Zeitschrift für Naturforschung / A / 28 (1973)

(Z. Naturforsch. 28 a, 1543-1553 [1973] ; received 7 May 1973) Nonequilibrium alignment phenomena in gases of polyatomic molecules (Senftleben-Beenakker effect, flow birefringence) have been studied extensively during the last decade. Similar effects should also exist for atoms with nonzero electronic orbital angular momentum. The WaldmannSnider equation (considered as Boltzmann equation for reacting mixtures) is used to derive an expression for the tensor polarization caused by a flow field in such atomic vapors. As a simple special case 2P-atoms are treated as an effective two level system (fine structure doublet). They can be tensor-polarized in the state with j = 3/2. An ansatz is made for the nonspherical inter­ action potential between 2P-atoms. The scattering amplitude is calculated in first order Born approximation which is reasonable for the high temperatures necessary. The relevant cross sections and collision integrals are evaluated. The temperature dependence of the alignment and its order of magnitude are discussed. Although the effect is rather small it should be detectable by optical methods (flow birefringence). The connection of flow birefringence and collisional alignment is elucidated.