Comparison of internal conversion dynamics of azo and azoxy energetic moieties through the (S1/S0)CI conical Intersection: An ab initio multiple spawning study

We have explored the nonadiabatic chemical dynamics of trans-azomethane (AM) and azoxymethane (AOM) using ab initio multiple spawning (AIMS) simulation and CASSCF theory. A trans-to-cis isomerization around the N = N bond and a pyramidalization of the N(O)=N moiety are predicted to be involved in the internal conversion process of AM and AOM molecules, respectively. AIMS-based simulation at the CASSCF(6,4)/6-31G(d) level of theory reveals that electronically excited AM and AOM molecules undergo extremely fast (approximately in 125 fs for AM and 64 fs for AOM) relaxation to the ground state via the (S-1/S-0)(CI) conical intersection. In addition, AIMS simulation at the CASSCF(10,8)/6-31G(d) level of theory reveals that AM molecules exhibit two relaxation pathways: major (comprising 75%) channel involves an isomerization process and minor (comprising 25%) channel features the C-N bond dissociation.