Dispersion and polar flattening: noble gas-halogen complexes.

High-level ab initio calculations on the complexes between noble gas atoms (He, Ne, Ar, Kr, and Xe) and dihalogen molecules (F2, Cl2, Br2, and I2) reveal trends, both in interaction energies and the energy difference between the linear and T-shaped structures, that can be explained well in terms of dispersion interactions enhanced by polar flattening of the halogens. The partial discrepancies with experimental findings are discussed. Graphical abstract The molecular electrostatic potential (red positive, blue negative) of Cl2...Br2 projected onto the 0.003 a.u. isodensity surface.