This paper presents classical dynamics simulations of Si(CD3)3+scattering from a hexanethiolate self-assembled monolayer on Au(111) and from a clean Au(111) surface. Simulations are performed with a united atom model using purely repulsive scattering potentials. These simulations predict the partitioning of the incident ion kinetic energy into the scattered ion kinetic energy and the internal modes of both the surface and the ion. For the organic surface, the simulations predict energy transfer to surface, ion internal, and ion kinetic energies of 0.78, 0.11, and 0.12 of the collision energy. The corresponding transfer efficiencies of 0.12, 0.21, and 0.65 were calculated for the Au(111) surface. These computational results compare well with the experimental results on the same systems which are reported in the preceding paper. The simulations predict near specular scattering for both surfaces. They also demonstrate that the ion penetrates only the topmost two to three layers of Me atoms of the organic surface and that it spends up to 250 fs in contact with the surface. Finally, these calculations determine the dependence of energy transfer on the incident ion angle.

The quantitative kinetic model presented in this work provides insights of the inner mechanisms that play a key role in the natural oxidative degradation (photoinduced and thermal) of a model polymer, polyethylene oxide (PEO). A set of key reactions is selected from ab initio data, theoretical rate constant calculations, and experimental rate constants. Experimental results, i.e., induction times and quantities of carbonyl end-products, are accurately reproduced by this model. While this study grasps the complexity of the degradation mechanism, results depend mainly on the reactivity of peroxy radicals and that of hydroperoxide groups. Three pathways are available to the peroxy species, i.e., intermolecular and γ-intramolecular H-abstraction reactions, and the termination reaction. The competition between these processes is the driving force of the degradation mechanism. Moreover, in thermo-oxidative conditions, the relative quantities of esters and formates depend strongly on four competitive hydroperoxide decomposition channels, i.e., the unimolecular, bimolecular, induced decomposition by hydroxyl radicals and the hydroperoxide H-abstraction reaction. Many of the reactions investigated here participate also in polymer synthesis, pyrolysis or other degradation processes. Moreover, the simple structure of the model polymer in this work is representative of a wide range of polymer systems.

International audienceUsing a model analytic potential energy function for Aln clusters [J. Chem. Phys. 1987, 87, 2205] and a UMP2(fc)/6-31G* potential derived here for the Ar---Al interaction, classical trajectory simulations are performed to study collision-induced dissociation (CID) of Al6 and Al13 with Argon. For the octahedral Al6 (Oh) cluster, the CID threshold is ~14 kcal/mol higher than the true threshold. This is because, near the threshold, there are no trajectories which transfer all the reactant relative translational energy to Al6 internal energy. For the planar Al6 (C2h) cluster, the CID threshold is closer to the true threshold. For the spherically shaped Al6 (Oh) and Al13 (D3d) clusters, T->V is the predominant energy transfer pathway. T->R energy transfer is important for the planar Al6 (C2h), Al13 (D2h), and Al13 (D6h) clusters. T->V energy transfer is enhanced as the cluster is softened (i.e., its vibrational frequencies lowered), the mass of the colliding atom is increased, and/or the relative velocity is increased. These effects are consistent with a previously derived impulsive model [J. Chem. Phys. 1970, 52, 5221], which says T->V energy transfer increases as the collisional adiabaticity parameter x is decreased