The mechanism of decomposition of Angeli's salt, Na2N2O3, was explored with B3LYP and CBS-QB3 computational methods. Angeli's salt produces both nitroxyl (HNO) and nitric oxide (NO), depending upon the pH of the solution. These calculations show that protonation on N(2), while less favorable than O protonation, leads spontaneously to HNO production, while cliprotonation at O(3) leads to NO generation. K-a values for protonation at different centers and rate constants have been found which reproduce experimental data satisfactorily.