We report on the interplay between the short-range order of molecules in the liquid phase of 1,1,2,2-tetrachloro-1,2-difluoroethane and the possible molecular conformations, trans and gauche. Two complementary approaches have been used to get a comprehensive picture: analysis of neutron-diffraction data by a Bayesian fit algorithm and a molecular dynamics simulation. The results of both show that the population of trans and gauche conformers in the liquid state can only correspond to the gauche conformer being more stable than the trans conformer. Distinct conformer geometries induce distinct molecular short-range orders around them, suggesting that a deep intra-and intermolecular interaction coupling is energetically favoring one of the conformers by reducing the total molecular free energy.

The thermal conductivity ͑T͒ of the orientational glass state of 1,2-difluoro-1,1,2,2-tetrachloroethane ͑CFCl 2 -CFCl 2 , Freon 112͒ and cyanocyclohexane ͑C 6 H 11 CN͒ has been measured under equilibrium pressure within the temperature range 2-100 K. The results show that the soft-potential model is able to account for low-temperature data and, indeed, quantitative agreement of all data considered is found within this realm. The details beyond such temperatures are heavily dependent on chemical details and a large plateau is observed for Freon 112 which is rationalized in terms of resonant scattering of phonons by simple oscillators. Such a view is given additional support by the presence of a strong low-frequency feature in the generalized frequency spectrum of the former material as proven by inelastic neutron-scattering spectroscopy.

The thermal conductivity, specific heat, and specific volume of the orientational glass former 1,1,2-trichloro-1,2,2-trifluoroethane (CCl 2 F-CClF 2 , F-113) have been measured under equilibrium pressure within the low-temperature range, showing thermodynamic anomalies at ca. 120, 72, and 20 K. The results are discussed together with those pertaining to the structurally related 1,1,2,2-tetrachloro-1,2-difluoroethane (CCl 2 F-CCl 2 F, F-112), which also shows anomalies at 130, 90, and 60 K. The rich phase behavior of these compounds can be accounted for by the interplay between several of their degrees of freedom. The arrest of the degrees of freedom corresponding to the internal molecular rotation, responsible for the existence of two energetically distinct isomers, and the overall molecular orientation, source of the characteristic orientational disorder of plastic phases, can explain the anomalies at higher and intermediate temperatures, respectively. The soft-potential model has been used as the framework to describe the thermal properties at low temperatures. We show that the low-temperature anomaly of the compounds corresponds to a secondary relaxation, which can be associated with the appearance of Umklapp processes, i.e., anharmonic phononphonon scattering, that dominate thermal transport in that temperature range. C 2015 AIP Publishing LLC. [http://dx

The thermal conductivity κ(T ) of the fully ordered stable phase II, the metastable phase III, the orientationally disordered (plastic) phase I, as well as the nonergodic orientational glass (OG) phase, of the glass former cyclohexanol (C 6 H 11 OH) has been measured under equilibrium vapor pressure within the 2-200 K temperature range. The main emphasis is here focused on the influence of the conformational disorder upon the thermal properties of this material. Comparison of results with those regarding cyanoclyclohexane (C 6 H 11 CN), a chemically related compound, serves to quantify the role played by the terminal groups -OH and -CN on the phonon scattering processes. The picture that emerges shows that motions of such groups do play a minor role as scattering centers, both within the low-temperature orientationally ordered phases as well as in the OG states. The results are analyzed within the Debye-Peierls relaxation time model for isotropic solids comprising mechanisms for long-wave phonon scattering within the OG and orientational ordered low-temperature phases, as well as others arising from localized short-wavelength vibrational modes as pictured by the Cahill-Pohl model. By means of complementary neutron and Raman scattering we show that in the OG state the energy landscapes for both compounds are very similar.

The study of how both steric and electrostatic interactions affect the structure of liquids formed by quasitetrahedral molecules has been undertaken in this work. We have studied trichlorobromomethane (CBrCl3) and dibromodichloromethane (CBr2Cl2), both displaying a dipole along their C3v and C2v molecular symmetry axes, respectively. The short-range order of the liquid state has been determined using neutron diffraction experiments that were modeled through the reverse Monte Carlo (RMC) technique. To study changes in steric effects due to the distortion of the tetrahedral symmetry, we have compared our results with a previous RMC modeling of carbon tetrachloride (CCl4). The subtle effects of the dipole in the structure of the liquid have been determined using a set of molecular dynamics simulations with and without atomic partial charges, being the force field validated via comparison with the diffraction data. In a first approximation, neither steric nor electrostatic interactions are able to modify the molecular ordering of a fully tetrahedral liquid such as CCl4. A more detailed analysis indicates that, although the interaction between dipoles does not have appreciable effects when aligned along the C3v molecular axes, as for the CBrCl3, it enhances the antiparallel orientation of dipoles when it is oriented along the C2v axes, as in the case of CBr2Cl2.Postprint (published version