Optical Pumping and Collisional Relaxation in theP122Ground State of Thallium

The $^{2}P_{\frac{1}{2}}$ ground state of thallium has been optically pumped in the presence of various buffer gases. The measured cross sections for the destruction of the electron polarization are small (${10}^{\ensuremath{-}19}$ to ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$), verifying the selection rule ${M}_{J}\ensuremath{\nrightarrow}\ensuremath{-}{M}_{J}$ for the adiabatic contributions and demonstrating the strong dependence of the nonadiabatic contributions upon the multiplet energy separation.