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 (C(24)H(12)). 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.