Computational study on the negative electron affinities of NO2-•(H2O)n clusters (n=0-30)

Here we report negative electron affinities of NO2-center dot(H2O)(n) clusters (n=0-30) obtained from density functional theory calculations and a simple correction to Koopmans' theorem. The method relies on the calculation of the detachment energy of the monoanion and its highest occupied molecular orbital and lowest unoccupied molecular orbital energies, and explicit calculations on the dianion itself are avoided. A good agreement with resonances in the cross section for neutral production in electron scattering experiments is found for n=0, 1, and 2. We find several isomeric structures of NO2-center dot(H2O)(2) of similar energy that elucidate the interplay between water-water and ion-water interactions. The topology is predicted to influence the electron affinity by 0.5 and 0.4 eV for NO2-center dot(H2O) and NO2-center dot(H2O)(2), respectively. The electron affinity of larger clusters is shown to follow a (n+delta)(-1/3) dependence, where delta=3 represents the number of water molecules that in volume, could replace NO2-. (c) 2007 American Institute of Physics.