Theoretical study of adsorption and dissociation of NH3 on pentanuclear Fe(111) surface

Theoretical study regarding the adsorption and dissociation of NH3 molecule on Fe(111) surface has been carried out. The method used was DFT-B3LYP, and the basis sets used were ECP and 6-311G**. This research aimed at giving the theoretical understanding of adsorption and dissociation of NH3 molecule on Fe(111) surface. The adsorption and dissociation were studied based on the energetic parameter, bond length, electron population, vibration and orbital interaction. The result of theoretical calculation revealed that the on top position is the interaction position with the minimum energy for the adsorption of NH3 molecule on Fe(111) surface. The analysis of electron population of the two composing molecular orbitals indicated that the transfer of electron has an important role in the mechanism of adsorption. The visualization of molecular orbital showed that the transfer of electron occurred in the electron pairs of the interacting orbital. Relating to the adsorption mechanism and the overlapping of interaction orbitals, NH3 molecule provides the Highest Occupied Molecular Orbital (HOMO) as the interaction pair for the Lowest Unoccupied Molecular Orbital (LUMO) on Fe surface. The insignificant difference between the oxidation state of N and H atoms as well as the higher hemolytic N-H bond dissociation energy (compared to heterolytic dissociation) cause the adsorption mechanism of NH3 on Fe(111) model to occur through homolytic-dissociative chemisorption.