Vapor density. Note: Information

First and foremost, note that interest is in the nature of intramolecular dynamics of molecules in isolation. That is, observations must be made over a time scale where the molecule does not collide with others in the reaction vessel. Modern techniques allow very low pressures under which such measurements can be made. Most desirable among these methods are beam techniques in which molecules are studied in a low-density beam produced, for example, by vaporizing molecules in an oven. Experiments prior to this T>eam age (circa 1960) often inferred information about intramolecular dynamics from bulk data, which contained effects due to collisions, with resultant loss in accuracy. 

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