Effect of hydrogen bonding on the direction of the dipole-moment derivative of the O–H bond in the water molecule

The ratio of the integrated absorption intensities of the ν3 and ν1 vibrations of H2O vapor is 20.6 [J. M. Flaud and C. Camy-Peyret, J. Mol. Spectrosc. 55, 278 (1975)] and so the dipole-moment derivatives for the stretching of the two bonds independently are 25.2° outside the bonds themselves. The corresponding ratio for the uncoupled D2O molecule isolated in H2O low-density ice I at∼100 K and zero pressure has been measured as 1.77 and 1.73, and for D2O isolated in the low-density H2O amorph as 1.90, 2.72, and 1.94 from the spectra of Devlin and his colleagues. The derivatives of the water molecule in ice are, therefore, directed along the bonds within the experimental uncertainty. The ratio of the integrated intensities of the ν3 and ν1 vibrations of H2O ice VIII at −10 °C and 32 kbar is 1.95 [D. D. Klug and Edward Whalley (in preparation)], which implies that the dipole-moment derivative is directed ∼2° outside the bond. This spectacular change of direction of the dipole-moment derivative on condensation is a newly recognized effect of hydrogen bonding.