Collisional Angular Momentum Mixing in Rydberg States of Sodium

Collisions with rare-gas atoms are observed to produce a lengthening of the lifetime of the highly excited ($n=5-10\mathrm{}$) $d$ states of Na. The effect is interpreted as collisional angular momentum mixing of the $d$ state with $l>\mathrm{}2\mathrm{}$ states; thus the average lifetime of all states for which $l>~2$ is observed. The cross section for the process appears to increase as the geometrical cross section of the excited atom.