  To investigate the gas-phase hydrogenation processes of large, astronomically
relevant cationic polycyclic aromatic hydrocarbon (PAH) molecules under the
interstellar environments, the ion-molecule collision reaction between six PAH
cations and H-atoms is studied. The experimental results show that the
hydrogenated PAH cations are efficiently formed, and no even-odd hydrogenated
mass patterns are observed in the hydrogenation processes. The structure of
newly formed hydrogenated PAH cations and the bonding energy for the
hydrogenation reaction pathways are investigated with quantum theoretical
calculations. The exothermic energy for each reaction pathway is relatively
high, and the competition between hydrogenation and dehydrogenation is
confirmed. From the theoretical calculation, the bonding ability plays an
important role in the gas-phase hydrogenation processes. The factors that
affect the hydrogenation chemical reactivity are discussed, including the
effect of carbon skeleton structure, the side-edged structure, the molecular
size, the five- and six-membered C-ring structure, the bay region structure,
and the neighboring hydrogenation. The IR spectra of hydrogenated PAH cations
are also calculated. These results we obtain once again validate the complexity
of hydrogenated PAH molecules, and provide the direction for the simulations
and observations under the coevolution interstellar chemistry network. We infer
that if we do not consider other chemical evolution processes (e.g.,
photo-evolution), then the hydrogenation states and forms of PAH compounds are
intricate and complex in the interstellar medium (ISM).
