QUANTUM-CHEMICAL STUDY OF THE REACTION OF AMMONIA WITH TRANSIENT OXYGEN SPECIES

Quantum-chemical calculations of reaction pathways between ammonia and transient oxygen atomic and molecular species have been carried out. Access of atomic oxygen is the easiest from the direction of the base of the ammonia pyramid, neutral oxygen being inserted into the N-H bond to form NH2OH moiety whereas in the case of atomic ion O- ammonia tends to topple over at the reaction coordinate of 1.8 angstrom to form an ONH3- complex. Also if the approach of O2- molecular ion starts from the direction of the hydrogen base of ammonia pyramid then at 1.6 angstrom the ammonia molecule topples over to form a pi-complex of oxygen with nitrogen, next the O-O bond splits with large energy expense and finally HNO- ion is formed. However, when the assumed influence of the surface is modelled e.g. by prohibiting ammonia toppling over (atomic attack) or by activation of the dioxygen (molecular attack), the energy barriers are substantially reduced and the hydrogenolysis reaction takes place. The geometry of the surface reaction and the activation of molecules play thus the crucial role in the choice of the reaction pathway by the reacting system.