Impulsive reaction model angular distributions

As mentioned previously, the modified spectator stripping model (polarization model) of Herman et al. [103] explains the velocity distribution of products very well but does not predict the angular distribution, whereas the DIPR model explains both. Thus there had been no full comparison between the two models until Chang and Light [113] refined and extended the polarization model to yield the angular distribution of products as well. 

The refined model is also a classical mechanical model of the reactive collision event, in which both the long-range polarization and short-range repulsive forces are taken into account. In doing so, the model assumes that the repulsive forces are impulsive at the reaction radius , and for this reason the model is referred to as the impulsive model . 

The procedure for calculating the final trajectory and the product angular and energy distributions is as follows. First, the incoming trajectory (deflection Xr ) is determined classical mechanically as a function of the initial impact parameter 60 of A with respect to the centre-of-mass of BC, the initial relative kinetic energy Tq, and the long-range spherically symmetric potential n c ( ) which acts between the centres-of-mass of A and BC. 

Finally, the final kinetic energy Tf and the deflection angle xh for the outgoing trajectory are determined, assuming the spherically symmetric potential b - c ( ) acting between the separating products AB and C. The total deflection x is then given by 

The long-range attractive potential V r) = —ae /2r was used for both Va B c and b - c. as in the polarization theory. 

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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. 

In this case the character of the angular and velocity distribution of a direct mode reaction may be well described by simple dynamical models, and one of the most used for the title reaction is that of the electron jump mechanism the basic assumptions of which follow Herschbach s idea of the so called diatomic reflecting approximation [4]. The M atom induces, by an electron jump, a vertical transition from the BC to the BC repulsive potential leading to the impulsive separation of... 

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