An excess electron suspended between two polar molecules. Ab initio study of uracil · H₂O and uracil · HF anions

Metastable anions of uracil complexes with water and hydrogen fluoride where the excess electron is suspended between the two monomers have been investigated using ab initio calculations. Anions of this class can be formed by attachment of a polar molecule to a dipole-bound excess electron of the uracil anion. This provides a bonding effect sufficient to stabilize the dimer in a local minimum of the potential energy surface. Removal of the excess electron leads to a significant change of the structure of the complex which rearranges and forms a conventional hydrogen-bonded dimer.