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

Abstract

ABSTRACTLiquid 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.