where t 0 is a delay time. The overall lifetime of the S 1 state is defined as τ 1 = τ1 + t 0 . The lifetimes of the nπ * (S 1 ) and ππ * (S 2 ) states for trajectories starting in the ππ * state are determined using a two-step irreversible kinetic model. To this aim, we fit the nπ * population (F nπ * ) and ππ * population (F ππ * ) as