Nonreactive Scattering of N₂from Layered Graphene Using Molecular Beam Experiments and Molecular Dynamics

Abstract

Conventional gas surface interaction (GSI) models and molecular dynamics (MD) simulations have been compared with angular distributions and average translational energies for N2 scattered from highly oriented pyrolytic graphite (HOPG) measured by angle and velocity resolved molecular beam scattering experiments. The translational energy and angular distributions of the scattered N2 were obtained for incidence energies near 30 and 68 kJ mol–1, incidence angles of 30°, 45°, and 70°, and a surface temperature of 677 K. The trajectories of scattered nitrogen molecules were found to fall into three main categories, i.e., single collision, multiple collisions with escape, and multiple collisions without escape. While the conventional GSI models did not match the translational energy and angular distributions obtained from the experiments, the results obtained from MD simulations were found to be in good agreement. The MD simulations also showed that the number of surface layers used to model the HOPG surface and the carbon–nitrogen Lennard-Jones potential are important in improving the agreement between the simulations and the experiments.

A review of gas-surface interaction models for orbital aerodynamics applications

“…The characteristics mentioned above are well described by the cube models [117] reviewed in the previous section of this paper, because of the inherent assumptions on which these models are built. Better agreement, as expected, is found with the SC [89,105,106] rather than with the HC model [108,112,113,116,117,121], not only because of the more realistic gas-surface interaction potential assumed, but also because adjustments can be made through the parameter W for the system considered. When the attractive well W dominates the dynamics, the repulsive potential assumption loses accuracy and the HC model fails in describing trapping and partial accommodation to the surface.…”

“…While Maxwell's model fails in reproducing the petal-shaped angular distribution observed in these experiments, it appears that its theoretical apparatus and simplified assumptions are sufficient to describe some re-emission polar plots showing a small nearly specular and a large diffuse component [104,107]. Results provided by Mehta et al [108] show that when the CLL model is adopted some difficulties are encountered in the attempt of selecting the proper combination of α n and σ t to reproduce the experimental conditions. Excellent predictions of the position of the peak (θ r,max ) and of the dispersion of the scattering distribution, for selected values of the accommodation coefficients, seem to exclude an accurate representation of the experimental E r /E i , and viceversa.…”

“…When this condition is observed, the re-emission distribution is said to be superspecular. The effect seems to be more noticeable for nearly grazing angles of incidence [108]. With regards to translational energy distributions, when the conservation of the tangential momentum is observed, the relative ratio between the mean final and incident energies varies according to the parallel momentum conservation curve:…”

“…As the incident kinetic energy of the beam increases (within the limits of the thermal scattering domain), the effect of surface thermal vibration on the angular scattering distribution becomes less dominant. As a consequence, the lobal distribution becomes narrower and more symmetrical in shape, the scattered intensity at the peak increases [113] and θ r,max generally moves towards the tangent to the surface [108,112,119,120] (Figure 10, top right). When this condition is observed, the re-emission distribution is said to be superspecular.…”

Analysis of Three-Dimensional Protein Structure of CBAVD in Indonesia as a Basis for Immunotherapy to Ensure Maternal Health

“…The tertiary structure of a protein is a protein structure on top of a secondary structure consisting of irregular bonds between R groups of various amino acids. The tertiary structure of a protein is a threedimensional conformation that focuses on the bonds between secondary structures 14 . The three-dimensional structural modeling of proteins consists of the homology/comparative method, the fold recognition method and the ab initio method 15 .…”