Electronic spin relaxation of the4S122state of K induced by K-He and K-Ne collisions

Electronic and nuclear spin relaxation of optically pumped K atoms has been measured in the presence of He and Ne gases. The nuclear-spin-independent cross sections for the destruction of electronic spin polarization in the $4{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ ground state of K are $\sigma \left[\gamma \right(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{N}}\left)\right](\mathrm{K}-\mathrm{He})=8.0\mathrm{}\times {10}^{-25\mathrm{}}$ ${\mathrm{cm}}^2$ and $\sigma \left[\gamma \right(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{N}}\left)\right](\mathrm{K}-\mathrm{Ne})=141\mathrm{}\times {10}^{-25\mathrm{}}$ ${\mathrm{cm}}^2$. The diffusion coefficients of K in He and Ne, corrected to 273 K, are $D_0(\mathrm{K}-\mathrm{He})=0.35\mathrm{}$ ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$ and $D_0(\mathrm{K}-\mathrm{Ne})=0.19\mathrm{}$ ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$. All measurements have an estimated uncertainty of ±10%. The relaxation of K is shown to be strongly affected by an anomalous process which is attributed to the modification of the K hyperfine interaction induced by the formation of K-He and K-Ne van der Waals complexes.