Equivalence and conservation rules for the total integral cross section in molecular collisions

The rule of conservation of the total integral cross section o_Tj) is described in a general way using the opacity function. An equivalence rule which states that at the same initial kinetic energy, the total integral cross section from the initial state j is equal to that from the initial state j, i.e., o_Tj) is also presented. Both rules are demonstrated with numerical examples in the He + H₂ collision system and counter-examples are also presented. Possible uses of the rules in the inversion of the intermolecular surface and as an experimental tool are also discussed.