ABSTRACT

In the previous chapter, we argued that the chemical kinetics equations describing time evolution of different chemical species arise naturally from the microscopic motion governed by the underlying potential energy landscape. Deep wells on the potential energy surface (deeper than the thermal energy kB T ) represent molecular species. While most of the time is spent within those wells, a jump from one well to another takes place every once in a while. Such jumps are what we refer to as chemical reactions. Adopting this view, we no longer care about the exact molecular configuration (i.e., the exact position of the system on the energy landscape) but rather characterize the system’s state by specifying the well it occupies at any given time. This, in particular, implies that the system always occupies some well, an assumption that can be valid only if the duration of the jump itself is much shorter than the typical time spent inside a well and so the time spent in transit between wells can be neglected. While such a picture often provides a very good description of many molecular phenomena, the transit time is also a very interesting quantity to consider: It will be studied in the next chapter.