Charge-enhanced C-H-O interactions are investigated for imidazole hydrochloride/D2O mixtures. Based on the concentration-dependence results, the infrared spectra reveal a strong C-H band and a weak shoulder at similar to3065 cm(-1). The pressure-dependence measurements also exhibit considerable spectral changes as the mixtures transform to high-pressure ices. The absorption intensity of the weak shoulder, located in the region of 3060-3090 cm(-1), drastically increases as the pressure is elevated. Observation of this low frequency band provides the experimental evidence of C-2-H-O hydrogen bonds in the aqueous imidazolium solutions. Ab initio calculation results, predicting the frequency shift of the C-H stretching vibrations as C-H-O is interacting via hydrogen bonding, are discussed. Structural identification of the hydrophobic isomers in infrared spectra seems to be complicated by the presence of more than one stable isomeric form. (C) 2003 American Institute of Physics.