Collisional depopulation of RydbergPstates of rubidium at thermal energies

We have measured total cross sections for the collisional depopulation of high-lying $\mathrm{nP}$ states ($12\le n\le 22$) of rubidium induced by thermal collisions with ground-state rubidium or rare-gas atoms. It is observed that for $n\ge 14$ the rubidium-rare-gas cross sections do not vary with the principal quantum number, contrary to previous hypotheses. Our results are discussed using the simple argument of quasifree behavior of the valence electron involving either an elastic-scattering or a binary-encounter approach. However, the disagreement observed between the experimental and the computed cross sections suggests that a three-body approach is generally needed for a good understanding of collisional processes involving highly excited states.