Competition between Loss of H2 versus H+H in the Fragmentation of the Fluorene Cation

Abstract

The fluorene cation is a frequently studied molecule in the context of fragmentation experiments. This is because of its potential role in interstellar chemistry, notably as a precursor of PAH cages. In this paper, we analyze H, H⁺ , H₂ and $H_2^{+}$ losses from the fluorene cation using the SMF (Statistical Molecular Fragmentation) model. We calculate the probabilities of all the 534 possible fragmentation channels as a function of the excitation energy, up to the loss of three hydrogens. Four different types of hydrogen atom pairings (from the same carbon, from the same ring, from different rings and across-the-bay) have been tested in order to determine which types contribute to the actual production of hydrogen molecules. The simulated breakdown curves are in very good agreement with different experimental results when same ring pairing is taken into account. It was possible to deduce from the model the locations of the emitted H, H⁺ , H₂ and $H_2^{+}$ species.

Keywords: Density Functional Theory; Fluorene; Fragmentation; Molecular Hydrogen; Statistical Molecular Fragmentation.