We report the results of resonant x-ray diffraction experiments performed on thick films of a biaxial liquid crystal made of achiral bent-core molecules. Polarization properties of forbidden reflections are observed as a function of the sample rotation angle $\phi$ about the scattering vector $Q$ for the first time on a fluid material. The experimental data are successfully analyzed within a tensor structure factor model by taking the nonperfect alignment of the liquid crystal into account. The local structure of the $B_2$ mesophase is hence determined to be $\mathrm{Sm}{C}_S{P}_A$.

• Received 28 May 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.227801