The structure of liquids containing molecules with non-regular tetrahedral shape: methylene-iodide and dichloro-dibromo-methane

measured by the PSD

Over the past decade, detailed investigations of liquids containing symmetric molecules have been conducted in our department. Following XCl₄-type molecules which possess perfect tetrahedral symmetry, we continued our studies of liquids containing molecules with slightly distorted tetrahedral symmetry. In the present experiments, (deuterated) methylene-iodide (CD₂I₂) and a non-hydrogenous methane derivative, dichloro-dibromo-methane (CCl₂Br₂) have been considered. Exploiting the neutron diffraction data, we wished to characterize correlations between molecular orientations in the liquids.  

Neutron diffraction experiments at room temperature have been carried out, applying a wavelength of 1.069 Å. Raw intensities were corrected for background and detector efficiency, after which treatment, Reverse Monte Carlo (RMC) calculations were conducted which were able to refine normalization and background corrections to the data. Figure 1 shows experimental and RMC simulated total scattering structure factors of both liquid CD₂I₂ and CCl₂Br₂. (It is worthwhile noting that the latter material transformed into a-as yet, unnoticed-gel-like disordered phase by the end of the measurement, at a temperature of about 291 K.)

Recommended articles:

P. Jóvári, Gy. Mészáros, L. Pusztai, E. Sváb, The structure of liquid tetrachlorides CCl₄, SiCl₄, GeCl₄, TiCl₄, VCl₄, and SnCl₄, J. Chem. Phys. 114 (2001)  8082-8090

P. Jóvári, Gy. Mészáros, L. Pusztai, E. Sváb: Neutron diffraction studies of some simple molecular systems: Si2Cl6, CBr3D and CD3I. Applied Physics A74 (2002) S1354-S1356

Pothoczki Sz., Temleitner L., Jóvári P., Kohara S., Pusztai L., Nanometer range correlations between molecular orientations in liquids of molecules with perfect tetrahedral shape: CCl₄, SiCl₄, GeCl₄ and SnCl₄, J. Chem. Phys.; 130 (2009) 064503