Photodissociation Dynamics of Ortho and Meta Fluorophenols: The Origin of Fast Protons

A recent experimental study with time-resolved velocity map imaging demonstrated that the total kinetic energy release spectra obtained from photodissociation of ortho and meta fluorophenols have distinct features after excitation into the origin of the S₁ state. A peak at 6000 cm^-1 was observed for both molecules, while another at 13000 cm^-1 dominates the spectrum of ortho-fluorophenol. The peak at 6000 cm^‑1 was assigned to H tunneling. Nevertheless, the 13000 cm^-1 feature remains unassigned. In this work, we performed a theoretical analysis, investigating two hypotheses for explaining the 13000 cm^‑1 signal. The first hypothesis is that it is due to one-photon absorption followed by ionization through resonant multiphoton dissociation. The second hypothesis is that the signal is due to two-photon absorption into a superexcited state, which dissociates yielding an H atom. We discuss the pros and cons of each hypothesis, laying the groundwork for future experiments.