Ab initio study of the effects of orientation and corrugation for H2 adsorbed on polycyclic aromatic hydrocarbons

This paper reports state-of-the-art ab initio calculations at the second order of Moller-Plesset perturbation theory of molecular hydrogen interaction with polycyclic aromatic hydrocarbons (PAHs) up to coronene (C24H12). The effects of both H-2 orientation with respect to the PAH plane and of PAH corrugation have been carefully investigated. It was found that the energetic preference for the perpendicular H-2 orientation over the parallel one decreases rapidly as the PAH grows. The detailed study of coronene-H-2 potential energy surface has made it possible to estimate from first principles the graphite-H-2 binding energy. This ab initio estimate is shown to be in fair agreement with experiment. As revealed by the example of benzene-H-2 dimer, the electrostatic energy component plays an important role in PAH-H-2 interactions, that stems largely from the charge penetration effect and, therefore, cannot be reproduced by the simple quadrupole-quadrupole interaction model.