Infrared optical constants of aqueous solutions of electrolytes. Acids and bases

Abstract

7) It appears from previous measurements that this orientational axis is identical with the longitudinal axis of inertia, however, we have not proved this generalization rigorously.(8) We are indebted to the referees for their comments on this matter. (9) Similar relations were derived by Norden [Chem. Script., 1, 145 (1971)] for the interpretation of the linear dichroic spectra of certain triarylmethane dyes. (10) The "in-plane" transitions are those polarized in the best plane of the molecule (which includes the twofold symmetry axis) whereasthe "out-of-plane" transitions are those polarized out of this plane.

H3O+ ions in aqueous acid solutions. The infrared spectra revisited

“…Furthermore, a frequency of 1730 cm-' is far too high for the bending mode of water molecules. As for the 1200 cm-"and, assignment to an overtone is ruled out by the following observations: ( a ) its intensity is too high, and it increases with decreasing water concentration; (b) its frequency at the maximum is often appreciably higher than twice the libration frequency of H 2 0 in acid sokutions (1,7). At any rate, the existence of discrete H502+ groups in aqueous acids now appears very d o~b t f u l in the light of recent findings, both theoretical and experimental.…”

The vibrational spectrum of the hydrated proton: Comparison of experiment, simulation, and normal mode analysis

“…[25][26][27][28]40 Falk and Giguere, 25 who measured the infrared transmission spectra of aqueous solutions of mineral acids, observed concentration-dependent absorption bands in three frequency regions, 1205, 1750, and 2900 cm Ϫ1 , with continuous absorption ranging from 1000 to 3500 cm Ϫ1 in the HCl solution/water difference spectrum. In their assignment of the absorption bands, based on the existence of the hydronium ion (H 3 O ϩ ), the first two bands were assigned as 2 symmetric bending and 4 asymmetric bending, respectively, while the other was assigned as 3 ϩ 1 stretching of the hydronium ion.…”

“…This is particularly true in the case of the excess proton in water: Although there have been numerous studies to measure the IR spectrum of hydrated protons in aqueous solutions, the spectra and the assignment of the absorption bands have been inconsistent. [25][26][27][28] Furthermore, the identity of the primary hydrated proton ''species'' in liquid water and the transient structures involved in the proton transfer process have been controversial issues. 6,29,30 The utility of vibrational spectroscopy for characterizing the hydrated proton hinges on the measurement of reliable infrared spectra and a firm basis for assigning the molecular motions contributing to the absorption bands.…”

Probing Small Protonated Water Clusters in Acetonitrile Solutions by 1H NMR

“…The Eigen cation has a C 3 symmetry about the central oxygen atom of a single H + 3 O cation (the Eigen core) while the Zundel cation has a C 2 symmetry about a central H + placed in between the oxygen atoms of two water molecules. These two limiting structural motifs of the solvated proton in water are continuously distorted to form less symmetrical structures by the continuously changing solvent environment which solvates them [67][68][69][70][71][72][73][74].…”