Fermi Doublet Research Articles

Carbon Dioxide in 1-Butyl-3-methylimidazolium Acetate. I. Unusual Solubility Investigated by Raman Spectroscopy and DFT Calculations

The unusual solubility of carbon dioxide in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been studied by Raman spectroscopy and DFT calculations. It is shown that the solubility results from the existence of two distinct solvation regimes. In the first one (CO(2) mole fraction ≤ 0.35), the usual Fermi dyad is not observed, a fact never reported before for binary mixtures with organic liquids or ionic liquids (IL). Strong experimental evidence complemented by effective DFT modeling shows that this regime is dominated by a chemical reaction leading to the carboxylation of the imidazolium ring accompanied by acetic acid formation. The reactive scheme proposed involves two concerted mechanisms, which are a proton exchange process between the imidazolium cation and the acetate anion and the carboxylation process itself initiated from the formation of "transient" CO(2)-1-butyl-3-methylimidazole 2-ylidene carbene species. In that sense, CO(2) triggers the carboxylation reaction. Moreover, this dynamic picture circumvents consideration of a long-lived carbene formation in dense phase. The second regime is characterized by the detection of the CO(2) Fermi dyad showing that the carboxylation reaction has been strongly moderated. This finding has been interpreted as due to the interaction of the acetic acid molecules with the COO group of acetate anions involved in monodentate forms with the cation. The observation of the Fermi doublet allows us to infer that CO(2) essentially preserves its linear geometry and that the nature and strength of the interactions with its environment should be comparable to those existing in organic liquids and other IL as well. These results have been supported by DFT calculations showing that the CO(2) molecule interacts with energetically equivalent coexisting structures and that its geometry departs only slightly from the linearity. Finally, we find that the CO(2) solvation in Bmim Ac and 1-butyl-3-methylimidazolium trifluoroacetate (Bmim TFA) cannot be straightforwardly compared neither in the first regime due to the existence of a chemical reaction nor in the second regime because CO(2) interacts with a variety of environments not only consisting of ions pairs like in Bmim TFA but also with carboxylate and acetic acid molecule.

Preparation and Properties of a Monomeric High-Spin MnV–Oxo Complex

Oxomanganese(V) species have been implicated in a variety of biological and synthetic processes, including their role as a key reactive center within the oxygen-evolving complex in photosynthesis. Nearly all mononuclear Mn(V)-oxo complexes have tetragonal symmetry, producing low-spin species. A new high-spin Mn(V)-oxo complex that was prepared from a well-characterized oxomanganese(III) complex having trigonal symmetry is now reported. Oxidation experiments with [FeCp(2)](+) were monitored with optical and electron paramagnetic resonance (EPR) spectroscopies and support a high-spin oxomanganese(V) complex formulation. The parallel-mode EPR spectrum has a distinctive S = 1 signal at g = 4.01 with a six-line hyperfine pattern having A(z) = 113 MHz. The presence of an oxo ligand was supported by resonance Raman spectroscopy, which revealed O-isotope-sensitive peaks at 737 and 754 cm(-1) assigned as a Fermi doublet centered at 746 cm(-1)(Δ(18)O = 31 cm(-1)). Mn Kβ X-ray emission spectra showed Kβ' and Kβ(1,3) bands at 6475.92 and 6490.50 eV, respectively, which are characteristic of a high-spin Mn(V) center.

