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

Intermolecular interactions between the simple amines NH3, CH3NH2, (CH3)(2)NH, and (CH3)(3)N and the F-2 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-F-2 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 F-2 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 F-2. The F-2 distance in these complexes is widened by 0.3-0.4 Angstrom relative to the isolated F-2 molecule, and the N ... F distance shrinks from 2.6 Angstrom in ammonia-F-2 to 1.84 Angstrom in methylamine-F-2 and remains approximately at that value in the other two complexes. (C) 1999 Elsevier Science B.V. All rights reserved.