Dynamics of the vibrational mode-specific proton transfer reaction NH3+(ν1) + NH3 → NH2 + NH4+: ab initio MO and classical trajectory studies Original Research Article

The effects of collision energy and vibrational excitation of a NH stretching mode (ν1) of NH3+ on the title reaction have been studied by means of both ab initio MO and quasi-classical trajectory calculations. The potential energy surface (PES) of the proton transfer reaction calculated showed that an intermediate complex (NH4+ · NH2) is formed at the exit region on the PES. By using the analytical function fitted to the ab initio PES, the trajectory calculations were performed under the pseudo-three-particle approximation at the range of collision energy of 0.98–25.0 kcal/mol. The reaction cross section calculated gradually decreases with collision energy. The trajectory calculations with the vibrational excited NH3+ (ν1 = 1) ion suggested that the ν1 excitation causes a slight lowering of the reaction cross section at low-collision energy below 1 eV, whereas at higher energy the effect of ν1 excitation is negligibly small. The decrease due to the ν1 mode excitation was less than that of the collision energy. The present theoretical result is in good agreement with a recent experiment by Zare and co-workers. The reaction mechanism was discussed on the basis of the theoretical results.