Knowledge Bank

1,3,5-Trichlorobenzene crystallizes in space group $P212121(D24)$ with four molecules per unit cell. The twelve librational modes are divided evenly among the four irreducible representations of factor group $D2$, and are joined by the nine optical translatory vibrations which are distributed $3A+2B1+2B2+2B2+2B3$. These lattice modes are all Raman active and occur below $100cm-1$, permitting partial identification by single crystal laser Raman polarization data. The assignments are assisted by comparison with corresponding data secured for the isomorphic crystal 1,3,5-tribromobenzene. The temperature dependence of the optical modes is reported, and the relation to the chlorine nuclear quadrupole resonance spectrum of 1,3,5-trichlorobenzene is discussed.