Hydrogen Bond Relaxation Dynamics In Acid,base,and Salt Solutions

Acid,alkali and salt solutions play a highly important role in the fields of biology,medicine,agriculture,environmental protection and so on.Hydration is a very common but important chemical process.Scientists have made persistent efforts to understand ionic hydration,but their understanding of many aspects needs to be clearly unified.In this paper,from the perspective of solute charge injection-induced hydrogen bond cooperative relaxation,density functional theory?DFT?calculation was used to study solute ions induced relaxation dynamic process in acid,alkali and salt solutions,and the theoretical model of solute-solvent interaction in solutions were proposed.The polarization of solute ions on local O:H—O hydrogen bonds were clarified.To some extent,it has been verified that the hydration reaction modulates the hydrogen bonding network and relaxation behavior of solutions and confirms the physical mechanism of physical and chemical performance of solutions by means of charge injection into the solvent.The main research contents and results of this paper are as follows:?1??Li,Na,K?OH solvation generates Y⁺alkali metal ion and hydroxyl OH^-.DFT calculation reveals that the Y⁺cation locates eccentrically at the interstitial hollow site of?2a?3 ice cubic to form Y⁺·4H₂O unit,whereas OH^-replaces central H₂O of the tetrahedron to form a OH^-·4H₂O unit.The Y⁺interacts with the surrounding four oriented H₂O molecules through Y⁺???H⁺Coulomb repulsion and Y⁺:O^2-Coulomb attraction.The lone pair ":" converts one O:H—O bond to the O:???:O super hydrogen bond by turning the H₂O·4H₂O into OH^-·4H₂O.The Y⁺???H⁺repulsion increases each other' spacing,and the Y⁺:O^2-attraction decreases it,which shows the anisotropic polarization of Y⁺alkali metal ions.The anisotropic polarizability of Y⁺,the O:???:O compression and the H—O bond contraction of the solute OH^-distort the solute bonding network together,and cause the blue shift and red shift of O:H—O segmental phonon frequency,as confirmed spectroscopically.?2?H?Cl,Br,I?acid solvation generates X-halogen ion and hydronium H₃O⁺.DFT calculation reveals that the X-anion locates eccentrically at the interstitial hollow site of?2a?3 ice cubic to form X-·4H₂O unit,whereas H₃O⁺replaces the central H₂O of the tetrahedron to form H₃O⁺·4H₂O.X-anion interacts with the surrounding four oriented H₂O molecules through X-???O^2-Coulomb repulsion and X-:H⁺Coulomb attraction.An additional H⁺proton transits one O:H—O bond to the H???H anti-hydrogen through converting the H₂O·4H₂O unit to H₃O⁺·4H₂O.H⁺???H⁺repulsion destroys the hydrogen bond network in the acid solution.The X-???O^2-repulsion increases itself and makes H₂O into an undercoordination state.The X-:H⁺attraction reduces its distance and forms an X:H—O bond,causing the undercoordination of neighboring H₂O.This reveals the strong anisotropic polarization of X-halide ions.The anisotropic polarizability of the solute X-and the H???H quantum fragilization destroy the network in the acid solution,leading to the blue shift and red shift of phonon frequency of O:H—O segment,which is confirmed by the experimental DPS.?3??Mg,Ca,Sr??Cl,Br?₂ solvation generates Y²⁺divalent cation and X-halogen ion.DFT calculation reveals that the Y²⁺cation locates eccentrically at the interstitial hollow site of?2a?3 ice cubic to form Y²⁺·4H₂O unit,and the X-anion locates eccentrically at the interstitial hollow site of?2a?3 ice cubic to form X--4H₂O unit.Y²⁺cation interacts with H₂O molecules in the first hydration shell through U²⁺???H⁺Coulomb repulsion and Y²⁺:O^2-Coulomb attraction.X-anion interacts with the surrounding four oriented H₂O molecules through X-???O^2-Coulomb repulsion and X-:H⁺Coulomb attraction.Solute Y²⁺and X-both show the anisotropic polarization.The anisotropic polarization capabilities of Y²⁺and X-distort the hydrogen bond network of the salt aqueous solution,which causes the blue shift and red shift of phonon frequency of O:H—O segment,which was also confirmed by experimental DPS.