Nonadditive effects in ternary H2-cation-PAH systems

This article reports state-of-the-art ab initio calculations at the second order of Møller-Plesset perturbation theory of molecular hydrogen binding in its ternary complexes with lightweight alkali cations (M = Li or Na) and polycyclic aromatic hydrocarbons (PAHs) up to coronene. The study revealed a substantial nonadditive contribution to the H(2) stabilization energy. In the most stable conformation, the nonadditive contribution weakens the H(2) binding by a factor of nearly 1.5 and 1.3 for Li and Na cations, respectively, as compared with the pairwise sum of direct H(2)-M(+) and H(2)-PAH contributions. In the Li case, the presence of PAH not only does not promote H(2) binding but has a large (approximately 20%) weakening effect in comparison with the initial H(2)-Li(+) interaction. In the Na case, the presence of PAH has the usual stabilizing influence on the hydrogen binding. A careful analysis of the physical components of the nonadditive effect on the example of H(2)-M(+)-benzene complexes revealed the dominating role of the induction nonadditivity.