Abstract
Complex χ(2) spectra of buried silica/isotopically diluted water (HOD-D2O) interfaces were measured using multiplex heterodyne-detected vibrational sum frequency generation spectroscopy to elucidate the hydrogen bond structure and up/down orientation of water at the silica/water interface at different pHs. The data show that vibrational coupling (inter- and/or intramolecular coupling) plays a significant role in determining the χ(2) spectral feature of silica/H2O interfaces and indicate that the doublet feature in the H2O spectra does not represent two distinct water structures (i.e., the ice- and liquid-like structures) at the silica/water interface. The observed pH dependence of the imaginary χ(2) spectra is explained by (1) H-up oriented water donating a hydrogen bond to the oxygen atom of silanolate, which is accompanied by H-up water oriented by the electric field created by the negative charge of silanolate, (2) H-up oriented water which donates a hydrogen bond to the neutral silanol oxygen, and (3)...
Published Version
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