Dissociation energy fragment approach

Atomic metal ion-hydrocarbon reactions bond dissociation energies for fragments, 15,16t endothermic reactions, 13,15,17f Atomic transition metal ion reactions development of approach for real-time measurements of dissociation kinetics, 39 ion beam apparatus, 12,14f studies of... 

However, the classical approach should not be used for a quantitative interpretation of the experimental results for single-quantum vibrational predissociation. The classical process, which should show the correspondence with the quantiun one, is the cleavage of a bond under a condition when the quantum of energy transferred to this bond from a diatomic fragment, hQ, is much smaller than the dissociation energy, Ej, of the bond, i.e. h l . This condition does not contradict the classical limit,... 

The Rice-Ramsberger-Kassel approach assumes that the activated molecule has a certain amount of vibrational energy spread among the various vibrational degrees of freedom of the molecule. Then the probability of one particular mode of vibration acquiring so much of this energy that the vibration leads to dissociation into fragments is calculated. 

Table 4 give the dissociation energies of each complex in its fragments and CN, evaluated in this way by the MRPT2 method. The error bar of the perturbational approach is reduced to a few kcal.mole. However, the conclusions previously obtained at the CASPT2 level, namely a decreasing stability of the MNC and MCN complexes from early to late transition metals and a possible preference for the cyanide forms in the case of median cations, like iron Fe, are still valid. 

Thus, if any two of the three heats of formation are known, the third can be calculated from the measured dissociation energy, DE. Many heats of formation derived using this approach have been reported. However, the validity of this method depends upon a rapid dissociation of the molecular ion. What is actually measured is the appearance energy, AE, of the product ions which is always greater than DE. Ions prepared just above their dissociation threshold often fragment very slowly (e.g. <10" s ) so that no A" ions will be observed since ions are collected in just a few microseconds after their formation. It is not until the ion energy reaches a level at which the dissociation rate constant, k, exceeds lO s- that A+ ions are observed. An effective means for circumventing this problem is to measure the dissociation... 

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