In the high pressure limit the key problem is how to calculate the rate coefficient k(E)in the unimolecular decay reaction
(3). There are a lot of theories dealing with this problem; among them the most common one was developed by Rice,
Ramsperger, Kassel, and Marcus, known as RRKM theory. In this theory, one focuses on the transition state [2],
A
∗ → A
̸= → Products, (12)
where A
̸= is transition state (also called activated complex).