Local Structure and Orientational Ordering in Liquid Bromoform

<p>The neutron diffraction data of liquid bromoform (CHBr<sub>3</sub>) at 25°C was analysed using the Empirical Potential Structure Refinement technique in combination with H/D isotopic substitution. Compared to liquid chloroform (CHCl<sub>3</sub>), CHBr<sub>3</sub> displays more spatially defined intermolecular contacts. A preference for polar stacking with collinear alignment of dipole moments is observed for the most closely approaching CHBr<sub>3</sub> molecules, although to a lesser extent than in chloroform. Consistent with this and in line with dielectric spectroscopy, the Kirkwood correlation factor from the structural model of CHBr<sub>3</sub> is smaller than that of CHCl<sub>3</sub>. The net antiparallel alignment of dipole moments in CHBr<sub>3</sub>, as suggested by dielectric spectroscopy, must be due to weak but persistent long-range orientation correlations in CHBr<sub>3</sub>, which counteract the local polar stacking.</p>