This review describes five categories of the reactions of polycyclic aromatic
hydrocarbons, including photochemistry, electron attachment/detachment, recombination
processes, radical reactions, and ion-neutral chemistry. For each class of reaction, an
overview of the studies and their general results are presented, as well as references to
the literature. The thermochemistry of PAHs and relevant species is described, including
bond dissociation energies, ionization energies, electron affinities, basicities,
acidities, and the interrelationships of these quantities. Modeling of the chemistry of
PAHs and their ions is discussed for both diffuse and dark clouds. The role of PAH cations
in the catalytic formation of molecular hydrogen is considered. Finally, this review
concludes with a discussion of current challenges in the chemical characterization of
PAHs, and a perspective for future studies.