Ab initio study of proton transfer in ammonium nitrate dimer

Abstract

Proton transfer (PT) in ammonia-nitric acid system is studied by ab initio calculations in this work. PT does not occur in global-minimum structure of a single ammonium nitrate unit (monomer). The compulsory occurrence of PT in the monomer causes the formation of large dipole moment, whereas the total energy is destabilized. However, with the extent of intensive external electric field, PT spontaneously occurs in the monomer and moreover the total energy becomes lower than that of the global-minimum structure due to the dipole-electric field interaction energy. In two ammonium nitrate units (dimer), PT does occur to enhance internal dipole moments. On the basis of these results, it is revealed that the dipole-dipole interaction between the monomers in dimer not only promotes the occurrence of PT but also contributes to stabilize the total energy of the system.