Four-photon laser spectroscopy of liquid water and aqueous solutions of α-chymotrypsin in the range ±5 cm−1

The resonances located at 1.2, 1.6, 2.0, and 2.3 cm−1 with a width of ∼0.2 cm−1 were observed for the first time in the range ±5 cm−1 of the four-photon Rayleigh wing spectra of distilled water and aqueous solutions of the protein α-chymotrypsin. The line at 2.3 cm−1 belongs to the rotational transition 3(2, 1)–4(1, 4) of the ground vibrational state of water. In the presence of the protein, the spectrum is modified by the appearance of new lines, located at 0.74, 2.8, and 3.2 cm−1. The modification of the spectrum observed is interpreted as a manifestation of low-frequency vibrations of large molecular fragments in aqueous protein solutions and as a result of the structuring of water in the vicinity of protein molecules.