RESUMEN

The adsorption of nitrogen molecules on a (100) tungsten surface has been studied using a new potential energy surface in which long-range interactions are suitably characterized and represented by the Improved Lennard-Jones function. The new potential energy surface is used to carry out molecular dynamics simulations by adopting a semiclassical collisional method that explicitly includes the interaction with the surface phonons. The results of the sticking probability, evaluated as a function of the collision energy, are in good agreement with those obtained in the experiments and improve the already good comparison recently obtained with calculations performed using interactions from the Density Functional Theory method and corrected for long-range van der Waals contributions. The dependence of trapping probability on the surface temperature for a well-defined collision energy has also been investigated.

RESUMEN

The inelastic scattering of N2 molecules from silica surfaces, taken at 100 K, has been investigated by adopting a semiclassical collision model in conjunction with the appropriate treatment of the long-range interaction forces. Such forces promote the formation of the precursor state that controls all basic elementary processes occurring at the gas-surface interphase. The probabilities for the different elementary surface processes triggered by quartz are determined and compared with those recently obtained for another silica polymorph (cristobalite). In addition, the final roto-vibrational distributions of N2 molecules undergoing inelastic scattering have been characterized. N2 molecules, impinging on both considered surfaces in low-medium vibrational states, preserve the initial vibrational state, while those inelastically scattered are rotationally excited and translationally colder. The surface temperature effect, investigated by raising the temperature itself from 100 K up to 1000 K, emerges more sharply for the cristobalite polymorph, mainly for the molecules impinging in the ground roto-vibrational state and with low collision energies.

Asunto(s)

Dióxido de Silicio , Vibración , Temperatura , Probabilidad

RESUMEN

The O/ß-quartz interaction is described by combining our time-dependent semiclassical approach to atom-molecule/surface scattering with first-principles electronic structure calculations at the DFT (PBE0) level of accuracy. In particular, the O, O(2) interaction potentials with an on-top Si atom and its nearest O atom both localized over three different silica clusters have been calculated as a function of the oxygen-silica approaching distance. The calculated DFT potential energy surface has been used in semiclassical trajectory calculations to investigate the sticking and inelastic reflection of oxygen atoms from a model ß-quartz surface. The collisional mechanism, including the role played by the phonon dynamics, is brought to light and accurate sticking probabilities are calculated at five impact energies in the range [0.05-0.8] eV and T(S) = 1000 K. The different catalytic response of ß-quartz and ß-cristobobalite to the atomic oxygen flux is also discussed and highlighted.