Fraction and stiffness transition from the H[sbnd]O vibrational mode of ordinary water to the HI, NaI, and NaOH hydration states

Abstract

Solvation of acid, base, and salt is ubiquitously important to all subject areas in chemistry, health care and life science. However, fine resolution of the solvation dynamics, solute-solvent molecular interactions, and solute capability of transforming the hydrogen bond (O:HO, or HB) and surface stress remain great challenge. Incorporating the notion of O:HO bond cooperativity with a strategy of differential phonon spectroscopy (DPS) has enabled resolution on the fraction and stiffness of the solvent HB from the mode of water to the hydration shells upon NaOH, NaI and HI solvation. Results show that Na+ and I+ ionic polarization shortens the HO bond and stiffens its phonon from 3200 to 3500cm−1 in the hydration shells. The H+ in the HI solution forms a H↔H anti-HB that disrupts the solution network and surface stress. The excessive electron lone pairs of OH– form the O:⇔:O super-HB that compresses the network, sharing the same effect of mechanical compression shifting the HO phonon from above 3100cm−1 to its below; the solute HO bond performs the same to the HO dangling bond at surface featured at 3610cm−1. The fraction coefficients or phonon abundance transition, fH=0, fHO∝C, and fx∝1-exp(−C/C0) (x=Na+ and I− and C the solute concentration) towards saturation, feature the solute capability of HB transformation. Practice not only confirms the essentiality of the H↔H anti-HB point fragilization, the O:⇔:O super-HB point compression, and the ionic polarization to the performance of the respective HI, NaOH, and NaI solutions, but also demonstrate the power of the DPS that enables fine-resolution of solvation dynamics and solute capabilities.