Relaxation Dynamics of Naphthalene and 1-Aminonaphthalene in Superexcited States

The relaxation dynamics of naphthalene (NPH) and 1-aminonaphthalene (AMN) in superexcited (SE) states has been investigated by pump-probe femtosecond ionization. SE states were produced by two-photon resonant absorption via S-1 and S-2 states and their time evolution probed by ionization with 800 nm light pulses. A fine-tuning of the pump and probe laser intensities permits us to separate the dynamics of the SE states from that of the S-1/S-2 intermediate states. SE state relaxation pathways were investigated in the channels of the parent and the major fragment ions. The lifetimes of two relaxation processes were derived from the exponential fit and found to be in the femtosecond and the picosecond time scales. The fast component is attributed to internal conversion (IC) from the SE states to the Rydberg states, whereas the slow one, only observed in the fragment transients, is assigned to fragmentation of the relaxed neutral molecules. The study sheds light on the significant role of SE states dynamics in pump-probe ionization experiments.