BIREFRINGENCE AND OPTICAL-ACTIVITY OF [N(CH3)4]2ZNCL4

The birefringence and optical activity of [N(CH3)4]2ZnCl4 in phases I, II, III and IV have been measured with a high-accuracy universal polarimeter for six samples, all with different orientations. The birefringences clearly show the phase transitions. From the data, the diagonal components g(ii) of the second-rank gyration pseudotensor could be determined and the off-diagonal components g(ij) can be estimated. The results can be interpreted with the mesoscopic description of Dijkstra, Janner and Meekes which is especially applicable to the incommensurately modulated phase (II), but also to the multidomain monoclinic phase (IV).