Reaction Cross Section Ion-Molecule Systems

The hard-sphere model, as described in Chapter 2, only accounted in a qualitative fashion for the mass, momentum, and energy transport that underlie the phenomena of diffusion, viscous flow, and heat conduction. For systems other than monatomic gases, the model was of limited utility. Thus, its failure to predict reasonable values of the Arrhenius -factor is to be expected. 

An understanding of reaction cross sections is only possible by considering some aspects of the dynamics of molecular interaction. Naturally not all molecular collisions lead to reaction. There is always the possibility (often quite substantial) of inelastic collision. However, we shall only discuss reactive events. 

Simplest to describe are those systems in which there is no barrier to reaction. Exoergic ion-molecule reactions fall into this category. Due both 

This term denotes that electronic energy is released in the reaction, i.e., the products are more stable than the reactants. It is the equivalent, in discussions of chemical dynamics, to the familiar word exothermic which is used to indicate that heat is evolved in a reaction at constant temperature. 

To understand the behavior of Q E) requires considering the effect of the long-range attractive forces on the reactants trajectories. This is 

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