Simulation of the photodeactivation of formamide in the nO-π* and π-π* states:: An ab initio on-the-fly surface-hopping dynamics study

The short-time photodynamics (1 ps) of formamide in its low-lying singlet excited n(O)-pi(*) and pi-pi(*) states have been investigated by the direct trajectory surface-hopping method based on multiconfigurational ab initio calculations. The simulations showed that in both states, the primary deactivation process is C-N bond dissociation. In the ground state, the energy is transferred to (a) translational motion of the HCO and NH2 fragments, (b) additional C-H dissociation from the vibrationally hot HCO fragment, or (c) formation of NH3 and CO. In addition to the C-N dissociation pathway, C-O bond fission is found to be an additional primary deactivation path in the pi-pi(*) dynamics. From fractional occupations of trajectories, lifetimes of formamide were estimated: tau(S-1)=441 fs and tau(S-2)=66 fs.