Temperature dependence of the dissociative sticking probability of N2 on Fe(111): evidence for both a direct and a precursor mechanism Original Research Article

The dissociative sticking probability of N2 molecules hitting a perfect Fe(111) surface with an impact energy of 1.05 eV has been simulated by classical molecular dynamics as a function of crystal temperature. The results are in qualitative agreement with experimental molecular beam results, where it is found that the dissociation probability decreases with increasing crystal temperature. Analysis of the simulations showed that three mechanisms, a direct, an intermediate and a precursor mechanism contribute to the dissociation probability in the temperature range of 100–500 K. For the direct mechanism, dissociation upon impact, the dissociation probability increases with increasing crystal temperature. For the intermediate mechanism, dissociation after direct impact but before thermal equilibration with the crystal, the dissociation probability decreases with increasing crystal temperature. For the precursor mechanism, the temperature dependence is found to be the same as for the intermediate mechanism. The observed dissociation probability is a sum of these contributions and dominated by the contributions from the latter two mechanisms. Consequently, the dissociation probability is a sum of contributions from different mechanisms with opposite temperature dependencies, rather than the result of a single mechanism.