The effect of the Fermi resonance on the Raman scattering cross sections of the Fermi doublet ν1 and 2ν2 of liquid carbon disulfide in benzene

The effect of the Fermi resonance (FR) on the Raman scattering cross sections (RSCSs) of the Fermi doublet ν1, 2ν2 of liquid CS2 in C6H6 using the method of changing the volume concentration of the solution is investigated. We have calculated the RSCSs of the Fermi doublet ν1, 2ν2 using Onsager's theory with the 992cm−1 Raman line of C6H6 as the internal standard. The result shows that the RSCS of the ν1 line decreases with decreasing the volume concentration of CS2, while that of the 2ν2 line unexpectedly increases. With decreasing the volume concentration of CS2, two main effects of the solvent effect (SE) and the FR in binary solution that can make the ν1, 2ν2 RSCSs change: the SE, as calculated, reduces both the ν1 and 2ν2 RSCSs; the FR plays a significant role in reducing the ν1 RSCS and enhancing the 2ν2 RSCS. In comparison with our previous investigation [J. Raman Spectrosc. 41 (2010) 776–779], it was found that the stronger the FR is, the more the RSCS of the ν1 decreases and the 2ν2 increases. Thus, we proposed that the result can be best explained by taking into account the effect of the FR on the RSCSs of the Fermi doublet. In addition, this paper also gives an explanation to the experimental results deviating from the theoretical results of the scattering coefficients of CS2 in solvent C6H6 as mentioned in Fini's paper.

Preparation and characterisation of 2-formyl-1,4,5,6-tetrahydropyridine, a compound with a cracker-like odour

2-Acetyltetrahydropyridine is an important flavour constituent that imparts roasty, popcorn-like, and cracker-like odours to foods, such as bread, rice, popcorn, taco shells and tortilla chips. We postulated that the homologue with a formyl group in the C-2 position, 2-formyltetrahydropyridine, might have similar desirable odour qualities. Synthesis of this compound was performed by oxidation of 2-piperidinemethanol with silver carbonate supported on Celite®. This reaction produced a major volatile (46.9% of the total volatiles) with a retention index of 1023 on DB-1. GC–O revealed that the unknown had a strong cracker-like odour. The electron impact mass spectrum of the unknown had the following major ions: m/z 82, 111, 54, 68, 28, 43. The m/z 53–54 ratio and m/z 82–83 ratio were consistent with a 1,4,5,6-tetrahydropyridine ring structure. GC-FTIR of the unknown revealed an N–H stretching band at 3435cm−1 and a Fermi doublet at 2827 and 2713cm−1 that indicated the presence of an aldehyde. A strong carbonyl absorption band was present at 1703cm−1. The unknown was tentatively identified as 2-formyl-1,4,5,6-tetrahydropyridine, based on its retention index, odour quality, mass spectrum, and vapour phase infrared spectrum.

Pressure effect on the Fermi resonance doublets of ν1 ∼ ν12 and ν1+ν6 ∼ ν8 in pyridine

Raman spectra of pure pyridine, pyridine aqueous solution, and pyridine in methanol under high pressure were measured separately. Behaviors of two Fermi doublets, v1 and v12, v1+v6 and v8, occurred simultaneously in one pyridine molecule are analyzed according to their spectra, which indicates that the v1 Raman activity decreased with increasing pressure and disappeared eventually, which induced weakness and even disappearance of the Fermi resonance between v1 and v12, while the v1 Raman intensity variation had no effect on the presence of the Fermi resonance between v1+v6 and v8 as well as its variation law with increasing pressure. Those phenomena were interpreted by group theory in this article. It also indicates experimentally that all Raman bands of pyridine appeared blueshift with increasing pressure except that OH group appeared redshift. Moreover, frequency v1 shifted more quickly with increasing pressure than their counterparts did in neat liquid, so did its Raman intensity variation.

Broadening peculiarities of vibrational bands in the spectrum of carbon dioxide close to the critical temperature

Carbon dioxide Fermi doublet 1388/1285 cm−1Q-band broadenings and shifts measured using coherent anti-Stokes Raman spectroscopy are presented. Measurements were performed over a wide density range (0.1ρc < ρ < 1.9ρc) during compression in the gaseous and condensed states at temperatures close to critical (the reduced temperature values were Tr = 0.995, 1.000, and 1.006). At densities above the ρc critical value, the width of Q-bands did not increase as the density grew, and the low-frequency Q band considerably narrowed up to the density value 1.7ρc. The main reason for this anomalous behavior was progressing narrowing of the spectral contribution caused by the special features of rotational exchange in the condensed state and not related directly to the closeness to the critical point. The refined critical broadening value was about 10% of the width for the high-frequency Q-band and 15% of the width for the low-frequency Q-band.

