Molecular decomposition

The rates of these reactions bodr in the gas phase and on the condensed phase are usually increased as the temperature of die process is increased, but a substantially greater effect on the rate cati often be achieved when the reactants are adsorbed on die surface of a solid, or if intense beams of radiation of suitable wavelength and particles, such as electrons and gaseous ions with sufficient kinetic energies, can be used to bring about molecular decomposition. It follows drat the development of lasers and plasmas has considerably increased die scope and utility of drese thermochemical processes. These topics will be considered in the later chapters. 

M2-CO the first adduct bond energies are greater for Co, Ru, Pd, W, Ir, and Pt than V, Fe, Ni, Nb, and Mo. For the trimers, iron has a weaker bond than the other metals studied. For the tetramer and larger clusters the reactivity is controlled by the value of kn and no longer by the competition between uni molecular decomposition and collisional stabilization. The large cluster regime is not covered by this model used to make the correlation between kinetics and energeti cs. 

Arrhenius parameters calculated from the data in Tables 1-4 are shown in Table 5. The pre-exponential factors are all within the range expected for uni-molecular decompositions, with the exception of Co2(CO)6C2H2. The low value for its decomposition has been attributed to formation of a CO bridge in the transition state24. 

Fig. 8. (a) Energy diagrams for simple unimolecular decompositions (b) complex uni-molecular decompositions (c) simple bimolecular (metathesis) reactions (d) complex bimolecular reactions when one product channel is open and (e) when two product channels are open. 

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