Spin relaxation of of rubidium atoms induced by collisional modification of the Rb hyperfine interaction

Spin relaxation of Rb atoms induced by collisional modification of the hyperfine interaction has been measured for ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ in He, Ne, and Ar buffer gases at high magnetic field. The relaxation rates at 40 kG are 0.028 ${\sec }^{-1\mathrm{}}$ ${\mathrm{Torr}}^{-1\mathrm{}}$ for ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ in He, 0.029 ${\sec }^{-1\mathrm{}}$ ${\mathrm{Torr}}^{-1\mathrm{}}$ for ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ in Ne, and 0.041 ${\sec }^{-1\mathrm{}}$ ${\mathrm{Torr}}^{-1\mathrm{}}$ for ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ in Ar. The corresponding relaxation rates for ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ are approximately 4.9 times larger, in accord with theory. Cross sections for the binary $\delta a\left(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{I}}\right)$ collisional interaction are estimated to be $\sigma \left(\delta a\right(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{I}}\left)\right)(\mathrm{Rb}-\mathrm{He})=2.3\mathrm{}\times {10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$ and $\sigma \left(\delta a\right(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{I}}\left)\right)(\mathrm{Rb}-\mathrm{Ne})=1.4\mathrm{}\times {10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$. Anomalous relaxation, $R^{*}$, is present in the same degree at 40 kG as at low magnetic field, lending strong support to earlier attributions of $R^{*}$ to the $\delta a\left(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{I}}\right)$ interaction in Rb-atom-noble-gas-atom van der Waals molecules.