Analysis of Measured and Calculated Raman Spectra of Indole, 3-Methylindole, and Tryptophan on the Basis of Observed and Predicted Isotope Shifts

The aromatic amino acid tryptophan plays an important role in protein electron-transfer and in enzyme catalysis. Tryptophan is also used as a probe of its local protein environment and of dynamic changes in this environment. Raman spectroscopy of tryptophan has been an important tool to monitor tryptophan, its radicals, and its protein environment. The proper interpretation of the Raman spectra requires not only the correct assignment of Raman bands to vibrational normal modes but also the correct identification of the Raman bands in the spectrum. A significant amount of experimental and computational work has been devoted to this problem, but inconsistencies still persist. In this work, the Raman spectra of indole, 3-methylindole (3MI), tryptophan, and several of their isotopomers have been measured to determine the isotope shifts of the Raman bands. Density functional theory calculations with the B3LYP functional and the 6-311+G(d,p) basis set have been performed on indole, 3MI, 3-ethylindole (3EI), and several of their isotopomers to predict isotope shifts of the vibrational normal modes. Comparison of the observed and predicted isotope shifts results in a consistent assignment of Raman bands to vibrational normal modes that can be used for both assignment and identification of the Raman bands. For correct assignments, it is important to determine force field scaling factors for each molecule separately, and scaling factors of 0.9824, 0.9843, and 0.9857 are determined for indole, 3MI, and 3EI, respectively. It is also important to use more than one parameter to assign vibrational normal modes to Raman bands, for example, the inclusion of isotope shifts other than those obtained from H/D-exchange. Finally, the results indicate that the Fermi doublet of indole may consist of just two fundamentals, whereas one fundamental and one combination band are identified for the Fermi resonance that gives rise to the doublet in 3MI and tryptophan.

First-principles calculations on anharmonic vibrational frequencies of polyethylene and polyacetylene in the Γ approximation

The frequencies of the infrared- and/or Raman-active (k=0) vibrations of polyethylene and polyacetylene are computed by taking account of the anharmonicity in the potential energy surfaces (PESs) and the resulting phonon-phonon couplings explicitly. The electronic part of the calculations is based on Gaussian-basis-set crystalline orbital theory at the Hartree-Fock and second-order Møller-Plesset (MP2) perturbation levels, providing one-, two-, and/or three-dimensional slices of the PES (namely, using the so-called n-mode coupling approximation with n=3), which are in turn expanded in the fourth-order Taylor series with respect to the normal coordinates. The vibrational part uses the vibrational self-consistent field, vibrational MP2, and vibrational truncated configuration-interaction (VCI) methods within the Gamma approximation, which amounts to including only k=0 phonons. It is shown that accounting for both electron correlation and anharmonicity is essential in achieving good agreement (the mean and maximum absolute deviations less than 50 and 90 cm(-1), respectively, for polyethylene and polyacetylene) between computed and observed frequencies. The corresponding values for the calculations including only one of such effects are in excess of 120 and 300 cm(-1), respectively. The VCI calculations also reproduce semiquantitatively the frequency separation and intensity ratio of the Fermi doublet involving the nu(2)(0) fundamental and nu(8)(pi) first overtone in polyethylene.

