Raman spectroscopic and calculated vibrational wavenumbers of anion hydrates

Craig, J. D. C.

doi:10.1002/jrs.844

Cited by 10 publications

(7 citation statements)

References 12 publications

(12 reference statements)

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“…55 Likewise, Cl À in NH 4 Cl is characterized by a single band at B200 cm À1 with no discernible low-wavenumber band. 56 This assignment is qualitatively consistent with the theoretical THz spectra computed in the ionic limit (R 0 -0) with their maxima at approximately 80 cm À1 for Na + (aq.) and 200 cm À1 in the case of Cl À (aq.…”

supporting

confidence: 87%

Solvation shell resolved THz spectra of simple aqua ions – distinct distance- and frequency-dependent contributions of solvation shells

Śmiechowski

Sun

Forbert

et al. 2015

Phys. Chem. Chem. Phys.

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Hydration of ions is a topic of broad relevance in chemistry and biology. Liquid-state terahertz spectroscopy has been demonstrated to be able to detect even small solute-induced changes in the hydrogen bond network dynamics at the solute-water interface. Here, we apply ab initio molecular dynamics simulations to study the solvation of Na(+) and Cl(-) in bulk water in the context of their far-infrared responses. Spatial decomposition schemes for infrared spectra down to the THz regime reveal the importance of both dipolar couplings and correlations in particle motion in these aqueous solutions. The explicit representation of the electronic structure properly captures the solute-solvent polarization effects that are crucial for the interpretation of recent experimental data. This demonstrates that theoretical spectroscopy significantly complements experimental measurements and provides most detailed insights by selectively monitoring the spectral activity due to distinct hydration spheres.

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supporting

confidence: 87%

Solvation shell resolved THz spectra of simple aqua ions – distinct distance- and frequency-dependent contributions of solvation shells

Śmiechowski

Sun

Forbert

et al. 2015

Phys. Chem. Chem. Phys.

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“…This mode is assigned to the restricted stretch of the H-bond between water and CO 3 2-. 36 In K 2 CO 3 solutions in heavy water we found a broad mode at 209 cm À1 and assigned it to -C-OÁÁÁD-OD.…”

Section: Resultsmentioning

confidence: 80%

Vibrational Spectroscopic Studies and Density Functional Theory Calculations of Speciation in the CO₂—Water System

2006

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Raman spectra of CO(2) dissolved in water and heavy water were measured at 22 degrees C, and the Fermi doublet of CO(2), normally at 1285.45 and 1388.15 cm(-1) in the gaseous state, revealed differences in normal water and heavy water, although no symmetry lowering of the hydrated CO(2) could be detected. Raman spectra of crystalline KHCO(3) and KDCO(3) were measured at 22 degrees C and compared with the infrared data from the literature. In these solids, (H(D)CO(3))(2)(2-) dimers exist and the spectra reveal strong intramolecular coupling. The vibrational data of the dimer (C(2h) symmetry) were compared with the values from density functional theory (DFT) calculations and the agreement is fair. Careful measurements were made of the Raman spectra of aqueous KHCO(3), and KDCO(3) solutions in D(2)O down to 50 cm(-1) and, in some cases, down to very low concentrations (> or =0.0026 mol/kg). In order to complement the spectroscopic assignments, infrared solution spectra were also measured. The vibrational spectra of HCO(3)(-)(aq) and DCO(3)(-)(D(2)O) were assigned, and the measured data compared well with data derived from DFT calculations. The symmetry for HCO(3)(-)(aq) is C(1), while the gas-phase structure of HCO(3)(-) possesses Cs symmetry. No dimers could be found in aqueous solutions, but at the highest KHCO(3) concentration (3.270 mol/kg) intermolecular coupling between HCO(3)(-)(aq) anions could be detected. KHCO(3) solutions do not dissolve congruently, and with increasing concentrations of the salt increasing amounts of carbonate could be detected. Raman and infrared spectra of aqueous Na(2) -, K(2) -, and Cs(2)CO(3) solutions in water and heavy water were measured down to 50 cm(-1) and in some cases down to extremely low concentrations (0.002 mol/kg) and up to the saturation state. For carbonate in aqueous solution a symmetry breaking of the D(3h) symmetry could be detected similar to the situation in aqueous nitrate solutions. Strong hydration of carbonate in aqueous solution could be detected by Raman spectroscopy. The hydrogen bonds between carbonate in heavy water are stronger than the ones in normal water. In sodium and potassium carbonate solutions no contact ion pairs could be detected even up to the saturated solutions. However, solvent separated ion pairs were inferred in concentrated solutions in accordance with recent dielectric relaxation spectroscopy (DRS) measurements. Quantitative Raman measurements of the hydrolysis of carbonate in aqueous K(2)CO(3) solutions were carried out and the hydrolysis degree a was determined as a function of concentration at 22 degrees C. The second dissociation constant, pK(2), of the carbonic acid was determined to be equal to 10.38 at 22 degrees C.

