Fig. 2: The effect of hydrogen bond vibrations on the dielectric susceptibility anisotropy.

The direction of the hydrogen bond is defined as the parallel direction. (I) In this hydrogen bond unit, if only the bending mode is considered, then the dielectric susceptibility anisotropy is negative (χ_|| < χ_⊥) because the dielectric susceptibility in the vertical direction (χ_⊥) is disturbed. (II) In contrast, if only the stretching mode is considered, then the dielectric susceptibility in the parallel direction (χ_||) is disturbed. As a result, a linearly polarized probe pulse (E_p) traversing liquid water could acquire ellipticity with opposite handedness because of the two types of molecular motions. A bipolar TKE response combining these two influences is expected