Study of asymmetric wavenumber shift of the Fermi doublet ν1 − 2ν2 in the Raman spectrum of liquid carbon disulfide

AbstractThe Raman spectra of liquid carbon disulfide (CS2) diluted with benzene (C6H6) have been measured. By changing the CS2, the concentration, we found an asymmetric wavenumber shift phenomenon. With decreasing concentration of CS2, the position of the ν1 (655 cm−1) band remains practically unchanged, and the 2ν2 (796 cm−1) band shifts toward higher wavenumbers. To interpret this asymmetric wavenumber shift phenomenon of the Fermi doublet ν1 − 2ν2 in the Raman spectra satisfactorily, we propose a modified Bertran model. The values of the Fermi resonance (FR) parameters of CS2 at different concentrations were calculated using the Bertran equations. In addition, we found the fundamental ν2, which should be independent of the FR interaction, shifted to higher wavenumbers as the concentration decreased. This shift was probably driven by the tuning of the FR. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Narrowing of the vibrational spectrum under compression of liquid carbon dioxide

The broadening and shift of the Q bands of the 1388/1285-cm−1 Fermi doublet of carbon dioxide have been measured by means of the spectroscopy of coherent anti-Stokes Raman scattering in a wide density range realized at compression in dense gaseous and liquid states. The spectrum of the low-frequency Q band exhibits an essential narrowing upon the compression of the liquid in the density range of 320–400 amagat from a maximum width of about 2.2 cm−1 to about 1.7 cm−1 determined by elastic dephasing. The observed dependence is connected with the progressive narrowing of the spectral contribution attributed to the collapsed rotational structure.

Hydrogen Bonding and Solvent Polarity Markers in the UV Resonance Raman Spectrum of Tryptophan: Application to Membrane Proteins

Ultraviolet resonance Raman (UVRR) spectra of tryptophan compounds in various solvents and a model peptide are presented and reveal systematic changes that reflect solvent polarity, hydrogen bond strength, and cation-pi interaction. The commonly utilized UVRR spectral marker for environment polarity that has been based on off-resonance Raman data, the tryptophan Fermi doublet ratio I1360/I1340, exhibits different values in on- and off-resonance Raman spectra as well as for different tryptophan derivatives. Specifically, the UVRR Fermi doublet ratio for indole ranges from 0.3 in polar solvents to 0.8 in nonpolar solvents, whereas the respective values reported here and previously for off-resonance Raman spectra are 0.5-1.3. UVRR Fermi doublet ratios for the more biologically relevant molecule, N-acetyl tryptophan ethyl ester (NATEE), are in a smaller range of 1.1 (polar solvent) to 1.7 (nonpolar solvent) and correlate to the solvent polarity/polarization parameters pi* and ETN. As has been reported previously, several UVRR modes are also sensitive to the hydrogen bond strength of the indole N-H moiety. Here, we report a new unambiguous marker for H-bonding: the ratio of the W10 (approximately 1237 cm-1) intensity to that of the W9 (approximately 1254 cm-1) mode (RW10). This ratio is 0.7 for NATEE in the absence of hydrogen bond acceptors and increases to 3.1 in the presence of strong hydrogen bond acceptors, with a value of 2.3 in water. The W8 and W17 modes shift more than +10 and approximately -5 cm-1 upon increase in hydrogen bond strength; this range for W17 is smaller than that reported previously and reflects a more realistic range for proteins and peptides in solution. Finally, our data provide evidence for change in the W18 and W16 relative intensity in the presence of cation-pi interactions. These UVRR markers are utilized to interpret spectra of model membrane-bound systems tryptophan octyl ester and the peptide toxin melittin. These spectra reveal the importance of intra- and intermolecular hydrogen bonding and cation-pi interactions that likely influence the partitioning of membrane-associated biomolecules to lipid bilayers or self-associated soluble oligomers. The UVRR analysis presented here modifies and augments prior reports and provides an unambiguous set of spectral makers that can be applied to elucidate the molecular microenvironment and structure of a wide range of complex systems, including anchoring tryptophan residues in membrane proteins and peptides.

