Theoretical study of thermal decomposition of azomethane

Abstract

Thermal one- and two-bond dissociation processes ofcis- andtrans-azomethane were studied byab initio computation with DZP and TZ2P basis sets, using thed(N-C) bond lengths as the reaction coordinates. The geometries were optimized at the MP2 level, and the dissociation energies obtained exploiting a single-point, fourth-order Moller-Plesset calculations [MP4SDTQ/TZ2P]. At this level of theory including zero-point energies, thetrans-isomer is by 9.3 kcal/mol more stable than thecis-isomer. The results show that the energetically more favourable one-bond cleavage proceeds without transition state with the predicted bond dissociation energyDo of 47.8 kcal/mol fortrans-azomethane and 38.5 kcal/mol forcis-azomethane. With calculated barrier heights the unimolecular dissociation rate constants have been determined by means of the RRKM theory. The second-order saddle points localized for synchronous decomposition pathways lie 13 (trans)-23(cis) kcal/mol above the one-bond dissociation energies [MP2/DZP].