An application of the Reaction Class Transition State Theory/Linear Energy Relationship (RC-TST/LER) is presented for the evaluation of the thermal rate constants of hydrogen abstraction reactions by H atoms from Polycyclic Aromatic Hydrocarbons (PAH). Two classes of reactions have been considered, namely hydrogen bonded to six- and five-membered rings, respectively, and twenty-two reactions have been used to develop the RC-TST/LER parameters. B3LYP and BH&HLYP density functional theory methods were used to calculate necessary potential energy surface information. Detailed analyses of RC-TST/LER reaction factors lead to the conclusion that rate constants for any reaction in these two classes can be approximated by those of its corresponding principal reaction corrected by the reaction symmetry factor. Specifically, for hydrogen abstraction from six-membered rings such as naphthalene and pyrene, k(T) = (/H+C_6H_6) kH+C_6H_6 = (/6){1.42 × 108T1.77 exp(-6570/T)}(cm~3/mol·s), and for hydrogen abstraction from five-membered rings such as acenaphthylene and acephenanthrylene, k(T) = (/H+C_(12)H_8) kH+C_(12)H_8 = (/2){3.27 × 108T1.71 exp(-8170/T)} (cm~3/mol·s), where σ is the reaction symmetry number.
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