Study Of Effect Of Isotopic Substitution On Hydrogen Bond Structure Of Water System By Raman Spectrum

Water is the source of life,and it is important to study its nature and structure.Researchers have used a large number of experimental methods and theoretical models to carry out multi-angle research on water,and the results obtained are increasing day by day.The hydrogen bond network of the water system plays an important role in the physical and chemical properties of water molecules,because of the sensitivity of Raman spectroscopy to the local environment of water molecules,it can reflect the important information of the hydrogen bond structure change through the change of molecular stretching band.After the emergence of stimulated Raman scattering,a breakthrough progress has been made.We used spontaneous Raman scattering,stimulated Raman scattering combined with laser-induced breakdown to study isotopic substitution solutions of water and heavy water mixed in different volume ratios,and analyzed the effects of isotopic substitution on water and heavy water under normal and extreme conditions.Research shows:1.First,the spontaneous Raman scattering spectra of mixed solutions with different volume ratios of heavy water in water were measured,and a five-component model was used for Gaussian peak fitting of the obtained spectra.The five components represent ice-like tetrahedron hydrogen bond structure,tetrahedron hydrogen bond structure in water,single-donor hydrogen bond structure,single hydrogen bond structure,and non-hydrogen bond structure.After the increase of the isotopic substitution ratio of water,the Raman peak representing the tetrahedron hydrogen bond structure of ice is continuously shifted from 3043 cm^-1 to 3099 cm^-1,the Raman peak corresponding to the tetrahedral hydrogen bond structure in water only shifted from 3235 cm^-1 to 3275 cm^-1 at the first time of isotopic substitution,and then remained unchanged.The Raman peaks corresponding to the single-donor hydrogen bond structure,the single hydrogen-bonded structure and the non-hydrogen-bonded structure do not undergo frequency shift.We believe that isotopic substitution only affects the tetrahedral hydrogen bond structure.Then,the same experimental operation was performed on heavy water,and the results obtained were consistent with water,which further verified the correctness of our opinion.2.Second,a laser with an energy of 45 mJ,a wavelength of 355 nm,and a pulse width of 6 ns was used to excite the mixed solution of water and heavy water with different volume ratios to obtain its forward stimulated Raman scattering spectrum.After the intense laser light is incident,it will not only act as excitation light,but also cause laser-induced breakdown of the sample,generating laser-induced plasma and excessive electrons,the plasma diffuses to form a shockwave and compresses the liquid,creating an extreme environment,it makes anomalous Raman peaks that cannot be generated under ordinary circumstances appear in the stimulated Raman scattering spectrum.Under this condition,the isotopic substitution only affects the tetrahedral hydrogen bond structure,which is consistent with the conclusion obtained by spontaneous Raman scattering,but the changes of the hydrogen bond structure of water and heavy water caused by isotopic substitution are not exactly the same:For water,isotopic substitution promote the transition of its hydrogen bond structure from a tetrahedral structure to a non-tetrahedral structure;but for heavy water,isotopic substitution promote its transition from a tetrahedral structure to a non-hydrogen bond structure.In addition,the isotopic substitution will also change the way water molecular and electrons are combined,and promote the binding from strong to weak.