Uracil-adenine dimer connected by an excess electron

In this work we consider a new form of the uracil-adenine dimer anion (AU^-) where the two monomers are connected by an excess electron suspended between them. An equilibrium structures of the anion was predicted using uncorrelated and correlated ab initio quantum-mechanical calculations. An AU^- anion of this kind can be formed in the gas phase by an attachment of an adenine molecule to a dipole-bound electron of uracil. Removal of the excess electron from the anion and optimization of the geometry of the neutral cluster starting from the geometry of the anion initially leads to a significant increase of the separation between the bases, but eventually the optimization converges to an H-bonded structure very dissimilar from the anion structure.