review temperature range in collisions

[epassaro]

is that a sensible temperature range? This should be somewhere better documented.

Originally posted by @wkerzendorf in https://github.com/tardis-sn/carsus/pull/191#discussion_r497477416

[hrithik18236]

What is the collision temperature referring to so that I may do some research about it?

[chvogl]

@hrithik18236 One important process in the ejecta of exploding stars is the excitation of atoms by collisions with electrons. The excited atoms can then emit photons, which we can use to learn about the properties of the exploded star. The rate of these excitations can be calculated based on the collision strengths. We use tables of these collision strengths in our simulation. The "collision temperatures" are the temperatures for which we tabulate these values.