Theoretical study of M(+)-RG2 (M+ = Li, Na, Be, Mg; RG = He-Rn).

Ab initio calculations were employed to determine the geometry (MP2 level), and dissociation energies [MP2 and RCCSD(T) levels], of the MIIa+–RG2 species, where MIIa is a group 2 metal, Be or Mg, and RG is a rare gas (He–Rn). We compare the results with similar calculations on MIa+–RG2, where MIa is a group 1 metal, Li or Na. It is found that the complexes involving the group 1 metals are linear (or quasilinear), whereas those involving the group 2 metals are bent. We discuss these results in terms of hybridization and the various interactions in these species. Trends in binding energies, De, bond lengths, and bond angles are discussed. We compare the energy required for the removal of a single RG atom from M+–RG2 (De2) with that of the dissociation energy of M+–RG (De1); some complexes have De2 > De1, some have De2 < De1, and some have values that are about the same. We also present relaxed angular cuts through a selection of potential energy surfaces. The trends observed in the geometries and binding en...