Interaction ofH2and He with metal atoms, clusters, and ions

The binding energy, equilibrium geometry, and electronic structure of molecular hydrogen and helium atoms interacting with Ni, Cu, Co, and Al atoms and cations have been calculated using self-consistent-field linear combination of the atomic-orbitals–molecular-orbital method. The exchange interaction between the electrons is treated using the unrestricted Hartree-Fock theory. Correlation is included using Möller-Plesset perturbation theory up to the fourth order. The accuracy of the calculation is tested by comparing the results of the ground-state spin and binding energy with available experiments on dimers. While a neutral metal atom is found to dissociate the ${\mathrm{H}}_2$ molecule, the metal cations bind the ${\mathrm{H}}_2$ molecule associatively and with rather large binding energy. The binding of the He atom to a metal cation is found to be analogous to that of a ${\mathrm{H}}_2$ molecule since both possess closed electronic shells. The number of hydrogen molecules and He atoms that can be bound to a metal cation at a given temperature and gas density is studied using the effective-medium approximation and density-functional theory. The results are compared with recent experiments.