Local structure and orientational ordering in liquid bromoform

Abstract

The neutron diffraction data of liquid bromoform (CHBr₃) at 25°C was analysed using the Empirical Potential Structure Refinement technique in combination with H/D isotopic substitution. Compared to liquid chloroform (CHCl₃), CHBr₃ displays more spatially defined intermolecular contacts. A preference for polar stacking with collinear alignment of dipole moments is observed for the most closely approaching CHBr₃ 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 CHBr₃ is smaller than that of CHCl₃. The net antiparallel alignment of dipole moments in CHBr₃, as suggested by dielectric spectroscopy, must be due to weak but persistent long-range orientation correlations in CHBr₃, which counteract the local polar stacking.

GRAPHICAL ABSTRACT

KEYWORDS:

• Bromoform
• haloforms
• neutron diffraction
• Kirkwood correlation factor

Acknowledgments

We thank the Royal Society for a University Research Fellowship (CGS), the EPSRC and Durham University for a PhD studentship (JJS), the ISIS neutron source for granting access to the SANDALS beamline, S. Imberti and S. Callear for help during the neutron diffraction experiment, and A. Soper for helpful discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Engineering and Physical Sciences Research Council: [DTA studentship for JJS]; Royal Society: [grant number UF100144].