Size Dependence of Liquid-Liquid Phase Separation by in Situ Study of Flowing Submicron Aerosol Particles.

Liquid-liquid phase separation (LLPS) of atmospheric particles impacts a range of atmospheric processes. Driven by thermodynamics, LLPS occurs in mixed organic-inorganic particles when high inorganic salt concentrations exclude organic compounds, which develop into a separate phase. The effect of particle size on the thermodynamic and kinetic drivers of LLPS, however, remains incompletely understood. Here, the size dependence was studied for the separation relative humidity (SRH) of LLPS. Submicron organic-inorganic aerosol particles of ammonium sulfate mixed with 1,2,6-hexanetriol and polyethylene glycol (PEG) were studied. In a flow configuration, upstream size selection was coupled to a downstream fluorescence aerosol flow tube (F-AFT) at 293 ± 1 K. For both mixed particle types, the SRH values for submicron particle diameters of 260-410 nm agreed with previous measurements reported in the literature for supermicron particles. For smaller particles, the SRH values decreased by approximately 5% RH for diameters of 130-260 nm for PEG-sulfate particles and of 70-190 nm for hexanetriol-sulfate particles. From these observations, the nucleation rate in the hexanetriol-sulfate system was constrained, implying an activation barrier to nucleation of +1.4 to +2.0 × 10-19 J at 70% RH and 293 K. Quantifying the activation barrier is an approach for predicting size-dependent LLPS in the atmosphere.

Crystal structure of a tri-fluoro-methyl benzoato quadruple-bonded dimolybdenum complex.

The study of quadruple bonds between transition metals, in particular those of dimolybdenum, has revealed much about the two-electron bond. The solid-state structure of the quadruple-bonded dimolybdenum(II) complex tetra-kis-[µ-4-(tri-fluoro-methyl)-benzoato-κ2 O:O']bis[(tetra-hydro-furan-κO)molybdenum(II)] 0.762-pentane 0.238-tetra-hydro-furan solvate, [Mo2(p-O2CC6H4CF3)4·2THF]·0.762C5H12·0.238C4H8O or [Mo2(C8H4F3O2)4(C4H8O)2]·0.762C5H12·0.238C4H8O is reported. The complex crystallizes within a triclinic cell and low symmetry (P ) results from the inter-calated penta-ne/THF solvent mol-ecules. The paddlewheel structure at 100 K has inversion symmetry and comprises four bridging carboxyl-ate ligands encases the Mo2(II,II) core that is characterized by two axially coordinated THF mol-ecules and an Mo-Mo distance of 2.1098 (7) Å.