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We resolved the O:H-O bond transition from the mode of ordinary water to its hydration in terms of its phonon stiffness (vibration frequency shift Δω), order of fluctuation (line width), and number fraction (phonon abundance), fx(C) = Nhyd/Ntotal. The fx(C) follows fH(C) = 0, fLi(C) ∝ fOH(C) ∝ C, and fBr(C) ∝ 1 - exp(-C/C0) toward saturation with C being the solute concentration. The invariant dfx(C)/dC suggests that the solute forms a constantly sized hydration droplet without responding to interference of other ions because its hydrating H2O dipoles fully screen its electric field. However, the number inadequacy of the highly ordered hydration H2O dipoles partially screens the large Br-. The Br- then interacts repulsively with other Br- anions, which weakens its electric field and the fBr(C) approaches saturation at higher solute concentration. The consistency in the concentration trend of the fLiBr(C), the Jones-Dole viscosity η(C), and the surface stress of LiBr solution clarifies their common origin of ionic polarization. The resultant energy of the solvent H-O exothermic elongation by O: ⇔ :O repulsion and the solute H-O endothermic contraction by bond-order deficiency heats up the LiOH solution. An estimation of at least 0.15 eV (160% of the O:H cohesive energy of 0.1 eV) suggests that the H-O elongation is the main source heating up the solution, while the molecular motion, structure fluctuation, or even evaporation dissipates energy caped at 0.1 eV. [ABSTRACT FROM AUTHOR]

It has long been puzzling regarding the atomistic origin of the pressure-induced Raman optical phonon stiffening that generally follows a polynomial expression with coefficients needing physical indication. Here, we show that an extension of the bond−order−length−strength correlation mechanism and a local bond average approach to the pressure domain have led to an analytical solution to connect the pressure-induced Raman optical phonon stiffening directly to the bonding identities of the specimen and the response of the bonding identities to the applied stimulus. It is found that the pressure-induced blue-shift of Raman optical phonons arises from the bond compression and energy storage exerted by the compressive stress. Agreement between predictions and experimental measurements lead to the clarification of the detailed form for the polynomial coefficients, which provide an atomistic understanding of the physical mechanism of the external pressure induced energy gain, thermally induced bond expansion, as well as means of determining the mode atomic cohesive energy in a specimen. [ABSTRACT FROM AUTHOR]

An approach of local bond average (LBA) has been developed by extending the bond-order-length-strength correlation (Sun, C. Q. Prog. Solid State Chem.2007, 35, 1− 159) to temperature domain for the mechanism of the thermally driven bond expansion in a solid specimen. It is shown that the detectable quantities of a solid can be connected directly to the bonding identities and the response of the bonding identities to the stimulus of temperature change, being free from using the concepts in classical thermodynamics or hypothetical constants. The success of the LBA approach has been evidenced by fitting the observations from a number of specimens with derived information of atomic cohesive energy, which may go beyond the currently available approaches. [ABSTRACT FROM AUTHOR]

It has long been puzzling that water nanodroplets undergo simultaneously "supercooling" at freezing and "superheating" at melting. Recent progress (Sun et al. J. Phys. Chem. Lett.2013, 4, 2565, 3238) enables us to resolve this anomaly from the perspective of hydrogen bond (O:H-O) specific heat disparity. A superposition of the specific heat ?x(T) curves for the H-O bond (x = H) and the O:H nonbond (x = L) defines two intersecting temperatures that form the ice/quasi-solid/liquid phase boundaries. Molecular undercoordination (with fewer than four nearest neighbors in the bulk) stretches the ?H(T) curve by raising the Debye temperature TDH through H-O bond shortening and phonon stiffening. The ?H(T) stretching is coupled with the ?L(T) depressing because of the Coulomb repulsion between electron pairs on oxygen ions. The extent of dispersion varies with the size of a droplet that prefers a core-shell structure configuration?the bulk interior and the skin. Understandings may open an effective way of dealing with the thermodynamic behavior of water droplets and bubbles from the perspective of O:H-O bond cooperativity. [ABSTRACT FROM AUTHOR]

A combination of the Lagrangian mechanicsof oscillators vibration,molecular dynamics decomposition of volume evolution, and Raman spectroscopyof phonon relaxation has enabled us to resolve the asymmetric, local,and short-range potentials pertaining to the hydrogen bond (O:H–O)in compressed ice. Results show that both oxygen atoms in the O:H–Obond shift initially outwardly with respect to the coordination origin(H), lengthening the O–O distance by 0.0136 nm from 0.2597to 0.2733 nm by Coulomb repulsion between electron pairs on adjacentoxygen atoms. Both oxygen atoms then move toward right along the O:H–Obond by different amounts upon being compressed, approaching identicallength of 0.11 nm. The van der Waals potential VL(r) for the O:H noncovalent bond reachesa valley at −0.25 eV, and the lowest exchange VH(r) for the H–O polar-covalentbond is valued at −3.97 eV. [ABSTRACT FROM AUTHOR]