The possible symmetries of the biaxial nematic phase are examined against the implications of thepresently available experimental results. Contrary to the widespread notion that biaxial nematicshave orthorhombic symmetry, our study shows that a monoclinic (C_(2h))symmetry is more likely tobe the case for the recently observed phase biaxiality in thermotropic bent-core andcalamitic-tetrapode nematic systems. The methodology for differentiating between the possiblesymmetries of the biaxial nematic phase by NMR and by IR spectroscopy measurements ispresented in detail. The manifestations of the different symmetries on the alignment of the biaxialphase are identified and their implications on the measurement and quantification of biaxiality aswell as on the potential use of biaxial nematic liquid crystals in electro-optic applications arediscussed.
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