Atom mechanics

The mechanism of the synthesis reaction remains unclear. Both a molecular mechanism and an atomic mechanism have been proposed. Strong support has been gathered for the atomic mechanism through measurements of adsorbed nitrogen atom concentrations on the surface of model working catalysts where dissociative N2 chemisorption is the rate-determining step (17). The likely mechanism, where (ad) indicates surface-adsorbed species, is as follows ... 

This analysis makes possible the determination of a chemical diffusion coefficient from experimental data having made no use of a model, and which takes no account of tire atomic mechanism of diffusion, and assumes tlrat the same chemical diffusion coefficient applies to each component of the alloy. 

Y. Yano and S. Oae, 3d Orbital Resonance in the Bivalent Sulfur Atom, Mechanisms of Reactions of Sulfur Compounds, Vol. 4, Intra-Science, 1969, p. 167. 

However, as the CH3 + O reaction shows [67], the roaming atom mechanism is not limited to closed-shell adducts, nor is it limited to abstraction pathways that are barrierless (see Fig. 13). Finally, the photodissociation of CH3CHO implies that the roaming fragment may not be limited to H atoms [55]. It remains to be seen how universal roaming mechanisms are, but they have the potential to be competing pathways in a large number of reactions. 

In mechanism (8.43) the bridgehead hydrogens of barrelene should be found at the a positions of semibullvalene (2a, 0/3,0y). Mechanism (8.44) can give three different hydrogen-label distributions. If the final bond formation is concerted with bond fission, and bond fission and formation take place at the same carbon atom [mechanism (8.44A)], the label distribution should be (la, 0/3, ly). If bond formation is concerted with bond fission but with a preference for bond formation at the carbon allylic to bond fission [mechanism (8.44B)], the label distribution should be (2a, 0/3, Oy). If there is a symmetric allylic biradical which has a finite existence [mechanism (8.44AB)], then the hydrogen-label distribution should be (1.5a, 0/3,0.5y). 

According to the Oxford English Dictionary, the word molecule seems to have arisen in the seventeenth century in the discussions initiated by the physical speculations of Descartes. Early formal definitions described a molecule as a group of atoms mechanically indivisible (H. E. Roscoe, Elementary Chemistry [1871], p. 169) or a group of atoms drawn and held together by what chemists call affinity (J. Tyndall, Longm. Mag. 1 [1882], 30). 

Around 400 K there is a phase transition to a disordered but still cubic structure associated with the terminal oxygen atom in a WO4 tetrahedron which can migrate to another tetrahedron, thereby reversing the direction in which a pair of tetrahedra point. Nevertheless the same general atomic mechanisms are responsible for the negative thermal expansion up to the decomposition temperature. 

Atomization of melts has been used in two principal areas, i.e., powder production 4] and spray forming, 3] as shown in Figs. 1.4 and 1.5, respectively. It is not until recent years that the technologies for the atomization of melts have advanced sufficiently to ensure good yields of usable products over sustained periods of plant operation. In these two areas, some aspects such as melting of metals or alloys, basic atomizer designs, and atomization mechanisms are the same or similar. Metals or alloys melt at high temperatures to produce low viscosity but usually... 

Scale-up of gas atomizers is difficult and it requires the use of higher gas-to-melt mass flow rate ratio to maintain the same droplet size. The scale-up may also cause some complex phenomena to occur, such as the disappearance of the prefilming effect in close-coupled atomizers, the generation of turbulence in melt flow within delivery nozzle, and change in atomization mechanisms. 

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