FREQUENCIES OF H-O-H, H-O-D AND D-O-D BENDING FUNDAMENTALS IN LIQUID WATER

The bending fundamentals ν2 of the three isotopic species of water, H2O, D2O and HDO, were examined in the infrared spectra of liquid water at 0–99.9% D. The peak positions of the three bands vary linearly with the molar fractions of the three isotopic species. The half‐widths of ν2 of H2O surrounded by D2O and of D2O surrounded by H2O, which are largely free from vibrational coupling, have been whown to reflect the distrbution of instantaneous hydrogen‐bond strengths in liquid water. The contribution to the ν2 band width from dynamic processes is relatively small. Vibrational coupling, in the spectra of isotopically pure H2O or D2O, leads to additional broadening and to a sizable shift of the band center to lower frequencies. Small band shifts confirm that weak vibrational coupling also occurs between HDO and H2O and H2O and between HDO and D2O. Copyright © 1990 John Wiley & Sons, Ltd.