Symmetry diagnostic

System Minimal symmetry (diagnostic symmetry elements) Relations between edges and angles of unit cell Lattice type Numbering in Figure 20... 

Fig. 15.—X-ray diffraction pattern from a polycrystalline and well-oriented fiber of sodium pectate (13), diagnostic of 3-fold helix symmetry.

Polarized absorption spectroscopy is a powerful diagnostic tool for investigating molecular structure and the symmetry considerations discussed above can be extended to the situation where the incident light is polarized along a particular direction. The strength of the interaction of the transition dipole moment, A(. -,k , with the electric vector of the... 

Most chemists would accept the general statement that optically active molecules are those without an alternating axis of symmetry, as adequate. This is perhaps a reliable diagnostic of natural optical activity, but it offers no explanation of the Faraday effect, which shows that achiral molecules become optically active in an applied magnetic held. 

Raman spectroscopy has been an excellent diagnostic tool in the study of the Ceo molecule and its salts, because of the high symmetry these substances possess. In the case of C6o- which has a center of symmetry, the gerade modes are observed only in the Raman spectrum. Furthermore, the materials are excellent Raman scatterers. 

The symmetry of the Iv(6) distribution about the 6 = 90° plane remains a diagnostic test for complex formation. Moreover, the anisotropy of the / ( ) distribution can be used [44] to determine the partitioning of final angular momentum between L and J and therefore the rotational energy of the diatomic product AB. Unsymmetric scattering of the product about 6 = 90° indicates a direct reactive mechanism, and observations of the preferred direction of recoil provide important evidence concerning the character of the reactive collisions. 

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