Alignment and orientation studies experimental

We will also mention that, turning the system of coordinates, the quantity 0 transforms according to the formula 

One of the practical applications of the optical polarization of molecular angular momenta is the investigation of the stereochemical forces in the process of molecule-atom collisions. The most complete information on the dependence of atom-molecule interaction potential on the orientation of the molecule with respect to the relative collision velocity can be obtained by the method of molecular beams, and often in conjunction with inhomogeneous magnetic and electric fields which orient the molecules. Such investigations are undoubtedly very complex, and their realization rather costly. To convince oneself of it one might just peruse the Proceedings of the First Workshop on Dynamic Stereochemistry in Jerusalem in 1986 [66] see also [67, 341], 

At the same time it is possible to obtain sufficiently interesting information on the dynamics of collisions by means of technically simpler measurements of the polarization of laser-induced fluorescence at excitation of molecules in bulk. A short account of such investigations is given in [288]. 

The simplest method consists of investigating the collisional depopulation of a laser excited rovibronic level, i.e. of measuring the rates and cross-sections of the collisional relaxation of its population bPo- The relaxation rate Tk of polarization moments bPQ of various rank K may be represented, in the case of isotropic collisions, as follows  

He and Na atoms [116]. Table 2.2 presents example results of [24, 312] in which the o of a given rovibronic level of NaK and K2 molecules were determined from Stern-Volmer graphs. Such large cross-sections indicate that the partners of collisions interact fairly efficiently at comparatively large distances. 

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