Total energy calculations were performed for nitrous oxide and its anion N2O- by Multi Configuration Self-Consistent Field-Configuration Interaction (MCSCF-CI) methods. The shape of the lowest unoccupied molecular orbital (LUMO) and the energy gap between the highest occupied molecular orbital (HOMO) are evaluated for different N-2-O distances and bending angles. The vertical electron affinities for the ground state and the first excited bending mode were found to be -2.1 eV, separated by about 50 meV. On the (2)A' potential energy surface (PES) of negatively charged N2O the dynamics for the reaction after charge transfer on the ground state and thermally excited N2O has been studied by wave packet calculations. The molecules dissociate within 30 fs and strong rotational excitation of the N-2 fragment is found. To explain the strong vibrational state selectivity we propose diabatic transitions between the (2)A' and the (2)A" PES to interrupt the dissociation of N2O- selectively. Implications for the dynamics of the Eley-Rideal reaction of N2O on alkali metal surfaces are discussed in connection with exoemission experiments.