Characterization of Carbon Dioxide Mobile Phase Density Profiles in Packed Capillary Columns by Raman Microscopy

Efforts to understand and optimize separations employing compressible mobile phases have been limited by a lack of understanding of the mobile phase density gradient. Mobile phase compressibility leads to gradients in linear velocity and solute retention and affects separation speed and efficiency, especially in packed columns. Gas chromatography (GC), supercritical fluid chromatography (SFC), and solvating gas chromatography (SGC) each rely on compressible mobile phases. This work describes the on-column density measurement of carbon dioxide, a common carrier fluid for SFC and SGC, in packed capillary columns using Raman microspectroscopy of the position of the Fermi doublet. Correlation of the spectrum with density was calibrated over a pressure range of 15 to 290 atm at 125 and 150 degrees C, which then allowed for determination of the density gradient of fluid flowing through a packed capillary column. The results of this work will be used to model the flow behavior of compressible fluids to understand the effects of mobile phase compressibility on separation speed and efficiency.

Molecular rotovibrational dynamics excited in optical filamentation

The rotovibrational dynamics excited by optical filamentation in molecular gases is studied in the temporal domain. Two time-delayed replicas of the same laser pulse have been used to generate a first filament, for the rotovibrational excitation of the sample, and a second collinear filament probing the Raman dynamics. The Fermi doublet structure in CO(2) as well as the very fast stretching mode of H(2) were clearly resolved.

SERS of CO2on Cold-Deposited Cu: An Electronic Effect at a Minority of Surface Sites⊥

We compare the results of surface enhanced Raman scattering (SERS) and infrared reflection absorption spectroscopy (IRRAS) of carbon dioxide (CO2) on cold-deposited copper films. The SERS spectra of CO2 on copper films deposited at 40 K display neutral species at SERS active sites with bands not observed by Raman spectroscopy of CO2 gas, but identical to the loss bands of gaseous CO2 in electron energy loss spectroscopy. The absence of one component of the Fermi doublet of CO2 in SERS proves that the local electromagnetic field enhancement at SERS active sites cannot deliver signals above the noise level. The activated anionic CO2− is observed by transient electron transfer from the anionic molecule to the copper metal at a subgroup of SERS active sites, which are annealed below 200 K. The IRRAS spectra show only the expected infrared (IR) active modes of neutral CO2 representing the “majority species” of adsorbed CO2.

Transient dimer formation in supercritical carbon dioxide as seen from Raman scattering

The polarized and depolarized Raman profiles of supercritical CO(2) have been measured in the region of the nu(2) bending mode (forbidden transition at about 668 cm(-1)) and for the Fermi dyad (1285 and 1388 cm(-1)) along the isotherms 307, 309, 313, and 323 K in a reduced density domain 0.04<rho*=rhorho(C)<2.04 (rho(C) approximately 467.6 kg m(-3), rho(C) is the critical density). The spectral features associated with the nu(2) mode (degeneracy removal of the mode and Raman intensity activation) are found to be due to the formation of transient complexes. This is supported by the spectral signatures predicted for parallel slipped dimer and trimers (cyclic and noncyclic) from ab initio calculations taking into account the frequency anharmonicity. The band-shape analysis of the Fermi doublet (observed in the spectral range of 1260-1400 cm(-1)) shows that on the subpicosecond time scale of the Raman spectroscopy, a tagged CO(2) molecule probed two kinds of environment in its first shell of neighbors independent of local density enhancement phenomenon. The first one involves interactions of CO(2) with surrounding molecules in the first shell whereas the latter is associated with a transient dimer formation. Finally, a broad band observed between the Fermi dyad (at about 1335 cm(-1)) is assessed from symmetry considerations and from its depolarization ratio as a further evidence of transient complex formation in supercritical CO(2).

Micro-Raman Thermometer for CO2 Fluids: Temperature and Density Dependence on Raman Spectra of CO2 Fluids

Abstract Raman spectra of CO2 fluids were measured at 288–329 K and densities of 0.81–1.16 g/cm3. The peak area ratios of hot bands at 1265 and 1408 cm−1 and Fermi doublet peaks at 1388 and 1285 cm−1 were correlated linearly with temperature. The peak area ratios are correlated with density. Calculation of the relationship between the peak area ratio, temperature, and density was achieved. Micro-Raman analysis enabled in situ temperature measurement of CO2 fluid with high spatial resolution.

