In situ Investigation of Carboxylate Adsorption at the Fluorite/Water Interface by Sum Frequency Spectroscopy

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This work presents a study of carboxylate adsorption at the fluorite/water interface by vibrational sum frequency spectroscopy. A homologous series of monocarboxylic ions including formate, acetate, propionate, hexanoate, and dodecanoate was studied in frequency regions corresponding to the νCH and νCO/δCH response. Previously reported vibrational and Raman modes were investigated for their sum frequency activity. For a more reliable band assignment, sum frequency measurements on systematically deuterated compounds were completed and compared with calculated band positions and intensities. Different polarization configurations were utilized, together with symmetry properties of bands derived from a normal-mode analysis, to classify the observed fundamentals and overtones. Differences in chain length led to striking changes in the spectral signatures of the compounds studied and were related to the molecular structure of the adsorbates and interfacial water molecules.