Electron-Induced Fragmentation Dynamics of 1-Methylpyrene (C ₁₇ H ₁₂ ) Dications and Trications: C ₂ H _<i>x</i> ^{<i>q</i> +} Release Pathways

The dissociation behavior of 1-methylpyrene (MP) was investigated by using the SWEET experimental system under electron-induced collisions to elucidate the fragmentation dynamics of polycyclic aromatic hydrocarbon (PAH) ions. Molecular interaction with 200 eV electrons initiated multiple ionization and fragmentation pathways, resulting in molecular cation production. The unfragmented monocation MP⁺ is identified as the most abundant one, the intact dication MP²⁺, the de-ethylated dication, and a stable trication MP³⁺ were also observed, demonstrating the formation and stability (>ms) of highly charged molecular ions. Among the smaller observed hydrocarbon fragments, neutral C₂H_<i>x</i>⁰ and cationic C₂H_<i>x</i>⁺ species were the predominant dissociation products. Experimental findings were compared with density functional theory-based tight-binding molecular dynamics simulations. Measurements of the cation signals as a function of the incident electron energy (17-35 eV) provided appearance energies for the dications and correlated cations. The higher experimental appearance energy values relative to simulated vertical ionization energies suggest the involvement of autoionization processes from initially populated electronically exited states of the molecule.