CASPT2, CASSCF and non-adiabatic molecular dynamics (NAMD) studies on the low-lying electronic states of 1H-1,2,3-triazole photolysis

The photolysis mechanisms of 1H-1,2,3-triazole and 1H-1,2,3-benzotriazole were elucidated by employing multiconfigurational methods (CASSCF and CASPT2). The potential energy curves and crossing points for the low-lying excited states were analyzed. In addition to the static electronic structure calculations, non-adiabatic molecular dynamics (NAMD) was propagated at the CASSCF level using SHARC (Surface Hopping including ARbitrary Couplings) dynamics in order to verify the proposed static picture, thereby understanding the possible reaction paths and the time scale of the photo-induced events. The S-1 state for 1H-1,2,3-triazole reached a conical intersection between the S-0 and S-1 surfaces on a time scale of 100 fs. The emerging picture of the reaction presented here is the rupture of the triazole ring in the S-1 state and the relaxation through a conical intersection to the S-0 state. On the S-0 surface, the triazoles easily extrude N-2 and then undergo the hetero-Wolff rearrangement forming ethanimine.