Optical absorption of fine gold particles in supercritical carbon dioxide for the characterization of solvent properties

The optical absorption of small gold particles was measured in supercritical carbon dioxide at different pressures up to 30 MPa and at 308 K. The absorption spectrum was found to depend significantly on pressure. The spectral peak position shifted to a longer wavelength and the peak width broadened with an increase in pressure. The pressure-dependence of the peak position was similar to that of a solvent parameter of E-T(30) obtained previously by a solvatochromic method. The optical absorption can be easily measured and it would be a helpful way for characterizing the nature of supercritical carbon dioxide. A model calculation indicated that the pressure-dependence of the peak position observed was qualitatively estimated by the change of dielectric constant of the carbon dioxide medium. It was suggested, however, that one should take account of other factors such as direct interactions between gold particles and the medium for quantitative explanation. (C) 1998 Elsevier Science B.V.