The intermolecular interaction between amines and F2. An ab initio study

Intermolecular interactions between the simple amines NH3, CH3NH2, (CH3)2NH, and (CH3)3N and the F2 molecule were investigated by ab initio SCF and MP2 methods, and with a density functional theory approach. In agreement with rotational spectroscopic data, the ammonia–F2 complex behaves like a weakly bound intermolecular complex with modest intramolecular relaxation of the constituent monomers. Upon successive methyl substitution the interaction energy between the amine and F2 increases systematically and these complexes should be described as charge transfer complexes with essential contributions originating from intramolecular structure relaxations in the amine and in F2. The F2 distance in these complexes is widened by 0.3–0.4 Å relative to the isolated F2 molecule, and the N⋯F distance shrinks from 2.6 Å in ammonia–F2 to 1.84 Å in methylamine–F2 and remains approximately at that value in the other two complexes.