Effects of equilibrium H-bond distance and angle changes on Raman intensities from water

The H-bond energy dispersion over the inhomogeneously broadened OD stretching contour from dilute HDO in H2O was determined from absolute Raman intensities; it displays a large minimum near omega=2440 cm(-1) from short, strong H bonds (in agreement with the peak omega from lda ice) and a large maximum near 2650-2675 cm(-1) due to extremely weak or broken H bonds (in agreement with the peak omega from dense, supercritical HDO in H2O, 0.9 g/cm3, 673 K). The difference between extrema is the maximum H-bond DeltaE, 5100+/-500 cal/mol, in excellent agreement with Pauling's limiting value. A pressure of 1500 bars yields an additional maximum and shoulder between the two dispersion extrema from pure water; saturated NaCl in water shows the additional maximum. The maxima near 3350 cm(-1) (1500 bar) or near 3360 cm(-1) (NaCl-H2O) arise from bent H bonds; 3350 cm(-1) (1500 bar) corresponding to an angle of approximate to170degrees in the joint frequency/bend, probability of Lawrence and Skinner [J. Chem. Phys. 118, 264 (2003)]. Rising omega refers to a higher probability of larger O-O distances, bent H bonds, and H-bond weakening and breakage. A approximate to50-80 cm(-1) difference between the 2727 cm(-1) OD peak from HDO in steam, and the 2650-2675 cm(-1) dispersion maximum is explained via the very broad approximate to60 cm(-1) liquid peak observed at 342 degreesC and 2000 bar. (C) 2004 American Institute of Physics.