Study of the mechanism of the N-CO photodissociation in N,N-dimethylformamide by direct trajectory surface hopping simulations.

Photodynamics of N,N-dimethylformamide (DMF) in its low-lying singlet excited n(O)-pi* and pi-pi* states have been explored by the direct trajectory surface hopping method based on multiconfigurational ab initio calculations. The dynamics simulations starting in the first excited singlet state (n(O)-pi*) showed that in 57% of trajectories, S(1) excited DMF decays to the ground via the crossing seam related to the N-CO bond stretching MXS1. In 41% of all trajectories, the relaxation process on the S(1) PES moves the molecule into the minimum, where it stays trapped until the end of simulation time. In simulations starting in the second excited state, all trajectories are found to deactivate through MXS5 (S(2)/S(1)) by very fast N-CO stretching. Because the N-CO dissociation process continues in the S(1) potential energy surface, most of the population overshoots the MXS1 and leads to fully dissociated electronically excited HCO and N(CH(3))(2) radicals. A mechanism for their deactivation by H-C-O and C-N-C bending modes is proposed.