Four-photon polarization spectroscopy of the rotational resonances in liquids in the range 0–3 THz

The spectra of the coherent molecular rotation that coincide with the rotational spectra of the corresponding molecules in the gas phase are measured for the first time using four-photon coherent laser spectroscopy in the range 0–100 cm^?1 in several liquids (CCl₄, H₂O₂, D₂O, and H₂O). The measured spectra make it possible to separate the spectral contributions of the slow rotational molecular motions about the equilibrium and the fast rotations. The selectivity of the action of the microwave radiation on biological objects can be increased using the results obtained.