The effect of pressure on hydrogen bonding in water: IR study of νOD HDO at pressures of up to 1500 bar

A seeming contradiction has been revealed between the behaviour of the shortest intermolecular separation roo and that of the frequency of the OH vibration of H2O under compression in liquid water. Decrease of roo with increasing pressure up to 2 kbar seems to be evidence of strengthening of the hydrogen bonding, but the increase in the frequency of νOH H2O seems contradictory. To clear up this question, measurements of the integrated intensity of IR absorption for νOD HDO have been made which definitely show that the energy of the hydrogen bonds decreases under compression at least up to 1.5 kbar. The decrease in the intensity is of about 20%, i.e., essentially more than the estimated accuracy of the measurements. Monte Carlo simulations of the compression of liquid water show that the behaviour of rOO, νOH, and the integrated intensity can be explained by the bending of hydrogen bonds.