Water–CO 2 interaction in supercritical CO 2 as studied by infrared spectroscopy and vibrational frequency shift calculations

Abstract

Infrared absorption measurements of diluted perdeuterated water in supercritical carbon dioxide are reported. The frequency shift of the anti-symmetric stretching mode ( ν 3) is analysed using an analytical molecular model to get insights into the water–CO 2 interaction. Attractive forces, namely, dispersive and dipole–quadrupole interactions, are found dominant in the stabilisation energy of the water–CO 2 pair. Differences between observed and calculated frequency shifts reveal local density enhancements (LDE). The observation of LDE at temperature greater than the critical one ( T/ T c ≥ 1.3) allows to conclude that water acts as an attractive solute in the hyper-compressible regime of the solvent.