THEORETICAL-STUDY OF THERMAL-DECOMPOSITION OF AZOMETHANE

Thermal one- and two-bond dissociation processes of cis- and trans-azo methane were studied by ab initio computation with DZP and TZ2P basis sets, using the d(N-C) bond lengths as the reaction coordinates. The g eometries were optimized at the MP2 level, and the dissociation energi es obtained exploiting a single-point, fourth-order Moller-Plesset cal culations [MP4SDTQ/TZ2P]. At this level of theory including zero-point energies, the trans-isomer is by 9.3 kcal/mol more stable than the ci s-isomer. The results show that the energetically more favourable one- bond cleavage proceeds without transition state with the predicted bon d dissociation energy D-0 of 47.8 kcal/mol for trans-azomethane and 38 .5 kcal/mol for cis-azomethane. With calculated barrier heights the un imolecular dissociation rate constants have been determined by means o f the RRKM theory. The second-order saddle points localized for synchr onous decomposition pathways lie 13 (trans)-23(cis) kcal/mol above the one-bond dissociation energies [MP2/DZP].