We have used transition state theory to derive analytical expressions for the rates of desorption of atoms and molecules (diatomic as well as polyatomic) from solid surfaces. Realistic forms for the three dimensional adsorbate-surface interaction potentials are employed, including surface corrugation. Using potential parameters from a combination of experiment and ab initio calculations we have applied the rate expressions to evaluate the temperature programmed desorption spectra of NH3 from Ni(111). Comparing these curves to the experimental spectra leads to a bond energy of D0=21.0–3.7Θ kcal/mol, where Θ is the fraction of saturation coverage.
The molecular mechanics (MM) and density functional theory (DFT) methods were used to study the role of hair structure on the adsorption of various explosive molecules (TATP, TNT, NG, EGDN, and RDX). The present study is limited to adsorption of explosives onto the hairs outer surface while possible diffusion into deeper layers in the hair is neglected. The adsorption properties of the hair surface are estimated from changes in the Gibbs free energy. The calculations suggest that the molecular adsorption of all explosives examined is due mainly to interaction between the molecule and the lipid layer that covers the hair surface. The binding of explosive molecules to the lipid layer consists of interplay between dispersive and Coulomb interactions as well as the distortion of the lipid layer induced by the molecular adsorption. The relative importance of these effects depends on the chemical nature, the size, and the shape of the adsorbed molecule. Several possible adsorption positions, along the lipid molecules, were found for all adsorbates examined. The theoretical prediction that explosive molecules adsorption is mainly due to the interaction with the lipid layer was examined and partially proved experimentally. Moreover, comparison of the calculated results with available experimental data allowed us to obtain the temperature-dependent sticking probability of the various explosives to the hair surface.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDynamics of surface-aligned photochemistry (Theory). IV. Hydrogen atom reactions in the hydrogen bromide(ad)/lithium fluoride(001) + h.nu. systemV. J. Barclay, D. B. Jack, J. C. Polanyi, and Y. ZeiriCite this: J. Phys. Chem. 1993, 97, 48, 12541–12552Publication Date (Print):December 1, 1993Publication History Published online1 May 2002Published inissue 1 December 1993https://pubs.acs.org/doi/10.1021/j100150a016https://doi.org/10.1021/j100150a016research-articleACS PublicationsRequest reuse permissionsArticle Views29Altmetric-Citations14LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts
Classical molecular dynamics simulations have been performed to study the details of collision-induced desorption (CID) of nitrogen molecules adsorbed at low coverages on Ru(001). Semiempirical potential energy surfaces (PES) were used to describe the movable two layers of 56 ruthenium metal atoms each, the nitrogen adsorbate, the Ar and Kr colliders, and the interactions between them. An experimentally measured threshold energy for the CID process of 0.5 eV and the dependence of the cross section σdes on incidence energy and angle of incidence have been precisely reproduced in the energy range of 0.5–2.5 eV. Strong enhancement of the σdes is predicted as the angle of incidence increases. Kinetic energy and angular distributions of the scattered rare gas and the desorbing nitrogen were determined as a function of the dynamical variables of the collider. It is predicted that half of the collision energy is transferred to the solid and the other half is shared among the two scattered species. While no vibrational excitation is observed, efficient rotational energy excitation is predicted which depends on both incident energy and angle of incidence. Polar and azimuthal angular distributions were found to be strongly dependent on the incidence angle and energy of the colliders. These results suggest a new CID mechanism for the weakly chemisorbed nitrogen molecules on Ru(001), based on extensive analysis of individual trajectories. According to this mechanism, the CID event is driven by an impact excitation of frustrated rotation or tilt motion of the adsorbed molecule as a result of collision with the energetic rare gas atom. In addition, lateral motion along the surface is also excited. Strong coupling of these two modes with the motion in the direction normal and away from the surface eventually leads to desorption and completes the CID process. The efficiency of this coupling is dictated by the details of the corrugation of the Ru–N2 PES. It is concluded that the simple hard cube–hard sphere model, frequently used to analyze CID processes, is insufficient for the description of this system. While reasonably well predicting threshold energy, it cannot explain the full dynamical picture of the CID event.
Electronic excitation in a semiconductor induced by the collision of energetic atoms with the solid surface is investigated theoretically. The modeling has been performed for a one-dimensional independent-electron system where the solid is described by a chain of 10–20 atoms. The time evolution of the nuclei (i.e., colliding atom and chain atoms) has been described by classical mechanics while quantum mechanical description has been used for the electronic dynamics. The two systems (i.e., the atoms and the electron) were coupled to each other and the equations of motion were solved self-consistently. Energy dissipation from the chain to the rest of the solid was included via the GLE approach. This study establishes the relationship between the probability of electron–hole formation and various parameters of the system such as collider translational energy, magnitude of the band gap, and existence of impurities in the solid. In addition, two excitation mechanisms were examined, electronic excitation due to a direct coupling between the electron and the colliding atom and an indirect mechanism due to electron–phonon coupling.
