The influence of collisions on high Rydberg members

This is particularly true with regard to collisions. Care must be taken when performing experiments on high series members to investigate whether collisions between atoms (especially if other atomic species, e.g. a noble gas used as a buffer gas to impede diffusion of the sample, is present) can influence the result. 

The most dramatic effect of collisions is to induce mixing between nearby excited states of the atom, whose presence would not normally manifest itself. Consider for example a spectrum in which a regular Ryd- 

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