Bond dissociation energ

Bond dissociation energy, D (Section 5.8) The amount of energ r needed to break a bond homolytically and produce two radical fragments. 

The indirect method was put forward by Stevenson in it the appearance potentials of the same ion produced from two different but related molecules are measured, and their difference is combined with thermochemical data to give the required dissociation energ) It is thus possible to calculate bond dissociation energies from appearance potentials and thermochemical data without a knowledge of ionization potentials. The essence of the method is to produce as the non-ionized partner in a dissociative ionization process of the type... 

The dynamics of the H-I-C2H4 association step deposits the 40 kcal/mol reaction exothermicity and the 30 kcal/mol relative translational energy non-randomly in the energized C2H5 radical, with the C-H bond, that is formed, preferentially excited as compared to the other C-H bonds. The expectation is that this non-random excitation may lead to an initial dissociation rate that is larger than that of RRKM theory. However, C2H5 is... 

Chemical activation and fall-off. Gas-phase reactions that form an energized product cause particular difficulty in kinetic model-construction. For example, in Reaction (1) the unstable product will be formed with excess energy (due to the exothermicity of the bond-forming addition reaction), that it will rapidly dissociate to ethyl acetate + allyl radical, Reaction (3). 

When clusters comprise several loosely bound molecules, the atoms within each molecule are held together by strong bonds while the molecules themselves are attracted to neighboring molecules by weak bonds. This discrepancy in forces translates into disparities in the respective vibrational frequencies. In the case of the HF dimer the two H—F vibrational frequencies are ca. 4000 cm while the four van der Waals frequencies are 480, 400, 210, and 150 cm (Quack and Suhm, 1991). The consequence of these different frequencies and forces is that energy cannot flow as freely among constituent units of the cluster as it can within each molecule. That is, there are bottlenecks in the phase space which means that IVR is inhibited. Thus, cluster dissociations, especially when energized by infrared radiation, provide some of the rare example of nonstatistical decay. 

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