    • 1
  1. 1.Institute of Theoretical PhysicsUniversity of StockholmStockholmSweden

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