Rebound scattering

These elements are scattered throughout the universe when massive stars end their lives. When there is no fuel left to burn, the core collapses once again, and there is nothing to stop it. A shock wave from this collapse causes a rebound that fuels an enormous explosion a supernova. The outer layers of the star are blown out into space, and the energy that is released triggers new nucleosynthesis reactions, which make the heavy elements beyond bismuth - up to uranium, and at least a little beyond. 

Product PM has backward scattering with maximum very close to 180°, so that PM emerges from the reactive collision rebounding almost totally backwards from the direction in which P was originally moving. Likewise, N rebounds backward from the original direction of MN. 

Reactions showing backward scattering have small impact parameters and cross sections. The mechanism is called rebound because P hits MN head on, pulls M away from N and, under the influence of the repulsive forces between M and N, PM moves almost totally backwards. N also rebounds backwards from PM under the same repulsive forces, and returns only slightly deflected from its original path (Figure 4.12). 

Repulsive surfaces are associated with the backward scattering of a rebound mechanism, in which A collides with BC in a head-on collision and AB rebounds backwards. 

The rebound mechanism showing backward scattering and small cross sections is typified by... 

The back reaction will have the exact reverse characteristics. The activated complex will lie in the exit valley, and reaction will be enhanced by high vibrational energy. There will be high translational energy in the products, the cross section will be small, and the molecular beam contour diagram will show predominantly backward scattering, typical of a rebound mechanism. 

Wilson and Herschbach [75] have discovered several systems, involving polyhalide molecules, where the peak intensity of the scattered product corresponded to wide c.m. angles and the dynamics is intermediate between the limiting cases represented by rebound and stripping. The preference for forward scattering could be correlated with large values for aR. E was estimated to lie between 10 and 30% of the total energy. 

This is a classical rebound reaction. When sodium is in the ground state, 84 % of the reaction product NaBr is scattered in the backward hemisphere. This phenomenon arises from two factors a close approach distance for the electron transfer to proceed, and a steric factor, where sodium must approach the Br end of CH3Br to bounce back as NaBr. If approaching the wrong end of CH3Br, sodium does not react. This leads to the concept of the acceptance angle for the reaction [163]. 

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