Molecular beam studies of the dynamics of activated adsorption of N2 on W(110): Dissociation threshold and new binding states
Abstract
The activated adsorption of N2 on W(110) was studied using molecular beams to achieve translational energies from 2 to 30 kcal/gmol. The beams were formed in nozzles with and without helium seeding. For the lowest beam kinetic energy the probability of dissociation upon collision was about 3 × 10-3, increasing to 3 × 10-1 at energies above 20 kcal/gmol. The dependence of the dissociation probability on nitrogen coverage suggested the process was direct in nature, not trapping dominated. The results show that the adsorption is translationally activated and that the reactive collision is not adequately described by a single one-dimensional barrier. As the beam energy was increased, the apparent saturation coverage by nitrogen increased, producing an unusual desorption state above a nitrogen atom coverage of 0.25. Nitrogen desorbed autocatalytically from this state in a fashion observed previously for high concentration of oxygen from Pt(100). The emergence of this state at higher surface coverages indicates that the state of nitrogen adsorbed on tungsten and other metals at higher pressures may be quite different from the state normally observed in low pressure studies. © 1984.