Ab initio theoretical study of dipole-bound anions of molecular complexes (HF)(n)/^-, n = 5-9

Ab initio calculations have been performed to determine structures and electron detachment energies of the hydrogen fluoride hydrogen-bonded polymers, (HF)(n)/^-, n = 5-9. In these systems, the excess electron is bound by virtue of the dipole-electron interaction. It was found that, unlike the neutral complexes which form cyclic structures, the equilibrium geometries of the anions have 'zig-zag' linear shapes. For all the five complexes, the predicted vertical detachment energies are positive (307, 363, 405, 437, and 461 meV for (HF)₅/^-, (HF)₆/^-, (HF)₇/^-, (HF)₈/^-, and (HF)₉/^-, respectively). These results were obtained at the Moller-Plesset second-order level of theory at the geometries of the anions calculated at the Hartree- Fock level. The calculations also indicate that up to n = 8, the (HF)(n)/^- anions are metastable systems with respect to electron detachment and simultaneous transformation of the cluster to the most stable cyclic configurations. However, calculations predict that starting from (HF)₉/^- the linear HF cluster anions are adiabatically stable systems.