Reactive collision dynamics exoergic reaction

When a reaction is studied in the bulk gas phase, the nascent products soon collide with other molecules, energy is transferred upon collision (thus becoming effectively partitioned among all molecules), and the overall reaction exoergicity is finally liberated in its most degraded form, i.e., heat. In macroscopic terms, the reaction is exothermic, i.e., A/f < 0. The microscopic approach of molecular dynamics, however, is concerned with the outcome of the individual reactive collisions. The experimental challenge, as discussed in Section 1.2.5, is to arrest the collisional relaxation of the nascent reaction products and to probe them as they exit from the reactive collision. In this sense, it is customary to speak about the nascent or newborn reaction products. 

Molecular dynamics in its purist approach tries to seek out (and understand) the truly elementary events. Thus it is more interested in the left than in the right panels of Figure 1.2. It is, however, concerned not only with the primary reactive collision process but also with the subsequent non-reactive, inelastic energy-transfer steps that take the system from the nascent distribution of products to the fully relaxed one. The Cl + HI system is not exceptional. Many exoergic reactions release a substantial part of their energy into internal modes of product excitation." A key problem facing us is to understand this observation in terms of the forces that act during the collision. In this introductory case study we use a model. 

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