| Abstract
| - X-ray diffraction measurements for 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid ([BMIM][PF6])−CO2 systems were carried out at high pressures with a newly developed polymer cell. The intermoleculardistribution functions (ginter(r)) were obtained at 25 °C for neat [BMIM][PF6] and its solutions saturated withCO2 at 4 and 15 MPa, where the mole fractions (x) of CO2 correspond to 0.5 and 0.7, respectively. In ginter(r)for x = 0.5, two peaks appeared at around 2.8 and 3.2 Å. These two peaks in ginter(r) appreciably increasedfor x = 0.7; moreover, there was another peak observed at ∼3.8 Å. Only assuming the correlations betweenCO2 and [PF6]-, it is reasonably determined that the nearest-neighbor P([PF6]-)· · ·C(CO2) distances are 3.57and 3.59 Å with the coordination numbers being 1.8 and 4.0 for x = 0.5 and 0.7, respectively. It is concludedthat CO2 molecules are preferentially solvated to the [PF6]- anion.
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