The center frequencies of Peak I are close in frequency to the intermolecular bending vibration mode of liquid water. Since this vibration is Raman active, the bands are mainly observed by Raman and hyper Raman spectroscopy. The center band position is 1.62 THz (H2O) and 1.56 THz (D2O), respectively. In the THz absorption spectra of the liquid water, the band intensity is Both in the Raman and THz spectroscopy, the center frequency of H2O is higher than that of D2O.