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“…The simple diatomic model produces an upper limit for the force constants. A slightly more refined model is the central force method applied to a linear XYZ system, in which X = Cl − , Br − , or I − and Y and Z are H and O, respectively. , The required distances were: O−H bond 0.96 Å; the X − ···H distances were 2.18 Å for Cl − , 2.43 Å for Br − , and 2.61 Å for I − . , Apart from the H-bond frequency we wish to calculate, the model requires the O−H stretch frequency (3480 cm −1 ) and a frequency for the XYZ bend. It turns out that the latter has little influence on the final H-bond frequency, so it was assumed to be equal to the water librational frequency of 550 cm −1 .…”

Section: Resultsmentioning

confidence: 99%

Low-Frequency Modes of Aqueous Alkali Halide Solutions: An Ultrafast Optical Kerr Effect Study

2011

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A detailed picture of aqueous solvation of ions is central to the understanding of diverse phenomena in chemistry and biology. In this work, we report polarization resolved THz time domain measurements of the Raman spectral density of a wide range of aqueous salt solutions. In particular, the isotropic Raman spectral density reveals the frequency of the hydrogen bond formed between the halide ion and water. The frequency of this mode is measured for the series Cl(-), Br(-), and I(-) as a function of concentration, cation size, and charge. The frequencies extrapolated to zero concentration permit an estimation of the force constant of the mode, which is found to decrease with increasing halide mass and to be similar to the force constant associated with the water-water hydrogen bond. This result is consistent with recent calculations. The extrapolation of the frequency of the chloride hydrogen bond to zero concentration reveals a dependence of the frequency on the nature of the cation. This is ascribed to an interaction between the solvated anion and cation even at the lowest concentration studied here (<0.15 M). It is suggested that this behavior reflects the influence of the electric field of the cation on the hydrogen bond of an adjacent anion. Such interactions should be taken into account when modeling experimental data recorded at concentrations of ions in excess of 0.1 M. These measurements of the isotropic Raman spectral density are compared with those for the anisotropic response, which reflects the frequencies of the full range of hydrogen bonds in aqueous salt solutions. The anisotropic spectral density recovered can be modeled in terms of a concentration-dependent population of water-water H-bonds with a frequency unaffected by the ions, the halide-water hydrogen bonds, and a low-frequency collision-induced contribution.

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Raman spectroscopic and calculated vibrational wavenumbers of anion hydrates

Cited by 10 publications

References 12 publications

Solvation shell resolved THz spectra of simple aqua ions – distinct distance- and frequency-dependent contributions of solvation shells

Solvation shell resolved THz spectra of simple aqua ions – distinct distance- and frequency-dependent contributions of solvation shells

Vibrational Spectroscopic Studies and Density Functional Theory Calculations of Speciation in the CO₂—Water System

Low-Frequency Modes of Aqueous Alkali Halide Solutions: An Ultrafast Optical Kerr Effect Study

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Raman spectroscopic and calculated vibrational wavenumbers of anion hydrates

Cited by 10 publications

References 12 publications

Solvation shell resolved THz spectra of simple aqua ions – distinct distance- and frequency-dependent contributions of solvation shells

Solvation shell resolved THz spectra of simple aqua ions – distinct distance- and frequency-dependent contributions of solvation shells

Vibrational Spectroscopic Studies and Density Functional Theory Calculations of Speciation in the CO2—Water System

Low-Frequency Modes of Aqueous Alkali Halide Solutions: An Ultrafast Optical Kerr Effect Study

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Vibrational Spectroscopic Studies and Density Functional Theory Calculations of Speciation in the CO₂—Water System