CO2-ethanol interaction studied by vibrational spectroscopy in supercritical CO2

Infrared spectroscopic measurements of the nu(OD) stretching vibration of dilute deuterated ethanol in supercritical CO2 have been performed and analyzed, via a theoretical model and ab initio calculations, to better understand the ethanol-CO2 interaction. It was found that strongly attractive interactions, predominantly due to dispersion, dominate the stabilization energy between ethanol and CO2. Differences between the observed and theoretically predicted spectral shifts indicate the presence of local density enhancements. The continued observation of these enhancements up to temperatures significantly greater than the critical one, T/T-c greater than or equal to 1.3, suggests that ethanol is a strongly attractive solute for CO2, at least in the spatial vicinity of the OH functional group. This suggestion is also supported by an analysis of the local density enhancement factors, as extracted from IR and other spectroscopies, as well as by the ab initio calculations.