Infrared and Raman study of the interaction between methyl acetate and phenol derivatives

In previous publications [1–3], we have been concerned with the influence of hydrogen bond formation on the Raman intensity of the carbonyl stretching vibration. It has been shown that hydrogen bond association of simple carbonyl bases (cyclohexanone, acetone, acetophenone) with proton donors such as phenol derivatives, hydrochlorid or hydrobromic acid brings about an intensity increase of the ν_CO Raman band; moreover, the intensity enhancement is linearly related to the enthalpy of complex formation. In the present work, these measurements are extended to the complexes formed between methyl acetate (MeAc) and phenol derivatives.

As suggested by the frequency lowering of the ν_CO vibration and the frequency increase of the ν_CO band, complex formation in solution takes place on the carbonyl function.From NMR [4–5] and UV data [6] it can also be concluded that protonation via hydrogen-bonded attachment occurs in solution predominantly at the carbonyl oxygen atom.Literature data for the thermodynamic quantities referring to esters with hydroxylic compounds are scarce. Consequently in this work, we have determined the equilibrium constants and the enthalpy of formation for complexes between MeAc and phenol derivatives. We also report the absolute intensity of the ν_CO Raman band in the free ester molecule and in the complexes, all measurements been made in a solvent of low polarity : carbontetrachloride.     

Variation of Dipole Moment Function of O-H Bond of t-Butanol with the Nature of Solvent and Its Temperature

The intermolecular influence on dipole moment function is evaluated for O-H bond of t-butanol in different nonpolar solvents at temperatures ranging from 10° to 60°C employing IR band intensities of fundamental and first overtone bands. Two sets of dipole moment derivatives have been calculated corresponding to – and +- combinations of the transition moment matrix elements R₁₀ and R₂₀, the values for ++ and -+ combinations are equal in magnitude to those for - and +- combinations, respectively and opposite in signs. In general the dipole moment derivatives increase on lowering the temperature as well as with increasing molecular interactions with the solvent molecules. Dipole moment plots with dimensionless coordinate ξ [=(r-r_e)/r_e, where r and r_e are internuclear distances during vibration and at equilibrium, respectively] are reported for various systems considered. It is found that for +- combination the dipole moment maximum shifts to higher internuclear distances when polarisation of the solute molecules is increased by lowering of temperature or increase in molecular interactions between solute and solvent molecules. A reverse trend is observed for – combination.- The OH band of t-butanol vapor has been measured.     

The structure and vibrational spectral parameters of a complex of HF with the planar (H<Subscript>2</Subscript>CO)<Subscript>2</Subscript> dimer

Equilibrium nuclear configurations of the planar formaldehyde homodimer (H₂CO)₂ and the (H₂CO)₂···HF complex are determined in the MP2/6-311++G(3df, 3pd) approximation taking into account the superposition error of basis sets of monomers. Harmonic values of the frequencies and intensities of fundamental transitions between vibrational states of these hydrogen-bonded complexes were calculated using the Gaussian 09 package of programs. Anharmonic values of the frequencies and intensities of the ν(H–F) stretching vibration and several intermolecular vibrations in the (H₂CO)₂···HF trimer were obtained from variational solutions of one-, two-, and three-dimensional vibrational Schrödinger equations. The anharmonic influence of the C=O and hydrogen bond O···H–F stretching vibrations, as well as of librational vibrations of monomers, on the spectral parameters of the strongest ν(H–F) absorption band of trimer was studied.     

Broadening of vibrational-rotational lines of the H2S molecule by pressure of monatomic gases

Optimal sets of parameters for a model intermolecular potential that provide the best reproduction of broadening coefficients γ for the absorption lines in the ν₂ band of the H₂S molecule are determined for systems H₂S-A (A = He, Ne, Ar, Kr, and Xe). For H₂S-He, the potential is obtained with the temperature dependence of coefficients γ taken into account for two rotational absorption lines 1₁₀ ← 1₀₁ and 2₁₁ ← 2₀₂. With the potentials obtained, the coefficients γ are calculated for the ν₁ and ν₃ bands and compared with the available experimental data. There are significant discrepancies between the calculated and experimental values of γ.     

