N atoms recombination on a silica surface: A global theoretical approach

The paper reports on a semiclassical dynamics study about N-2 formation after nitrogen atom recombination on a silica surface via the Eley-Rideal collisional mechanism at T = 1000 K. The molecular dynamics study was carried out using a fitted potential energy surface based on new density functional computations on clusters cleaved from the beta-cristobalite unit cell. The B3LYP results obtained using silica clusters of increasing dimensions (up to Si7O14H14) show that only atomic nitrogen is adsorbed (binding energy E-b congruent to 2.7-2.8 eV). Then, the obtained potential energy surface has been used in a time-dependent semiclassical collisional method which is able to describe, at a very detailed level, the recombination of N atoms on the surface assisted by the phonon excitation mechanism of the substrate. The recombination coefficient gamma of the Eley-Rideal recombination mechanism was calculated together with the reaction energetics. (c) 2006 Elsevier B.V. All rights reserved.