Product energy distribution impulsive model

A widely-used model in this class is the direct-interaction with product repulsion (DIPR) model [173—175], which assumes that a generalised force produces a known total impulse between B and C. The final translational energy of the products is determined by the initial orientation of BC, the repulsive energy released into BC and the form of the repulsive force as the products separate. This latter can be obtained from experiment or may be assumed to take some simple form such as an exponential decay with distance. Another method is to calculate this distribution from the quasi-diatomic reflection approximation often used for photodissociation [176]. This is called the DIPR—DIP model ( distributed as in photodissociation ) and has given good agreement for the product translational and rotational energy distributions from the reactions of alkali atoms with methyl iodide. 

Strong parallels are observed between the reactions of Yb and alkaline earth metals with halomethanes [399]. The trends in the energy disposal of the YbX product accord well with the impulsive photodissociation model [Sect. 3.1.3(c)]. The product vibrational distributions of the YbX from Yb + RX, when plotted against fv, show a marked dependence on the identity of R and an insensitivity to the nature of X (for Br and I), the distributions shifting to higher fv in the sequence CH3, CH2X, CF3 (Fig. 12). 

Two other contributions (Grice, 1970 Grice and Hardin, 1971) have also incorporated orientation effects in an impulsive model, in this case involving only two hard spheres, which was applied to the alkali-iodine molecules M + RI rebound reactions. Experimental results on the 0+ + H2/D2/HD reaction have been compared (Gillen et al 1973) to predictions of a sequential encounter model that also represents the atoms as hard spheres. Product angular distributions and their isotopic dependences are well represented by the model, which however, is less useful in predicting collision energy behaviours. 

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