Structure and Dynamics of Concentrated Hydrochloric Acid Solutions

Abstract

Self-consistent iterative multistate empirical valence bond (SCI-MS-EVB) simulations for four different concentrated hydrochloric acid (HCl) concentrations (0.43, 0.85, 1.68, and 3.26 M) were conducted to study the structure and dynamic properties of the aqueous multiple excess proton systems. The present, more extensive simulations, confirm that the hydrated excess protons have a tendency to form metastable contact ion pairs by positioning the hydronium oxygen lone pair sides toward one another, in agreement with earlier work [ Wang, F. Izvekov, S. Voth, G. A. J. Am. Chem. Soc. 2008 , 130 , 3120 ]. This unusual behavior results from the special "amphiphilic" nature of the hydrated excess proton. Increasing the acid concentration to 3.26 M was found to have minor effects on the solvation structures of the hydrated proton and chloride counterion, while the average lifetime of the hydrated proton contact ion pairs was reduced. The addition of salts (KCl and NaCl) into the acid solution increases the stability of the hydrated proton pairs and reduces the proton diffusion.

A THz/FTIR fingerprint of the solvated proton: evidence for Eigen structure and Zundel dynamics

“…This is in agreement with theoretical predictions. 31,32 For the solvated proton H pair + and its interaction with hydration water, our data are consistent with a model where the unperturbed center frequenciesñ 0 (see Tables 1 and 2) of the damped harmonic oscillator resonances remain unchanged while the linewidths decrease. We conclude that the local structure is still intact while the distribution of the thermal bath states is assumed to be affectd leading to increased relaxation times t.…”

“…19 Simulations of aqueous acidic solutions are less abundant. 23,30,31,32 While some of these investigations predict contact or solvent shared ion pairing between oppositely charged ions, 30,31 others find a tendency of metastable contact ion pairs of hydrated excess protons. 32 Experimental studies of the solvated proton have been carried out along two directions.…”

“…23,30,31,32 While some of these investigations predict contact or solvent shared ion pairing between oppositely charged ions, 30,31 others find a tendency of metastable contact ion pairs of hydrated excess protons. 32 Experimental studies of the solvated proton have been carried out along two directions. Gas phase infrared predissociation spectroscopic measurements of protonated water clusters 20,21,33,34 show spectra that depend heavily on the water cluster size indicating a strong size dependence of the local cage structure surrounding the solvated proton.…”

Correlated dynamics in aqueous proton diffusion

“…Additionally, the same type of correlation was found previously by Xu et al in their the self-consistent iterative multistate empirical valence bond simulations of HCl solutions. 51 …”

The Structure of (H3O)2B12F12·6H2O – a CCP Lattice of B12F122– Anions Intercalated with a Nonplanar Network of O–H···O Connected O6 Rings

“…The nature of hydronium ions (i) in bulk aqueous solutions, [19][20][21] (ii) on the surface of aqueous solutions (i.e. at the air/water interface, where H 3 O + ions may be concentrated relative to the bulk solution), [22,23] and (iii) as free H 3 O + ions [24] or as [(…”