Collisional depopulation of excited Nasstates by He, Ar, and Xe

The authors have measured the collisional depopulation cross sections of Na $s$ states from $n=6\mathrm{} \mathrm{to} 11$. The maximum cross sections observed for He, Ar, and Xe, respectively, are ∼20, 20, and 100 ${\mathrm{\AA }}^2$. The cross sections rise from ∼0.1 ${\mathrm{\AA }}^2$ at $n\sim 6$ to a plateau at $n\sim 10$. The small size of the cross sections suggests that the process proceeds via the interaction of the ${\mathrm{Na}}^{+}$ core with the rare-gas atom. Specifically, this short-range interaction produces a transient dipole on the rare-gas atom which efficiently couples Na states of different $n$. This is an entirely different mechanism than that responsible for the collisional $l$ mixing previously reported.