Observation of three-body collisional transfer between atomic levels

Collisional $J$-mixing rates between the $J=0, 1, 2$ states of the $\mathrm{Sr}\left(5\mathrm{}{}_{}{}^3{}_{}{}^{}P_J^{}{}_{}{}^{}\right)$ multiplet have been measured in the presence of rare-gas perturbers. For Kr and Xe pressures above 100 Torr, the rates are dominated by a component which is quadratic in pressure. We believe this very unusual behavior is brought about by the simultaneous interaction of a Sr atom with two perturbers and not by excimer formation.