Role of Na-Xe molecules in spin relaxation of optically pumped Na in Xe gas

A mixture of dense sodium vapor (number density [Na] {~} 10¹³ cm^-3), and buffer gases helium, xenon, and nitrogen is optically pumped to a high degree of spin polarization using a single-frequency single-mode tunable dye laser. The relaxation in the "dark" of the variables 〈Sz〉 and 〈→I·→S〉 is studied as a function of [Na] and buffergas pressures. For lower helium pressures (46-torr helium and 2-torr Xe) the dominant contribution to the relaxation of 〈Sz〉 in the presence of Xe comes from the "sticking" three-body collisions with He acting as the third body. This is further confirmed by studying the longitudinal magnetic field dependence of the spin-relaxation rate. At higher helium pressures (He 700 torr, and Xe 2 torr) the relaxation of 〈Sz〉 in the presence of Xe is mainly due to the "sudden" binary collisions between the Na and Xe, and the relaxation rate of 〈Sz〉 is independent of the longitudinal magnetic field. Significant hyperfine pumping is achieved by proper tuning of the laser. The temperature dependence of the relaxation of 〈→I·→S〉 and 〈Sz〉 is also discussed.