Hydrogen bonds librational state

The mixed model of water comprising the librational (LIB) and vibrational (VTB) fractions will be used. We employ four molecular mechanisms a, b, c, and d. The first one, a, refers to the LIB state, in which a permanent dipole reorients in the hat potential formed by tom or weak hydrogen bonds (HB). The last three specific mechanisms (b, c, d), governed by vibrating hydrogen bonds, refer to the VIB state. 

Fig. 1.2 The experimentally determined spectral density of states of liquid water using the optical Kerr effect -linear response) is shown for comparison [3], Water is one of the most structured liquids in which there is large separation in timescales. The frequency range between 300 and 1,000 cm (1) is related to librational motions (note that the spectrum represented here is artificially truncated at 600 cm due to laser bandwidth hmitations), the peak at 170 cm (2) is hindered translational motion of the heavy O atoms, the 60 cm mode (3) is transverse or shear motion, and below 25 cm (4) corresponds to diffusive relaxation and hydrogen bond breaking [8]. The issue of inhomogeneous to homogeneous interpretations of the dynamic structure of liquid water still holds despite this additional structure. The agreement is quite good with the theoretical calculation of the corresponding spectral density of states for water but the calculations are rather insensitive to basis with respect to this observable. Reprinted with permission from [3]. Copyright 1994, American Chemical Society...

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