Exothermic dissociation

Detailed analysis of the Oad positions following dissociation at room temperature shows that most Oad are found one lattice constant (in the [0 0 1] direction) away from the Ob-vac that is filled, the rest being immediately adjacent and two lattice constants away [50]. As there is little thermal diffusion of Oad on Ti02(l 1 0), the separation of Oad from the closest positions to the reacting Ob-vacs was attributed to the energy released during the exothermic dissociation of 02 (calculated at 3.5 eV [18]) in a similar way to that observed, for example, for Cl2 dissociation on Ti02(l 1 0) [51],... 

Liquid anhydrous ammonia in contact with the eyes may cause serious injury to the cornea and deeper structures and sometimes blindness on the skin it causes first- and second-degree burns that are often severe and, if extensive, may be fatal. Vapor concentrations of 10,000 ppm are mildly irritating to the moist skin, whereas 3 0,000 ppm or greater causes a stinging sensation and may produce skin burns and vesiculation. With skin and mucous membrane contact, burns are of three types cryogenic (from the liquid ammonia), thermal (from the exothermic dissociation of ammonium hydroxide), and chemical (alkaline). ... 

Through exothermic dissociation of a neutral excited state in molecule by electron transfer to an adjacent molecule. This process leads to the generation of geminately bound electron-hole pairs as precursors of free positive and negative charges in an organic solar cell. 

Tetrahedral N4 is expected to dissociate into two N2 molecules, but this reaction is forbidden by orbital symmetry. Dunn and Morokuma [33] characterized a transition state for the exothermic dissociation of tetrahedral N4 into two N2 and estimated the activation barrier to be 63 kcal/mol at the CASSCF(12e,12o) level, which indicates that N4 is a metastable species with significant kinetic stability. The calculated potential energy surface of N4 suggests that the low-lying triplet state might cross with the singlet surface (Fig. 3), which could reduce the activation energy barrier to about 30 kcal/mol [29,31,32],... 

With the exception of gas-phase exothermic dissociations, our choice of Dab in polyatomic molecules is uniquely defined. Because the overwhelming majority of dissociation processes are endothermic (and this is exactly the reason why catalysts are often required to make these processes happen), they are within the scope of our modeling. 

The He22+, 022+ and NF2+ diatomic dications have ground state energy curves that are characterized by a short equilibrium bond distance, an exothermic dissociation energy and a barrier to dissociation that bestows kinetic metastability on the dication. Due to their finite lifetimes all three dications have been detected experimentally. 

For HeC ", Hartree-Fock SCF calculations were reported for the X I" ground state by Harrison et al. [91] and by Cooper and Wilson [83] who also calculated HeN and HeO ", The potential energy curves of the low-lying electronic states of HeC [8] and NeC [9] were calculated by Koch et al. using a complete active space SCF (CASSCF) approach. From these calculations it is predicted that the (X X ) ground state of HeC is thermodynamically stable with D = 16.6 kcal/mol [8] while NeC " (X X ) has a barrier for the exothermic dissociation into Ne ( P)- -C ( P) of 37.3 kcal/mol. 

Barnes and Tomlinson (68) used DTA to analyze a mixture for silver carbonate in the presence of silver(II) oxide. The method, as based on the DTA curve in Figure 7.28, is applicable quantitatively for mixtures containing more than 20% Ag2C03 and semiquantitatively for 5%. The first curve peak is caused by the exothermic dissociation of AgO, or... 

In order to see the threshold behaviour of such a reaction and its marked contrast with the exothermic dissociative charge transfer, the cross-section curves for the two reactions... 

Fig. 22. Comparison of values and energy dependence of cross-sections for endothermic dissociative charge transfer with those for exothermic dissociative charge transfer. (From ref. 180.)...

Materials such as propellants and explosives contain tightly bonded groups of atoms which retain their molecular character until a sufficient stimulus is applied to cause exothermic dissociation. This, in turn, triggers further dissociation leading to initiation or ignition. The macroscopic behavior or equation of state is ultimately controlled by microscopic properties such as the interatomic forces. Only when it is possible to quantitatively describe these forces will it be possible to predict whether a given molecular structure will support an explosive reaction. It is toward advances in this area relative to metal azides that this chapter is devoted. 

The growth mechanism appears to be the same irrespective of type of hydrocarbon and whether it is the endothermic dissociation of methane or the exothermic dissociation of carbon monoxide (8). However, the resulting morphology and degree of graphitization depends on parameters such as type of hydrocarbon, metal, particle size, and temperature. Hence, there might not be a unique growth mechanism for the formation of carbon fibers and nanotubes. 

A deprotonation energy of 48.1 kcal/mol and an activation barrier of 42.8 kcal/mol were calculated with a Cl method for the strongly exothermic dissociation reaction PH + PH+ + H+ [6, 7]. 

For dissociation reactions in which the reverse, recombination step is slow, dissociation is virtually complete once the pair has separated to the contact distance. Under these conditions the magnitude of the interaction in the dissociated pair, in particular the screening of this interaction by ions, would not affect the dissociation rate. In terms of the Hammond postulate [22] and its extensions [23] an exothermic dissociation process would have its transition state close to the bound state, so that the equilibrium and recombination rate coefficients would change in parallel. In such a case one expects no salt effect on the dissociation reaction, in agreement with the classical picture of Bronsted and Bjerrum for kinetic salt effects [7]. 

According to HOMO-LUMO considerations, addition of H2 to Pd2 is clearly symmetry-allowed. As a result, exothermic dissociation of H2 on Pd2 becomes possible, whereas on an isolated Pd atom the dissociation reaction does not occur. 

Fig. 2b is a compound Morse potential for simulating the exothermic dissociation of a hypothetical diatomic molecular crystal of A2 A2 = A+A+energy. A form of this potential was used in problem (3) for studying the profile of a detonation wave. In this potential ... 

Exothermic Dissociation of A2 Energy Exchange in Rapid Reactions... 

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