Photodissociation of methyl nitrite on Ag(111): Simulation

Abstract

The photodissociation dynamics of methyl nitrite, CH 3 ONO, on Ag͑111͒ have been simulated using a description that models 61 cis-methyl nitrite molecules adsorbed on a three-layer block of Ag͑111͒. Based on classical intra-and intermolecular potentials and periodic boundary conditions, molecular dynamics ͑MD͒ simulation led to two domain structures at 100 K: those with CONO planes oriented nearly parallel and nearly perpendicular to the Ag͑111͒ surface. To simulate photodissociation dynamics of NO, many NO trajectories were determined, each carried out as follows. At some instant of the MD simulation, a CH 3 ONO molecule was randomly selected from within the group of 61 and its internal CH 3 O-NO bond was stretched to a defined dissociation transition state. The nascent NO was given momentum along the direction of the bond broken and NO translational and internal energies were chosen to match those determined experimentally in collision-free gas phase photodissociation. The motion of the whole adsorbate-substrate system was then calculated while following the trajectory of NO. Analyzing the ensemble of NO trajectories, we conclude that, while the initial orientation of the dissociating CH 3 ONO influences the number of subsequent collisions, the exit direction, and the final translational and internal energy of NO, it does not fully account for the properties of ejected NO. Furthermore, for those molecules lying nearly parallel to the surface, a transition state prepared by simply stretching the ON bond is often located away from the lowest potential energy exit path due to interactions with nearest neighbor species. As a result, coordinates, e.g., internal twisting, other than the internal CH 3 O-NO stretching mode are intimately involved in the dissociation channel.

Photodissociation at 193 nm of tert-Butyl Nitrite on Ag(111)

“…According to the proposed model, preparation of a saturated monolayer of TBN will form the most stable configuration since the as-dosed layer is thermally treated at 140 K. This should lead to a single layer with minimal local randomness and no long-range roughness. Consistent with this and an experimental report 22 and theoretical calculations, , the collisionless NO (Figure ) exhibits a strong angular dependence favoring, by a factor of 7, ejection at 40° compared to 0°. The intermediate component follows a similar profile but increases by a factor of 3, indicating partial memory of its initial direction even after at one weak collision with the surroundings.…”