IN-SITU DETECTION OF ADSORBATES AT SILICA SOLUTION INTERFACES BY FOURIER-TRANSFORM INFRARED ATTENUATED TOTAL-REFLECTION SPECTROSCOPY USING A SILICA-COATED INTERNAL-REFLECTION ELEMENT/

A silica-coated ZnSe internal reflection element (IRE) was used to acq uire attenuated total reflection (ATR) Fourier transform infrared (FT- IR) spectra of ethyl acetate at an n-heptane/silica surface. A thin si lica film was deposited onto the IRE by withdrawing the substrate from a suspension of fumed silica; upon drying, a durable, porous SiO2 lay er is formed on the IRE that is stable in contact with aprotic solvent s. The layer thickness is targeted to be comparable to the depth of pe netration of infrared radiation beyond the IRE/film interface. These f ilms were used to investigate the adsorption of ethyl acetate onto sil ica from n-heptane. A multidimensional least-squares fit of the spectr oscopic data reveals multiple surface-site energies on the silica surf ace, as reflected in both the solution concentration dependence of eth yl acetate accumulation on the surface and the frequencies of vibratio nal modes that shift upon adsorption.