Mechanism of the thermal decomposition and the (n-π*) excited states of azomethane

C. H. Hu, H. F. Schaefer

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The mechanism of azomethane decomposition CH3N=NCH3 → 2CH3· + N2 has been investigated with ab initio quantum mechanical approaches. The methods include self-consistent field (SCF), two-reference SCF (TCSCF), single- and double-excitation configuration interaction (CISD), two-reference CISD with TCSCF optimized molecular orbitals (TCSCF-CISD), single- and double-excitation coupled cluster (CCSD), and the single-, double-, and perturbative triple-excitation coupled cluster [CCSD(T)]. The `synchronous' decomposition pathway, in which a transition state of two equal distance C-N bonds is involved, was shown to be infeasible. Both cis- and trans-azomethane break one C-N bond at the first step and form the CH3 and CH3N2 radicals; then the methyldiazenyl radical further decomposes into CH3 and N2. The first C-N bond of cis- and trans-azomethane breaks without a transition state, with the predicted D0 of 46.3 kcal/mol for trans-azomethane at the TZ2P CCSD(T) level. CH3N2 decomposes through a barrier of nearly 2.3 kcal/mol into CH3 and N2, as reported by the authors previously. cis-Azomethane was predicted to be about 9.1 kcal/mol higher in energy than trans-azomethane [TZ2P CCSD(T)]. The first n → π* excited singlet (S1) and triplet (T1) states were studied also, and we report the geometries, predicted vibrational frequencies, and energetics for the vertical and adiabatic transitions of these states.

Original languageEnglish
Pages (from-to)7507-7513
Number of pages7
JournalJournal of physical chemistry
Issue number19
Publication statusPublished - 1995 Jan 1

All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Physical and Theoretical Chemistry

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