Spectral intensities in the ν3 bands of 12CH4 and 13CH4

Relative and absolute line intensities for the ν₃ bands of the ¹²C and ¹³C isotopic varieties of methane have been measured using a tunable difference-frequency laser spectrometer. From these data the integrated band strength of ¹³CH₄ is calculated to be 0.983 ± 0.007 that of ¹²CH₄, with the uncertainty representing three standard deviations. The absolute ν₃ bandstrength for ¹²CH₄ is 266.1 ± 3.0 cm^?2 atm ^?1 at 294.7 K where the errors are dominated by the pressure measurement. This band strength corresponds to an effective transition moment 〈μ₃〉 = 0.0534(3)D for ¹²CH₄ from which the ν₄ band dipole moment and the Herman-Wallis F factor can be estimated using a recent force field model for methane.     

Transferability of dipole moment derivatives: Calculation of absolute rotational contributions for symmetrical molecules

It is shown that Polo's method for the calculation of the D^?1 and G^?1 matrices can be extended to the calculation of the absolute rotational contributions involved in the molecular dipole moment derivatives in terms of symmetry coordinates. The method applies to both stretching and bending modes. The method is outlined for AB₃ (C_3v) molecules.     

Stark spectroscopy with the CO laser: The ν3 fundamental band of H2CO

The ν₃ fundamental band of H₂CO (CH₂ scissoring motion) has been studied by means of CO laser Stark spectroscopy and conventional infrared absorption spectroscopy. The primary aim of the work was to determine the dipole moment of H₂CO in the v₃ = 1 state, and the value determined was 2.3250 ± 0.0025 D. The spectrum was analyzed with the inclusion of the Coriolis interactions among ν₃, ν₄, and ν₆ so that “true” rotational constants were determined for ν₃; “effective” constants obtained by ignoring these interactions were also determined. The ν₃ band origin was determined to be 1500.174 ± 0.002 cm^?1. The H₂CO spectrum was also used as a means of determining the frequencies of some ¹³C¹⁶O and ¹²C¹⁸O laser lines in the 1500 cm^?1 region relative to ¹²C¹⁶O lines.     

On the mechanism of the broadening of the proton vibrational IR band in weak hydrogen bonds. Double adiabatic approximation

It is proposed that broadening of the ν_s (AH) IR band is due to the ν_s (AH) and ν_σ (AH…B) mode coupling and to the stochastic variation of the equilibrium distance R_e (A…B) modulating the proton vibration. The R_e disordering variation is caused by a coupling of the ν_σ mode with the low frequency oscillators (ν_Q) of the medium and of the complex as such. Besides, the (ν_σ, ν_Q) and (ν_s, ν_σ) couplings cause a ν_s frequency shift. Both the band broadening and the frequency shift increase with higher force constants responsible for (ν_σ, ν_Q) mode coupling. Furthermore the Q_i low frequency stochastic vibrations directly modulate the ν_σ (AH…B) vibration and the free AH groups stretching vibration (ν^o_s) causing some broadening at their bands which is however several times smaller than the ν_s band broadening in the complex. Several examples are reported to confirm the proposed model.     

On the application of the theory of the brownian movement in a periodic potential to the study of inertial effects and dipole coupling

For a series of ten electron molecules (HF, H₂O, NH₃, CH₄) the molecular polarizability tensor and the derivatives with respect to the symmetry coordinates have been calculated from ab initio SCF wavefunctions using the finite field method as well as perturbation theory approaches. Raman intensities and degrees of depolarization derived from the finite field results agree well with the available experimental data.

