Diatomic molecules reactions

V.B). Experimental distributions obtained for the Ne+-N2 system (Fig. 54) were shown to be intermediate between those predicted by application of the Franck-Condon principle and those predicted by such a statistical model. Finally, it has been suggested by Tomcho and Haugh411 that the molecular orbitals of the transient triatomic system should be considered in predicting vibrational distributions of products from atomic-ion-diatomic-molecule reactions. Calculations based on this approach are in progress for the (Ar-N2)+ system.417... 

Calculations of potential surfaces are now in progress for a number of triatomic systems of atmospheric importance.488, 489 These have direct pertinence to various atomic-ion-diatomic-molecule reactions. 

Atom + Diatomic Molecule Reactions studied by Reactive Scattering [358]... 

Class IV . The first reactant is at a three-fold hollow site and the second is at a next nearest neighbour bridge site. Indeed, this represents a very common structure for a transition state on a (111) metal surface. Transition states with this structure are often observed in the dissociation of diatomic molecules - reactions which are the reverse of those currently under discussion. DFT calculations have shown that the dissociation of N2, CO, and on a variety of transition metal surfaces all proceed via this... 

For the more general case of a non-linear collision of an H-atom with an H2-molecule, classical trajectory calculations were first made by WALL et al./53/ and KARPLUS et al /54/ Similar calculations have been performed more recently for a number of atom-diatomic molecule reactions /55-57/. 

State-of-the-art classical dynamics calculations combined with ab initio methods are illustrated by a recent study of the bimolecular, atom-diatomic molecule reactions involving H, N, and O. These reactions are important in the oxidation of nitrogen and in the combustion of nitrogen-containing fuels. Global potential energy surfaces for the A, A", and A" HNO states have been formulated and used in a classical trajectory study of the reactions ... 

A lot of the impetus for current applications of classical trajectories in studies of atom-diatomic molecule reactions is the desire to understand the elementary reactions that occur in the atmosphere. This is the motivation for some recent studies of the reaction of ground-state nitrogen atoms with NO ... 

Table 2 List of Selected Classical Trajectory Studies of Atom-Diatomic Molecule Reactions...

R. E. Wyatt, Quantum mechanics of neutral atom-diatomic molecule reactions, in State to State Chemistry , P. R. Brooks and E. F. Hayes, eds., ACS Symposium Series, No. 56,... 

The semiempirical methods deal with three-particle collinear activated complexes, and so they can really describe only atom -h diatomic molecule reactions. The basic ideas can still be used for more complicated cases, however, by considering the three central atoms with the semiempirical formulas and adding structural and vibration frequency information from other sources (see Smith and Zellner, 1974 Ernst et al, 1977, 1978 Zahniser et al, 1978). 

The direct dissociation of diatomic molecules is the most well studied process in gas-surface dynamics, the one for which the combination of surface science and molecular beam teclmiques allied to the computation of total energies and detailed and painstaking solution of the molecular dynamics has been most successful. The result is a substantial body of knowledge concerning the importance of the various degrees of freedom (e.g. molecular rotation) to the reaction dynamics, the details of which are contained in a number of review articles [2, 36, 37, 38, 39, 40 and 41]. 

The reaction of an atom with a diatomic molecule is the prototype of a chemical reaction. As the dynamics of a number of atom-diatom reactions are being understood in detail, attention is now being turned to the study of the dynamics of reactions involving larger molecules. The reaction of Cl atoms with small aliphatic hydrocarbons is an example of the type of polyatomic reactions which are now being studied [M, 72, 73]. 

Chain reactions such as those described above, in which atomic species or radicals play a rate-determining part in a series of sequential reactions, are nearly always present in processes for the preparation of thin films by die decomposition of gaseous molecules. This may be achieved by thermal dissociation, by radiation decomposition (photochemical decomposition), or by electron bombardment, either by beams of elecuons or in plasmas. The molecules involved cover a wide range from simple diatomic molecules which dissociate to atoms, to organometallic species with complex dissociation patterns. The... 

Valence bond diagrams, for SN2 reactions, 60 Valence bond (VB) model for diatomic molecules, 15-22 empirical (EVB), 58-59 EVB mapping potential, 87, 88... 

FIGURE 9.13 Le Chatelier s principle predicts that, when a reaction at equilibrium is compressed, the number of molecules in the gas phase will tend to decrease. This diagram illustrates the effect of compression and expansion on the dissociation equilibrium ot a diatomic molecule. Note the increase in the relative concentration of diatomic molecules as the system is compressed and the decrease when the system expands. 

The following flasks show the dissociation of a diatomic molecule, X2, over time, (a) Which flask represents the point in time at which the reaction has reached equilibrium ... 

The halogens include fluorine, chlorine, bromine and iodine and all have been used in CVD reactions. They are reactive elements and exist as diatomic molecules, i.e., F2, CI2, etc. Their relevant properties are listed in Table 3.2. 

Role of Atomic Hydrogen. The stable hydrogen diatomic molecule (H2) dissociates at high temperature (>2000°C) or in a high current-density arc to form atomic hydrogen. The dissociation reaction is highly endothermic (AH = 434.1 KJmofi). 

Other reactions have extremely small equilibrium constants. For example, elemental fluorine, a diatomic molecule under standard conditions, is nevertheless at equilibrium with fluorine atoms ... 

If we move the chemisorbed molecule closer to the surface, it will feel a strong repulsion and the energy rises. However, if the molecule can respond by changing its electron structure in the interaction with the surface, it may dissociate into two chemisorbed atoms. Again the potential is much more complicated than drawn in Fig. 6.34, since it depends very much on the orientation of the molecule with respect to the atoms in the surface. For a diatomic molecule, we expect the molecule in the transition state for dissociation to bind parallel to the surface. The barriers between the physisorption, associative and dissociative chemisorption are activation barriers for the reaction from gas phase molecule to dissociated atoms and all subsequent reactions. It is important to be able to determine and predict the behavior of these barriers since they have a key impact on if and how and at what rate the reaction proceeds. 

Figure 1. Qne-dinenslonal Lennard-Jcnes potential energy diagram for adsorption of a diatomic molecule (liydrogen). p denotes liie reaction coordinate.

For both reactions studied, NO+CO and NO+propene, the effect of electrochemically pumped Na in increasing the extent of NO dissociation is large and significant. This is because unpromoted low index planes of Pt, Pt(lll), are relatively inert towards NO dissociation and we adscribe the NO dissociation as the key reaction-initiating step. Such dissociation of diatomic molecules in the field of coadsorbed cations has been discussed in detail by Lang et al [29], The rates of production of CO2. N2 and NjO all depend on... 

The first step in interstellar chemistry is the production of diatomic molecules, notably molecular hydrogen. Observations of atomic hydrogen in dense clouds show that this species cannot be detected except in a diffuse halo surrounding the cloud, so that an efficient conversion of H into H2 is necessary. In the gas phase this might be accomplished by the radiative association reaction,... 

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