The breakdown of the chiral SFG signal of individual water molecules into symmetric and asymmetric components implies that one needs to derive a new functional form to fit the heterodyne chiral SFG spectra of water. This will allow for extracting information about the underlying frequency distribution that can reveal molecular interactions of water. The functional form for a pair of water O-H stretching peaks should contain a pair of opposite Lorentzian curves with equal amplitude and a frequency displacement, as in (15) where ω is the IR frequency, A is the amplitude of the pair, is the frequency of the midpoint between the two Lorentzian curves, is the difference in frequency between the two Lorentzian curves, and relates to the peak width. This functional form involves fewer free parameters in fitting the chiral SFG spectra of water, as fitting two Lorentzian curves requires six parameters (two amplitudes, two widths, and two centers) whereas the new functional form requires only four (one amplitude, one width, center frequency, and a frequency difference). Fitting to a pair of opposite curves yields one center frequency instead of two, thus producing a single peak in the frequency distribution, which is consistent with the IR spectrum of first hydration shell water (Figure ).