The zeroth order bond polarizability model and the atom dipole interaction model have been analysed. Both models can be used to describe the computed static polarizabilities and the derivatives with respect to bond stretching, but fail for the derivatives with respect to the bending coordinates.     

Photoelectron spectra of ethylene and of the six deuterated derivatives

The photoelectron spectra of C₂H₄ and of six deuterated molecules of ethylene — C₂D₄, C₂D₃H, C₂H₃D, cis-C₂H₂D₂, trans-C₂H₂D₂ and gem-C₂H₂D₂ — have been recorded with the 584-Å resonance line of He. The adiabatic ionization potentials of the X²B_3u and the ²B_3g states of the seven isotopic components have been determined with an accuracy of about 7 meV. The ionization potentials of the other excited electronic states have been measured with a lower accuracy owing to a less well defined onset. The measured ionization potentials of C₂H₄ are 10.514 eV, 12.431 eV, 14.4₃ eV, 15.7₄ eV and 18.7 eV. The vibrational structure of the first electronic band shows that the two normal modes ν₂ (symmetric CC stretching) and ν₃ (symmetric HCH bending) are excited simultaneously. The measured vibrational frequencies show no abnormal isotopic effect if the assignment given in the literature for the ν₂ and ν₃ modes in C₂H₄⁺ are reversed and if a stronger excitation of the ν₃ symmetric bending mode in the least deuterated compounds is assumed. The vibrational modes most strongly excited in the second and third electronic bands are ν₁ (symmetric CH stretching) and ν₃, and in the fourth band ν₃.     

High-Resolution Fourier Transform Infrared Spectrum of the ν1+ν3 Band System of HCCH

A high-resolution vibration-rotation overtone spectrum of H¹³C¹²CH has been recorded with a Fourier transform infrared spectrometer in the wavenumber region 6400 to 6700 cm⁻¹. The main band, assigned as the C-H stretching combination band ν₁+ν₃, and some overtone and hot bands have been rotationally analyzed. Altogether eight parallel bands have been observed. The vibrational labels have been deduced on the basis of the assignments of the fundamental ν₃ antisymmetric C-H stretching band system.     

Absolute infrared intensities in some metal carbonyls and the charge flux model of the dipole derivatives

The absolute intensities of the four infrared active modes of certain metal carbonyls, M(CO)₄ or M(CO)₆, are analyzed from the point of view of the equilibrium charge-charge flux model of the dipole derivatives. It is shown that the charges obtained from the bending modes, assuming negligible flux for these modes, are apparently identical with those reported by previous authors. However, such charges are much too sensitive to the choice of L matrix (which transforms the normal coordinates to symmetry coordinates) to permit any conclusions. The carbonyl stretching mode implies values of the dipole derivative three- to sixfold greater than in gaseous CO. It seems most reasonable to attribute most of this enhancement to charge flux between the metal and carbon atoms.     

Fourier-Transform Infrared (FTIR) studies on the hydration of extractant anions in microemulsions

The hydration of extractant anions was observed by using the subtraction technique to measure the change of band intensities on FTIR. The variation of absorption peaks of ν_s (COO-), ν_as (COO-), ν (P-O-C), ν (P), ν (S) and ν (S-O-C) and their oscillator strengths with the amount of H₂O added has been quantitatively recorded. The results have been explained by the formation of H-bonds between the extractant anions and the H₂O molecule.     

Effective dipole moment of rotational transitions of X 2 Y molecules

Contributions determining the rotational dependence of the effective dipole moment of molecules are calculated for the ground state of H₂S and H₂O molecules. The calculation is carried out in various ordering algorithms of perturbation theory. It is shown that the convergence of the effective dipole moment for the ground state of an H₂O molecule in the polynomial representation is rather slow in the rotational operator J _z (the convergence radius is K*≤17). Nonpolynomial forms of the dipole moment as a function of rotational operators are discussed.     