An investigation into the effect of potassium ions on the folding of silk fibroin studied by generalized two‐dimensional NMR–NMR correlation and Raman spectroscopy

We used generalized two-dimensional NMR-NMR correlation to examine the effect of potassium ions on the conformation transition in silk fibroin to investigate the possibility that the fairly high K+ ion content found in the distal end of silk-secreting ducts in the silkworms could have a bearing on natural formation of the silk fiber. This has enabled us to propose a detailed mechanism for the transition process. Our evidence indicates that increasing the [K+] from 0 to 3.7 mg.g(-1) in the silk fibroin, as is thought to occur as the silk fibroin moves through the secretory pathway to the spigot, produces a sequence of secondary structural changes: helix and/or random coil-->helix-like-->beta-sheet-like-->beta-sheet. The sequence is the same as that produced in silk fibroin films by decreasing the pH of fibroin from 6.8 to 4.8. In addition, we used Raman spectroscopy to study the effect of K+ ions on the Fermi doublet resonance of the tyrosyl phenolic ring at 850 and 830 cm(-1). The intensity ratio I(850)/I(830) at these wave numbers indicated that the hydrogen bonding formed by the tyrosyl phenolic-OH becomes more stable with an increase in the K+ ion concentration as above. Our investigation on the effect of K+ ions on fibroin may help provide a theoretical basis for understanding the natural silk-spinning process and the conditions required for biomimetic spinning. It may also have relevance to the aggregation of other beta-sheet proteins, including prion proteins, neurofibrillary proteins and amyloid plaques.

Fermi resonance in CO2: A combined electronic coupled-cluster and vibrational configuration-interaction prediction

The authors present a first-principles prediction of the energies of the eight lowest-lying anharmonic vibrational states of CO(2), including the fundamental symmetric stretching mode and the first overtone of the fundamental bending mode, which undergo a strong coupling known as Fermi resonance. They employ coupled-cluster singles, doubles, and (perturbative) triples [CCSD(T) and CCSDT] in conjunction with a range of Gaussian basis sets (up to cc-pV5Z, aug-cc-pVQZ, and aug-cc-pCVTZ) to calculate the potential energy surfaces (PESs) of the molecule, with the errors arising from the finite basis-set sizes eliminated by extrapolation. The resulting vibrational many-body problem is solved by the vibrational self-consistent-field and vibrational configuration-interaction (VCI) methods with the PESs represented by a fourth-order Taylor expansion or by numerical values on a Gauss-Hermite quadrature grid. With the VCI, the best theoretical estimates of the anharmonic energy levels agree excellently with experimental values within 3.5 cm(-1) (the mean absolute deviation). The theoretical (experimental) anharmonic frequencies of the Fermi doublet are 1288.9 (1285.4) and 1389.3 (1388.2) cm(-1).

Comparative study of infrared and Raman spectra of CCl 4 in vapour and condensed phases: Effect of LO–TO splitting resulting from hetero-isotopic TD–TD interactions

Salient features of an in-depth comparative study of infrared and Raman spectra of CCl 4 in vapour, liquid and condensed phases are presented. Wavenumbers of ν 4, ν 1 + ν 4, ν 3 and 2ν 3 modes of CCl 4 vapour in infrared and Raman spectra are found to be in good agreement. Analysis of the vibrational spectra of liquid CCl 4 together with the spectroscopic observations on solid CCl 4 at low temperatures reveal TD–TD interaction amongst various CCl 4 isotopes in condensed states. The concept of LO–TO splitting of dipole active ν 3 and ν 1 + ν 4 Fermi doublet have been invoked to explain several features of the vibrational spectra of liquid CCl 4. There is significant strengthening of Fermi resonance interaction between ν 3 and ν 1 + ν 4 modes of CCl 4 in condensed phases relative to that in vapour phase. The Fermi resonance interaction parameter W has been found to be independent of molecular environment.

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

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.