Hironori Shimakura

Intermediate-range chemical ordering of cations in molten RbCl-AgCl

A first sharp diffraction peak (FSDP) is observed in the X-ray total structure factor of a molten mixture of RbCl-AgCl, while both pure melts of RbCl and AgCl do not exhibit FSDP individually. Molecular dynamics simulations were performed to investigate the origin of the FSDP with the polarizable ion model (PIM). Coexistence of covalent Ag-Cl and ionic Rb-Cl bonds leads the system to evolve intermediate range ordering, which is simulated by introducing the induced polarization in different ways between Ag-Cl with fully polarizable treatment based on Vashishta-Raman potential and Rb-Cl with suppression over-polarization in the nearest neighbor contribution based on Born-Meyer potential. The partial structure factors for both the Ag-Ag and Rb-Rb correlations, SAgAg(Q) and SRbRb(Q), show a positive contribution to the FSDP, while SAgRb(Q) for the Ag-Rb correlation exhibits a negative contribution, indicating that Ag and Rb ions are distributed in an alternating manner within the intermediate-range length scale. The origin of the intermediate-range chemical ordering of cations can be ascribed to the preferred direction of the dipole moments of anions in the PIM.

Determination of the structure of liquids containing free radical molecules: Inter-molecular correlations in liquid chlorine dioxide

X-ray diffraction spectra of liquid ClO2 at 204, 223, 248 and 273 K were measured at the BL04B2 beamline in the SPring-8 synchrotron radiation facility. The obtained structure factors are well reproduced by reverse Monte Carlo (RMC) structural modelling. With increasing temperature, the first peak located at around Q = 1.8 Å −1 slightly shifts to higher Q and the tail at the lower-Q side intensifies. In the pair distribution function, g(r), the intensity of the peak at around 3.2 Å that corresponds to the nearest-neighbour distance decreases with increasing temperature. The analysis of the RMC configurations shows that strong directional O–O interaction exists in liquid ClO2 and the instantaneous inter-molecular orientation depends on this interaction.

Dynamic Structure of a Molecular Liquid S0:5Cl0:5: Ab initio Molecular-Dynamics Simulations

The static and dynamic structures of a molecular liquid S0.5Cl0.5 consisting of Cl–S–S–Cl (S2Cl2) type molecules are studied by means of ab initio molecular dynamics simulations. Both the calculated static and dynamic structure factors are in good agreement with experimental results. The dynamic structures are discussed based on van-Hove distinct correlation functions, molecular translational mean-square displacements (TMSD) and rotational mean-square displacements (RMSD). In the TMSD and RMSD, there are ballistic and diffusive regimes in the sub-picosecond and picosecond time regions, respectively. These time scales are consistent with the decay time observed experimentally. The interaction between molecules in the liquid is also discussed in comparison with that in another liquid chalcogen–halogen system Se0.5Cl0.5.

Inter-molecular correlations in liquid Se2Br2

The structure of molecular liquid Se2Br2 was analyzed by means of reverse Monte Carlo structural modeling, using a calculation based on high-energy x-ray diffraction data. It was found that, between the optical isomers of L and D types, the number of L-D neighboring molecular pairs increases, while that of the L-L and D-D pairs decreases with increasing temperature. From this temperature dependence and from the relaxation mode analysis of quasi-elastic neutron scattering spectra, it is reasonable to assume that the presence of L-D pairs relates to genuine inter-molecular interactions while the L-L and D-D pairs appear due to geometrical packing of the gauche-shaped molecules.

Quasi-elastic neutron scattering of dense molecular liquid selenium bromide

Quasi-elastic neutron scattering spectra of liquid Se2Br2 at 298 K, 373 K and 473 K were measured by utilizing the cold-neutron disk-chopper spectrometer AMATERAS in J-PARC. The obtained dynamic structure factors are reproduced well by a two-Lorentzian model consisting of slow and fast modes. With increasing temperature, the maxima in the Q-dependence of the magnitude for both modes shift to a low Q direction, while the temperature dependence of the magnitude is opposite between slow and fast modes. The temperature dependence of the magnitude and the analysis of the energy width for these modes reveal that the fast mode is originated from dynamics in strongly interacted neighbouring molecules, while the slow mode is derived from inter-molecular dynamics without the strong interaction.

Intermolecular correlations of racemic mixtures – comparison between liquid S2Cl2 and Se2Br2

ABSTRACT Liquid chalcogen-halogen A2X2 (A: S, Se, X: Cl, Br) is a racemic mixture of enantiomers between left-handed (L) and right-handed (D) chiral molecules. The lone-pair orbital of the chalcogen atom significantly affects the molecular conformation and intermolecular interaction. The latter depends on the size of the orbital and number density. High-energy X-ray diffraction measurements and reverse Monte Carlo (RMC) structural modelling were performed for liquid S2Cl2 in addition to the previous structural analysis for liquid Se2Br2. By comparing the structures of the RMC model and hard-sphere Monte Carlo (HSMC) model, the effect of refinement on the experimental structure factor can be analysed. In this paper, nearest-neighbour intermolecular pairs are classified in terms of enantiomer pairs such as like-pair (L-L and D-D) and unlike-pair (L-D). As a result, the effect of a strong intermolecular attractive interaction is detected in Se2Br2 as increasing the number of like-pairs with geometrical advantages from HSMC to RMC, whereas that of an intermolecular repulsive interaction is observed in S2Cl2 as elongation of the averaged intermolecular S-S distance from HSMC to RMC. These results are consistent with the results of the ab initio molecular dynamics simulation for Se2Cl2 and S2Cl2.