Structures and C-H bond energies of hydrogenated polycyclic aromatic hydrocarbons

Density functional calculations are employed to calculate C-H bond dissociation energies of sp(3) centers at different locations of a variety of polycyclic aromatic hydrocarbons (PAHs). The computed bond dissociation energies D-e range from less than 80 kJ mol(-1) for a hydrogen atom bound to the basal plane of a PAH layer up to 300 kJ mol(-1) for a CH-H bond on a zigzag border position. Besides this not unexpected dependence on the specific process, we observe a pronounced scatter of dissociation energies with the size and shape of PAHs, which reflects the complex chemistry for graphitic carbon reactions. On the basis of the present treatment, we determine reasonable estimates for the hydrogenation energies of extended graphite sheets, which have been considered as important in the modeling of carbon deposition by pyrolysis of light hydrocarbons.