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.
|Number of pages||7|
|Journal||Journal of physical chemistry|
|Publication status||Published - 1995 Jan 1|
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry