The structure of eight-carbon monolayers on the H-terminated Si(111) surface was investigated by a molecular simulation method. Molecular mechanics calculations showed that the best substitution percentages on the Si(111) surface were 50% for octene or octyne-derived monolayers and 40% for the styrene or phenylacetylene-derived monolayers. These values are in good agreement with the experimental results. After a two-dimensional cell containing alkyl chains and four layers of Si atoms was constructed, the densely packed and well-ordered monolayer on the Si(111) surface can be shown at the molecular level. At the same time, the thickness of the monolayers and the tilt angle of the alkyl chain were also calculated. Additionally, the theoretical calculations showed that the C=C bond of the alkyne only reacts once with the H-terminated Si(111) surface, that is only one Si-C bond per organic molecule is formed on the Si(111) surface, which verifies the experimental results. It is thus shown that molecular simulation can provide otherwise inaccessible microscopic information at the molecular level, and may be considered as a useful adjunct to experiments.

A new quantum mechanical study on UV photodissociation of H2O2 at 248 and 266 nm using a 2D fit to the Schinke-Staemmler's (SS) potential energy surface (PES) [Chem. Phys. Lett. 145, 486 (1988)] is reported. The rotational distributions of the product OH on both the A and B surfaces are found to be considerably hotter than those obtained in a previous quantum study [J. Chem. Phys. 98, 6276 (1993)] using an empirical PES with a very weak dependence on the torsional angle. The new calculation shows that the rotation distributions in both the A and B states are Gaussianlike with a maximum at j=8 on the A surface and at j=9 on the B surface at 248 nm. Similar distributions are found at 266 nm, but with the maximum shifting lower by approximately one quanta in both the A and B states. The dissociation preferentially produces OH rotations with a high j1～j2 correlation. These conclusions are in excellent agreement with the classical calculation of Schinke-Staemmler at 193 nm photolysis. Although the j distribution (rotation of OH) is similar on both surfaces, the j12(j12=j1+J2) distribution, which reflects the vector correlation of j1 and j2, is quite different on two surfaces. Our calculation shows that the A surface gives rise to more bending excitation than the B surface, reflected by a hotter j12 distribution on the A surface. The A and B state branching ratio of H2O2 is also evaluated at 248 and 266 nm photolysis.

The ONIOM quantum mechanics method is used in this article to study one-carbon unit transfer from an imidazolidine to 6-aminouracil derivates. The computation results show that this reaction can be completed via three paths, owing to the three different proton transfer modes. Each path experiences three processes of nucleophile attacking, proton transferring, and bond rupturing. The focus of discussion falls on the proton transfer process. By analyzing the calculation results, we find that the direct proton transfer is the preferable pathway.

A simple model, i.e., sodium bis(2-ethylhexyl) sulfosuccinate (AOT) represented by one-head and two-tail beads tied together by a harmonic spring and water or iso-octane by one bead, was put forward via dissipative particles dynamics (DPD) simulation method. Using the changes of interfacial tension between water and oil phase, a ternary phase diagramof AOT/water/iso-octane system was drawn.