Electronic structure calculations of acetonitrile cluster anions: Stabilization mechanism of molecular radical anions by solvation

Systematic electronic structure calculations have been performed for (CH3CN)n-(n=2-10) anion clusters with the hybrid B3LYP and non-hybrid PW91 density-functional methods in order to understand the stabilization mechanism of an acetonitrile dimer radical anion core by solvent molecules. Since the excess negative charge is mainly localized on N atoms in the dimer anion core, solvent acetonitrile molecules are bound to the N atoms by C-H⋯Nδ− hydrogen-bond-like attractive interaction with the binding energy per bond being about 10-13 kcal/mol. Due to this stabilization mechanism, the anion cluster for n ⩾ 4-6 is stable with respect to the electron autodetachment. Geometry optimization was also carried out for the (CH3CN)6- anion cluster where an excess electron was internally trapped. The size dependence of the stabilization energy and vertical detachment energy for the (CH3CN)n- anion clusters is discussed.