Chemical reactions atom transfer

Let us now turn to the influence of vibrations on exchange chemical reactions, like transfer of hydrogen between two O atoms in fig. 2. The potential is symmetric and, depending on the coupling symmetry, there are two possible types of contour plot, schematically drawn in fig. 17a, b. The O atoms participate in different intra- and intermolecular vibrations. Those normal skeleton... 

Cryochemical research in the past 15 years has established the existence of the low-temperature limit of rate constants of various solid-state chemical reactions with transfer of atoms and molecular fragments of different masses over distances comparable with intermolecular ones, from H-atoms transfer under intramolecular rearrangement to organic radicals and halogen atom... 

Atomic and Molecular Collisions Coherent Control of Chemical Reactions Energy Transfer, Intramolecular Ion Kinetics and Energetics Kinetics, Chemical Molecular Beam Epitaxy, Semiconductors... 

In all chemical reactions, the reacting atoms or molecules pass through a state that is intermediate in structure between the reactant(s) and the product(s). Consider the transfer of a proton from a water molecule to a chloride anion ... 

Chemical reactions, which involve direct charge transfer between the metal atom in the lattice of the metal and the oxidising species. 

Because electrons can be neither lost nor created in a chemical reaction, all the electrons lost by the species being oxidized must be transferred to the species being reduced. Because electrons are charged, the total charge of the reactants must be the same as the total charge of the products. Therefore, when balancing the chemical equation for a redox reaction, we have to balance the charges as well as the atoms. 

Chemical vapor deposition may be defined as the deposition of a solid on a heated surface from a chemical reaction in the vapor phase. It belongs to the class of vapor-transfer processes which is atomistic in nature, that is the deposition species are atoms or molecules or a combination ofthese. Beside CVD, they include various physical-vapor-deposition processes (PVD) such as evaporation, sputtering, molecular-beam epitaxy, and ion plating. 

The molybdenum and tunsten diphenylacetylene compounds have been chemically useful primarily as precursors to the quadruple metal-metal bonded dimers [M(Por)]2, formed by solid-state vacuum pyrolysis reactions. However. Mo(TTP)()/"-PhC CPh) is also a useful substrate in atom-transfer reactions, reacting with Sx or Cp2TiS i to form Mo(TTP)=S. The reaction can be reversed by treatment of Mo(TTP)=S with PPh (which removes sulfur as PhxP=S) and PhC CPh. The order of preference for ligand binding to molybdenum 11) has been established to be PPh < PhC CPh < 4-picoline. ... 

One of the most fundamental chemical reactions is the combination of a hydroxide ion (OH ) and a hydronium ion (H3 0+) to produce two molecules of water OH" (a g) + H3 (a g) 2 H2 O (/) A molecular view of this reaction (Figure 4-7f shows that the hydroxide anion accepts one hydrogen atom from the hydronium cation. Taking account of charges, it is a hydrogen cation (H ) that is transferred. The reaction occurs rapidly when H3 O and OH ions collide. The hydroxide anion accepts a hydrogen cation from the hydronium cation, forming two neutral water molecules. 

For a better understanding of the effect of changing concentrations on the rate of a chemical reaction, it helps to visualize the reaction at the molecular level. In this one-step bimolecular reaction, a collision between molecules that are in the proper orientation leads to the transfer of an oxygen atom from O3 to NO. As with the formation of N2 O4, the rate of this bimolecular reaction is proportional to the number of collisions between O3 and NO. The more such collisions there are, the faster the reaction occurs. 

To determine whether electrons are transferred in chemical reactions, chemists use a procedure that assigns an oxidation number (also known as an oxidation state) to each atom in each chemical species. In a redox reaction, electron transfer causes some of the atoms to change their oxidation numbers. Thus, we can identify redox reactions by noting changes in oxidation numbers. 

In the past it had been a popular belief that the electrochemical reduction of any inorganic or organic substance involves the primary electrochemical formation of a special, active form of hydrogen in the nascent state (in statu nascendi) and subsequent chemical reaction of this hydrogen with the substrate. However, for many reduction reactions a mechanism of direct electron transfer from the electrode to the substrate could be demonstrated. It is only in individual cases involving electrodes with superior hydrogen adsorption that the mechanism above with an intermediate formation of adsorbed atomic hydrogen is possible. 

The numbers in the parentheses indicate the phases in which the reactants and the products are soluble. Since X does not dissolve in phase 2 and Y in phase 1, their only possible meeting place is the interface between the two phases, 1 and 2. It is necessary to transport atoms of X and of Y to the interface. The reaction product XY has also to be transported away from the interface. The reaction would otherwise come to a halt due to the accumulation of XY at the interface. Each of these individual processes mentioned may be addressed as kinetic steps and for the reaction cited, these steps are (a) the transfer of X from the bulk of phase 1 to the interface (b) the transfer of Y from the bulk of phase 2 to the interface (c) chemical reaction at the interface and (d) the transfer of XY from the interface into the bulk of phase 1 (say). The steps listed can be grouped into two categories. The steps (a), (b), and (d) are mass transfer processes, while the step (c) is a chemical reaction step. A simpler situation is encountered in many of the reactions in process metallurgy. Phase 1 is a gas... 

The effects of transfer of atoms by tunneling may play an essential role in a number of phenomena involving the transfer of atoms and atomic groups in the condensed phase. One may expect that these effects may exist not only in the proton transfer reactions considered above but also in such processes as the diffusion of hydrogen atoms and other light ions (e.g., Li+) in liquids, tunnel inversion and isomerization in some molecules, quantum diffusion of defects and light atoms in the electrode at cathodic incorporation of the ions, ion transfer across the liquid/solid interface, and low-temperature chemical reactions. 

Chemiluminescence is defined as the production of light by chemical reactions. This light is cold , which means that it is not caused by vibrations of atoms and/or molecules involved in the reaction but by direct transformation of chemical into electronic energy. For earlier discussions of this problem, see 7 9h Recent approaches towards a general theory of chemiluminescence are based on the relatively simple electron-transfer reactions occurring in aromatic radical-ion chemiluminescence reactions 10> and on considerations of molecular orbital symmetry as applied to 1.2-dioxetane derivatives, which very probably play a key role in a large number of organic chemiluminescence reactions 11>. 

Chemical reaction rates, 14 607. See also Kinetic measurements Chemical reactions. See also Chemical processes Reaction entries with absorption, 2 47-48, 71-76 activated carbon for control of, 4 755 on adsorbents, 2 629-630, 650-651 atomic level of, 16 736 contexts of, 22 336 engine knock and, 22 390—391 heterogeneous, 22 331-332, 339 homogeneous, 22 339 independent and dependent, 22 336—337 mass-transfer coefficients with, 20 753-755... 

---