Optically pumped atomic spin orientation and the law of mass action for 2Cs ⇄ Cs₂

The effect of optically pumped atomic spin orientation on the atom-dimer equilibrium in cesium vapor has been observed. Such a shift in equilibrium was predicted over two decades ago and is due to the redistribution of spin-determined bonding and antibonding collision trajectories. Orientation of the total spin angular momentum of 6 ²S^1/2 ground state Cs atoms in the vapor phase was produced by optical pumping with a tunable cw dye laser. A decrease in the equilibrium molecular density resulted and was measured using laser induced fluorescence from the B ¹II_u state. The shift in equilibrium is a function of the degree of atomic orientation and could be observed in the temperature range 383-421 K for cesium vapor in a glass cell which also contained a He-N₂ buffer gas mixture with a composition ratio of 9:1.