AbstractIn cubic crystals the infrared‐active triply degenerate modes split into anLOand a doubly degenerateTOmode. For crystals with T symmetry, first‐order spatial dispersion splits the polarTOmodes into a set of two circularly polarized T+and T−modes whose frequencies have only a small separation. Using incoherent high‐resolution Raman spectroscopy (a tandem Fabry–Perot Raman double monochromator of limiting resolution 0.005 cm−1), we have measured the splitting of the low‐energy TO lattice modes in the optically active material sodium chlorate.Experiments were performed in various scattering geometries to separate the optical Raman‐active modes of different symmetries (A, E, LOandTOmodes). Furthermore, the difference in the Raman response of theT+andT−modes to left or right circularly polarized incident light was detected and analysed.We measured for the three low‐energy TO modes (77, 98 and 125 cm−1atT= 6 K) a splitting of 0.08, 0.08 and 0.105 cm−1respectively in a right angle geometry and 0.11, 0.11 and 0.135 cm−1respectively in a backscattering geometry (an increase in agreement with a shift proportional t