Stereodynamics in dissociative adsorption of NO on Si(111)

Pathways of NO adsorption on Si(100)2×1 by van der Waals corrected DFT

In the current study, the NO adsorption on the Si(100) surface was investigated by DFT including van der Waals forces (vdW). Stable molecular and dissociative configurations were found and compared to previous studies. Furthermore, additional states were investigated where NO adsorbs across dimers. The transformation of NO from molecular adsorbate into a dissociated adsorbate migrated into the subsurface was investigated by nudged elastic band. Several pathways were explored, either multi-staged, or direct from molecular into subsurface migrated configurations, both including and excluding vdW forces. The energy barriers of the single steps of multi-staged pathways never exceed 0.15[Formula: see text]eV and are, in general, smaller when NO is adsorbed across dimers rather than bridged on a single dimer and when including vdW. Furthermore, the oxygen-bridged configurations are kinetically more accessible than the nitrogen-bridged ones.

A new perspective: imaging the stereochemistry of molecular collisions

The concept of the steric effect plays a central role in chemistry. This Perspective describes how the polarization of reactant molecules in space can be used to probe directly the steric effect, and highlights some of the new measurements that are made possible by coupling reactant orientation and alignment with ion imaging techniques.

Coupling scanning tunneling microscope and supersonic molecular beams: a unique tool for in situ investigation of the morphology of activated systems

We report here on a new experimental apparatus combining a commercial low temperature scanning tunneling microscope with a supersonic molecular beam. This setup provides a unique tool for the in situ investigation of the topography of activated adsorption systems and opens thus new interesting perspectives. It has been tested towards the formation of the O/Ag(110) added rows reconstruction and of their hydroxylation, comparing data recorded upon O(2) exposure at thermal and hyperthermal energies.

PRODUCT ROTATIONAL ANGULAR MOMENTUM POLARIZATION IN REACTIONS D + FCl(v = 0,j = 0) → DCl + F, DF + Cl

A comparative quasi-classical trajectory study on the product alignment and orientation of reactions D + FCl (v,j) → DCl + F , DF + Cl are carried out on a recently computed 12A′ ground-state surface reported by Deskevich et al. The reaction probabilities, integral and differential cross-sections as a function of collision energy are presented. The differential cross-sections and 〈P2(j′ ⋅ k)〉 are governed by different reaction mechanisms for these two reactions. P(θr) and P(ϕr) distributions of products DCl and DF at four selected collision energies of 5, 10, 16 and 30 kcal/mol indicate that DCl and DF product molecules are not only aligned, but also oriented along y-axis. By comparing the P(θr) and P(ϕr) distributions of reactions H + FCl (v = 0,j = 0) → HCl + F and H + FCl (v = 0,j = 0) → HF + Cl , mass factor has some influence on stereodynamics of the title reactions, but the features of PES should have major influence on the difference between dynamics of reactions D + FCl (v = 0,j = 0) → DCl + F and D + FCl (v = 0,j = 0) → DF + Cl .

Product rotational angular momentum polarization in the H+FCl(v=0-5, j=0, 3, 6, 9)→HF+Cl reaction

The product alignment and orientation of the title reaction on the ground potential energy surface of 1 (2)A' have been studied using the quasi-classical trajectory method. The calculations were carried out for case (a) at collision energies of 0.5-20 kcal mol(-1) with the initially rovibrational state of the reagent FCl molecule being at the v = 0 and j = 0 level to especially reveal in detail the dependence of the product integral cross section on collision energy. Further calculations at the collision energy of 15 kcal mol(-1) for case (b) at v = 0-5, and j = 0, and (c) at v = 0, and j = 3, 6, 9 initial states were carried out to reveal the effect of initially vibrational and rotational excitations on stereodynamics, respectively. Possessing final relative velocity k' (defined as a vector in the xz-plane), product alignment perpendicular to the reagent relative velocity vector k (defined as z- or parallel to the z-axis), for case (a) is found to be weaker at all collision energies, for case (b) is found to be vibrationally enhanced by the reactant molecule FCl, but for case (c), rather insensitive to initially rotational excitation. The rotational vector of product molecular orientation pointing to either negative or positive direction of the y-axis in the center of mass frame, e.g. origin of the coordinate system, is enhanced by collision energies regarding to 0.5-20 kcal mol(-1), while it becomes weaker at higher vibrational (v = 0-5) or rotational (j = 0, 3, 6, 9) excitation levels. Effects of collision energies and of rotational excitation at these collision energies, with 15 kcal mol(-1) as an example on the calculated PDDCSs are also shown and discussed. Detailed plots P(φ(r)) in the range of 0 ≤φ(r)≤ 360(o), and P(θ(r), φ(r)) in the ranges of 0 ≤θ(r)≤ 180° and 0 ≤φ(r)≤ 360° at collision energies 0.5-20 kcal mol(-1) have been presented. Overall, results of PDDCSs of the product alignment and product orientation at these collision energies in the title reaction are not very strongly distinguishable.

Surface chemical reactions induced by well-controlled molecular beams: translational energy and molecular orientation control

I review our recent studies of chemical reactions on single-crystalline Cu and Si surfaces induced by hyperthermal oxygen molecular beams and by oriented molecular beams, respectively. Studies of oxide formation on Cu induced by hyperthermal molecular beams suggest that the translational energy of the incident molecules plays a significant role. The use of hyperthermal molecular beams enables us to open up new chemical reaction paths, and to develop new methods for the fabrication of thin films. Oriented molecular beams also demonstrate the possibility for controlling surface chemical reactions by varying the orientation of the incident molecules. The steric effects found on Si surfaces hint at new ways of achieving material fabrication on Si surfaces. Controlling the initial conditions of incoming molecules is a powerful tool for creating new materials on surfaces with well-controlled chemical reactions.