Raman Investigation of Proton Hydration and Structure in Concentrated Aqueous Hydrochloric Acid Solutions

Walrafen, G. E.; Chu, Y. C.; Carlon, Hugh R.

doi:10.1007/978-1-4615-3444-0_26

Cited by 7 publications

(15 citation statements)

References 4 publications

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“…The prominent Raman band at very low frequencies (below 200 cm −1 ) in Figure 2a−c has previously been attributed to the "anisotropic proton polarizability of the hydrogen bonds in H 5 O 2 + groupings". 19 However, our results shown in Figure 2c, as well as those of previous studies, 37,38 indicate that NaCl solutions also produced enhanced intensity in this region; thus, both the hydrated proton and its counterion contribute to low- frequency Raman scattering that is enhanced relative to pure water. With regard to the high-frequency OH stretch region (at ∼3300 ± 300 cm −1 ), our additional polarized Raman-MCR measurements reveal a rather abrupt increase in depolarization ratio above ∼3200 cm −1 (see Figure S8), indicating that the low-and high-frequency portions of the hydrated proton OH stretch band arise from structurally distinct configurations.…”

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confidence: 85%

Decomposition of the Experimental Raman and Infrared Spectra of Acidic Water into Proton, Special Pair, and Counterion Contributions

Daly

Streacker

Sun

et al. 2017

J. Phys. Chem. Lett.

141

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Textbooks describe excess protons in liquid water as hydronium (HO) ions, although their true structure remains lively debated. To address this question, we have combined Raman and infrared (IR) multivariate curve resolution spectroscopy with ab initio molecular dynamics and anharmonic vibrational spectroscopic calculations. Our results are used to resolve, for the first time, the vibrational spectra of hydrated protons and counterions and reveal that there is little ion-pairing below 2 M. Moreover, we find that isolated excess protons are strongly IR active and nearly Raman inactive (with vibrational frequencies of ∼1500 ± 500 cm), while flanking water OH vibrations are both IR and Raman active (with higher frequencies of ∼2500 ± 500 cm). The emerging picture is consistent with Georg Zundel's seminal work, as well as recent ultrafast dynamics studies, leading to the conclusion that protons in liquid water are primarily hydrated by two flanking water molecules, with a broad range of proton hydrogen bond lengths and asymmetries.

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confidence: 85%

Decomposition of the Experimental Raman and Infrared Spectra of Acidic Water into Proton, Special Pair, and Counterion Contributions

Daly

Streacker

Sun

et al. 2017

J. Phys. Chem. Lett.

141

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“…3 Accordingly, quantum mechanical proton tunneling is expected to occur in the two 0-H-0 bonds (Figure 1). 3 Accordingly, quantum mechanical proton tunneling is expected to occur in the two 0-H-0 bonds (Figure 1).…”

Section: Normal-coordinate Analysis Pad Interpretationmentioning

confidence: 99%

Low-frequency Raman spectra from concentrated aqueous hydrochloric acid: normal-coordinate analysis using a "four-atomic" model of Cs symmetry, (H2O)2(H3O+)(Cl-H2O)

Walrafen¹,

Chu²

1992

J. Phys. Chem.

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9127 (1 3) Girard, P.; Couffignal, R.; Kogan, H. B. Terruhedron Lerr. 1981,22, (14) Wolfe, S.; Pilgrim, W. R.; Garrard, T. F.; Chamberlain, P. Can. J. (15) Baranovic, G.; Colombo, L.; Furic, K.; Durig, J. R.; Sullivan, F.; (16) Hoshi, T.; Okubo, J.; Kobayashi, M.; Tanizaki J. Am. Chem. SOC. (17) Dale, W. J.; Starr, L.; Sterobel, C. W. J. Org. Chem. 1961, 2225. (18) Hashimoto, S.; Shimojima, A.; Yuzawa, T.; Hiura, H.; Abe, J.; (19) Kunimatsu, N.; Takahashi, H. To be published. (20) Colombo, L.; Kirin, D.; Volovsek, V.; Lindsay, N. E.; Sullivan, J. F.; 3959.Low-frequency, X ( Z 2 ) Y, X(ZX) Y, and isotropic, BoseEinstein corrected, Raman spectra were obtained from concentrated aqueous HCl. Normal-coordinate analysis of the intermolecular vibrational frequencies was carried-out with a "four-atomic" (H20)2(H30+)(CI-Hz0) model of C, symmetry using structural parameters obtained from X-ray RDF data. The C1-ion is directly hydrogen-bonded to one of the protons of H30+ in this structure, i.e., one C1-is interspersed between, and hydrogen-bonded to both, a proton of H30+ and an outer H20. The C, structure fits the Raman data when [H20 [HCI] RDF peaks' as the two 0 4 1 distances of the C, structure. These two 0-C1 distances and the 0-0 RDF distance of 2.52 A place the C1-above the three protons, Le., the line from the 0 of H30+ to C1-differs only =9O from the 3-foid axis of H30+. This C, model is analogous to that used by Gigu5re2 to explain the weakness of HF, but the hydrogen bonding between C1-and H30+ is much weaker than that between F and H30+, in accord with the greater acid strength of HCl. < 4, whereas H904+ fails to explain a key isotropic feature. The C, model also explains both of the 3.13-and 3.63-u X-ray I ,

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“…In an effort to explain these stoichiometric restrictions, a structure involving direct contact between H 3 O + and Cl - was postulated. , While the through-space interaction is electrostatically favorable, the suggested structure requires an extremely bent hydrogen bond. As we shall see, this structure is inconsistent with the X-ray and neutron diffraction data.…”

Section: Introductionmentioning

confidence: 99%

Structure of Concentrated HCl Solutions

Agmon

1998

J. Phys. Chem. A

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A pentagonal ring is suggested as the basic structural unit of HCl(H2O)6 and (HCl)2(H2O)6 in solution. Modeled after the X-ray structure of a caged H13O6 + compound, it contains bridged H5O2 + and Cl- ions, each with a coordination number around four. In the most concentrated HCl solutions, one of the ligands solvating Cl- is HCl, giving rise to a bichloride moiety. The proposed structure explains qualitatively the stoichiometry, ion mobility, (IR, Raman) spectroscopy and (X-ray, neutron) diffraction data of concentrated HCl solutions and provides a semiquantitative fit to the X-ray radial distribution function. The ring structure is a likely candidate for the structure of protonated HCl clusters in the gas phase and for the contact ion-pair formed following HCl dissociation in solution.

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Raman Investigation of Proton Hydration and Structure in Concentrated Aqueous Hydrochloric Acid Solutions

Cited by 7 publications

References 4 publications

Decomposition of the Experimental Raman and Infrared Spectra of Acidic Water into Proton, Special Pair, and Counterion Contributions

Decomposition of the Experimental Raman and Infrared Spectra of Acidic Water into Proton, Special Pair, and Counterion Contributions

Low-frequency Raman spectra from concentrated aqueous hydrochloric acid: normal-coordinate analysis using a "four-atomic" model of Cs symmetry, (H2O)2(H3O+)(Cl-H2O)

Structure of Concentrated HCl Solutions

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