Water: Hydrogen bonding and vibrational spectroscopy, in the bulk liquid and at the liquid/vapor interface

Vibrational spectroscopy, including infrared, Raman, sum-frequency, and ultrafast, has proven to be an exceptionally useful technique for probing the structure and dynamics of water, in the bulk liquid, and at the liquid/vapor interface. Focusing on the case of dilute HOD in D2O, we have previously analyzed infrared and Raman spectra for the bulk liquid by considering the OH frequency distribution for the ensemble of HOD molecules, and its partitioning into sub-distributions for molecules in different hydrogen-bonding environments, using one particular hydrogen-bonding definition. We have similarly analyzed the sum-frequency spectrum for the liquid/vapor interface by considering the relevant spectral density and its partitions. We show that our conclusions about the molecular origins of spectral features, and the lack of correlation in the hydrogen-bonding region between frequency and hydrogen-bonding environment, are robust, in the sense that qualitatively similar results are obtained for five other, not necessarily closely related, hydrogen-bond definitions.