A kinetics and mechanistic study of the atmospherically relevant reaction between molecular chlorine and dimethyl sulfide (DMS)

A gas-phase kinetics study of the atmospherically important reaction between Cl2 and dimethyl sulfide (DMS)Cl2 + CH3SCH3 → products has been made using a flow-tube interfaced to a photoelectron spectrometer. The rate constant for this reaction has been measured at 1.6 and 3.0 torr at T = (294 ± 2) K as (3.4 ± 0.7) × 10–14 cm3 molecule–1 s–1. Reaction (1) has been found to proceed via an intermediate, (CH3)2SCl2, to give CH3SCH2Cl and HCl as the products. The mechanism of this reaction and the structure of the intermediate were investigated using electronic structure calculations. A comparison of the mechanisms of the reactions between Cl atoms and DMS, and Cl2 and DMS has been made and the relevance of the results to atmospheric chemistry is discussed

Some spectroscopic studies related to atmospheric chemistry and the thermal decomposition of organic azides

The work described in this thesis is a study of the thermal decomposition of some aliphatic azides and of the atmospherically relevant reaction between dimethyl sulphide (DMS) and molecular chlorine.  The aim of the work was to describe the mechanisms with which these reactions take place, and to identify the most important parameters influencing the reactions, such as decomposition temperature or reaction time. UV-photoelectron spectroscopy (PES) and infrared matrix isolation spectroscopy have been used to monitor the extent of the reaction and to detect intermediates and products, and ab initio calculations have been used to facilitate spectral assignments and to provide information on the electronic structure and the thermochemistry of the reactions studied.   In the DMS + Cl2 reaction, evidence of formation of an unstable (CH3)2SCl2 species was found;  for the first time structural and spectroscopic information have been described for this reaction intermediate. The pyrolysis of ten aliphatic azides has been studied:  two general modes of thermal decomposition were observed which were interpreted in terms of two types of reaction mechanism.  In some cases the reaction involved formation of reaction intermediates:  two of them have been observed and characterized for the first time.</p

Some spectroscopic studies related to atmospheric chemistry and the thermal decomposition of organic azides

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Water adsorption on diamond (111) surfaces: an ab initio study

The physical and chemical adsorption of water at the (1 Ã 1) and (2 Ã 1)-reconstructed C(111) surfaces are investigated by means of first principles calculations and compared to hydrogen adsorption. The study aims at filling a gap of knowledge about the interaction of water with the most stable diamond surface. The calculated reaction energies and barriers indicate that the Pandey-reconstructed surface is almost inert towards water and hydrogen chemisorption in comparison with the unreconstructed surface and other low-index diamond surfaces. We also show that by increasing the amount of chemisorbed hydroxyl or hydrogen groups the stability of the Pandey reconstruction is progressively reduced with respect to the unreconstructed (111) surface, which becomes energetically more favourable above about 40% of adsorbate coverage. Our results provide a microscopic description of diamond surface passivation, which is very important for controlling macroscale phenomena, such as the friction reduction of diamond coatings in humid environments

Grafting Crown Ether Alkali Host-Guest Complexes at Surfaces by Electrospray Ion Beam Deposition

The functionalization of surfaces with host guest compounds is promising for many applications, yet often limited by constraints such as the volatility of the functional compound or the lack of binding to the surface. We use electrospray ion beam deposition (ES-MD) on surfaces in ultrahigh vacuum as a novel approach to modify an atomically defined copper surface with preformed dibenzo-24-crown-8-alkali complexes, in which the central ion (H+, Na+, or Cs+) can be exchanged in the electrospray solution. In situ scanning tunneling microscopy maps the single alkali ion complexes as an oval protrusion with a four-lobe submolecular structure immobilized at the surface. Density functional theory calculations confirm that the crown ether is bound to the surface via the central alkali ion within its cavity, indicating that the properties of the molecular complex are retained after deposition

Portrait of the potential barrier at metal-organic nanocontacts

Electron transport through metal-molecule contacts greatly affects the operation and performance of electronic devices based on organic semiconductors(1-4) and is at the heart of molecular electronics exploiting single-molecule junctions(5-8). Much of our understanding of the charge injection and extraction processes in these systems relies on our knowledge of the potential barrier at the contact. Despite significant experimental and theoretical advances a clear rationale of the contact barrier at the single-molecule level is still missing. Here, we use scanning tunnelling microscopy to probe directly the nanocontact between a single molecule and a metal electrode in unprecedented detail. Our experiments show a significant variation on the submolecular scale. The local barrier modulation across an isolated 4-[trans-2-(pyrid-4-yl-vinyl)] benzoic acid molecule bound to a copper(111) electrode exceeds 1 eV. The giant modulation reflects the interaction between specific molecular groups and the metal and illustrates the critical processes determining the interface potential. Guided by our results, we introduce a new scheme to locally manipulate the potential barrier of the molecular nanocontacts with atomic precision

Portrait of the potential barrier at metal-organic nanocontacts

Resumen del trabajo presentado al Symposium on Surface Science (3S), celebrado en St. Christoph am Arlberg (Austria) del 7 al 13 de marzo de 2010

Ideal adhesive and shear strengths of solid interfaces: A high throughput ab initio approach

We release a computational protocol to calculate two intrinsic tribological properties of solid interfaces from first principles, namely the adhesion energy, γ and the ideal interfacial shear strength, τ. These properties, which correspond to the energy required to separate two surfaces from contact and to the static friction force per unit area, respectively, are ruled by physical/chemical interactions between the surfaces in contact. First principles calculations based on Density Functional Theory (DFT) can accurately describe surface-surface interactions, offering the possibility to characterize the adhesive and shear strengths of materials in silico. We implemented the computational protocol as an AiiDA workflow (WF) that allows to obtain the γ and τ figures of merits in a high throughput manner. The software we produced uses a simple input file and most computational parameters determined automatically. To our best knowledge, this is the first time a high throughput approach has been used in tribology