Using ab initio direct dynamics, selected reaction trajectories were calculated for the title reaction, The lifetime of the intermediate ion-molecule complex formed upon encounter of the reactants depends strongly on their initial relative orientation. When the proton to be transferred is properly lined up between the oxygen and the nitrogen, rapid transfer is observed. This leads to deposition of a high and nonstatistical fraction of the reaction enthalpy into the product ammonium ion. Less favorable initial orientations appear to give a more statistical distribution of the energy. A strong basis set dependence of the dynamics is observed. It is concluded that moderately large basis functions including polarization functions should be used for future dynamical studies. Alternatively, precise analytical surfaces may be used.