Four-photon Rayleigh-wing spectroscopy of the aqueous solution of α-chymotrypsin protein

The spectra of coherent librations of H₂O molecules, coinciding in frequencies with the rotational spectrum of gaseous H₂O, are observed for the first time in aqueous solutions of α-chymotrypsin protein and hydrogen peroxide and in deionised Milli-Q water by the method of four-photon laser scattering in the frequency range 0–100 cm^-1. The resonance contribution of molecular librations to the four-photon scattering signal considerably increases in aqueous solutions compared to water. The resonances related to the lines of the ortho- and para-modifications of the natural isotope of the H₂O molecule in the gas phase are recorded in the four-photon scattering spectra. It is found that the protein molecule in aqueous solution selectively interacts with the para-H₂O, which makes it possible to interpret some features of the interaction of microwave radiation with biological objects and to develop a new class of laser biotechnologies.