Nature of the Reagent Neutral or Charged Species

Historically the experimental techniques that have been developed in the field of very low temperature chemistry have first concerned charged species. As mentioned in the Introduction, the first reason for this was that ion-molecule reactions were thought to be the main route to interstellar molecule synthesis.The second reason, and maybe the most important 

Collisions involving electrons deserve a special discussion since, due to their very low mass, KEcm is essentially the electron kinetic energy. It is rather easy, especially with laser techniques, to generate electrons of very low energies which do not relax efficiently to the higher neutral gas temperature. It is therefore quite simple to study cross sections at low KEcm for processes such as electron attachments but such studies have been conducted mostly with internal temperature of the molecules close to 300 K. 

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