Diatomic molecules energy decomposition

Step 1 is the unimolecular decomposition of a diatomic molecule, and step —1 is a recombination of two atoms. This recombination is a highly exothermic reaction, and this energy will reside in the newly formed bond, which is thus highly excited. If this energy is not removed in the time of one vibration, the molecule will split up on vibration and recombination will not occur. If a collision occurs before the first vibration, then energy transfer takes place and the bond will be stabilized. The third body fulfils this function. This is more effective at high pressures and low temperatures. 

The decomposition of the diatomic molecule is the reverse of the recombination step, and so will also require a third body. The physical process involved is transfer of energy by collision to form an activated molecule which has enough energy to react. This is more efficient at high pressures and low temperatures. 

The homogeneous gas phase exchange reactions of diatomic molecules are described by activation energies that are much lower than the decomposition activation energies. The finding is that isotopic equilibrium is reached under reaction conditions in which the contributions from three centre atom—molecule reactions are negligible. 

The energy disposal and effective upper state lifetimes have been reproduced using classical trajectory calculations a quasi-diatomic assumption was made to determine the slope of the section through the upper potential energy surface along the N—a bond from the shape of the u.v. absorption profile. The only adjustable parameter was the assumption of a parallel transition in the quasi-diatomic molecule. In contrast, a statistical adiabatic channel model which assumed dissociation via unimolecular decomposition out of vibrationally and rotationally excited level in the ground electronic state (following internal con-... 

An important consequence of this situation is that recombination of atoms to form a diatomic molecule necessitates a molecule M, called third body, to remove the energy of bond formation. At equilibrium, this results naturally from the situation just discussed for decomposition by virtue of the principle of microscopic reversibility ... 

In the following three sections we shall discuss four applications of quantum mechanics to miscellaneous problems, selected from the very large number of applications which have been made. These are the van der Waals attraction between molecules (Sec. 47), the symmetry properties of molecular wave functions (Sec. 48), statistical quantum mechanics, including the theory of the dielectric constant of a diatomic dipole gas (Sec. 49), and the energy of activation of chemical reactions (Sec. 50). With reluctance we omit mention of many other important applications, such as to the theories of the radioactive decomposition of nuclei, the structure of metals, the diffraction of electrons by gas molecules and crystals, electrode reactions in electrolysis, and heterogeneous catalysis. 

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