High-pressure and concentration-dependent studies on C-H---O interactions of binary aqueous mixtures:: Formic acid/D2O and acetone/D2O

The C-H---O interactions of formic acid and acetone aqueous solutions were studied under various concentrations. The infrared spectra of acetone/D2O were also measured as a function of pressure. The C-H stretching frequency of formic acid reveals a red-shift with dilution. On the other hand, upon diluting acetone with D2O, the blue-shift with dilution in C-H stretching frequency was observed. Further high-pressure study provides the experimental evidence for the enhancement of hydrophobic hydration as the sample was compressed to high-pressure ices, while C-H vibration of acetone, being transformed from liquid to high-pressure ice VII, are altered into a band located at similar to 2950 cm(-1). The C-H---O interaction may be a distinct possibility to understand the band-shape and frequency-shift of the C-H stretching modes of formic acid/D2O and acetone/D2O.