Solvation of benzene and phenyl halides in supercritical CO 2 studied by the interaction-induced CO 2 bending Raman band

Abstract

To study solvation in supercritical (SC) CO 2, Raman spectra of SC CO 2 and its solutions with benzene or phenyl halides were studied based on the CO 2 bending vibrations, which become weakly Raman active upon interaction between CO 2 and other molecules. The bending band was as broad as 87 cm − 1 in neat SC CO 2 at 15 MPa. The addition of solute molecules resulted in steep decreases in band wavenumber and width in the region of solute molar fraction x < 0.03, and in an almost linear increase in intensity up to x of about 0.1. Solvation of the aromatic molecules in SC CO 2 was discussed based on preliminary ab initio calculations, which suggested that the CO 2 molecule interacts more strongly with the solute π-electrons than with the halogen substituent.