Vibrational spectroscopic study of lithium intercalation into LiTi2(PO4)3

Ex situ vibrational spectra are recorded during the first discharge of LiTi₂(PO₄)₃. Spectral changes are consistent with a two-phase model for the electrochemical insertion of Li⁺ ions. Differences in the frequencies and relative intensities of the LiTi₂(PO₄)₃ and Li₃Ti₂(PO₄)₃ bands are due to changes in the effective force constants, dipole moment derivatives, and polarizability derivatives as Li⁺ is inserted into LiTi₂(PO₄)₃. The intramolecular PO₄³⁻ bending modes (ν₂ and ν₄) are found to be more sensitive to Li⁺ insertion than the intramolecular PO₄³⁻ stretching modes (ν₁ and ν₃). This is because ν₂ and ν₄ are less localized than ν₁ or ν₃ and are more susceptible to small structural changes in the unit cell. Furthermore, a band at 487 cm^− 1 appears in the infrared spectrum of Li₃Ti₂(PO₄)₃. This band is assigned as a Li⁺ ion cage mode and is due to Li⁺ ions that occupy the M(3) and M′(3) sites in the Li₃Ti₂(PO₄)₃ structure. A small degree of band broadening is also detected in the vibrational spectra when Li⁺ ions are inserted, which might indicate some disordering in the cathode material.     

Raman spectroscopy of smithsonite

Raman spectroscopy at both 298 and 77 K has been used to study a series of selected natural smithsonites from different origins. An intense sharp band at 1092 cm⁻¹ is assigned to the CO₃²⁻ symmetric stretching vibration. Impurities of hydrozincite are identified by a band around 1060 cm⁻¹. An additional band at 1088 cm⁻¹ which is observed in the 298 K spectra but not in the 77 K spectra is attributed to a CO₃²⁻ hot band. Raman spectra of smithsonite show a single band in the 1405–1409 cm⁻¹ range assigned to the ν₃ (CO₃)²⁻ antisymmetric stretching mode. The observation of additional bands for the ν₃^g modes for some smithsonites is significant in that it shows distortion of the ZnO₆ octahedron. No ν₂ bending modes are observed for smithsonite. A single band at 730 cm⁻¹ is assigned to the ν₄ in phase bending mode. Multiple bands be attributed to the structural distortion are observed for the carbonate ν₄ in phase bending modes in the Raman spectrum of hydrozincite with bands at 733, 707 and 636 cm⁻¹. An intense band at 304 cm⁻¹ is attributed to the ZnO symmetric stretching vibration. Copyright © 2007 John Wiley & Sons, Ltd.     

The Hot Bands of Methane between 5 and 10 μm

Experimental line intensities of 1727 transitions arising from nine hot bands in the pentad–dyad system of methane are fitted to first and second order using the effective dipole moment expansion in the polyad scheme. The observed bands are ν₃− ν₂, ν₃− ν₄, ν₁− ν₂, ν₁− ν₄, 2ν₄− ν₄, ν₂+ ν₄− ν₂, ν₂+ ν₄− ν₄, 2ν₂− ν₂, and 2ν₂− ν₄, and the intensities are obtained from long-path spectra recorded with the Fourier transform spectrometer located at Kitt Peak National Observatory. For the second order model, some of the 27 intensity parameters are not linearly independent, and so two methods (extrapolation and effective parameters) are proposed to model the intensities of the hot bands. In order to obtain stable values for three of these parameters, 1206 dyad (ν₄, ν₂) intensities are refitted simultaneously with the hot band lines. The simultaneous fits to first and second order lead to rms values respectively of 21.5% and 5.0% for the 1727 hot band lines and 6.5% and 3.0% for the 1206 dyad lines. The band intensities of all 10 pentad–dyad hot bands are predicted in units of cm⁻²atm⁻¹at 296 K to range from 0.931 (for 2ν₄− ν₄) to 7.67 × 10⁻⁵(for 2ν₄− ν₂). The total intensities are also estimated to first order for two other hot band systems (octad–pentad and tetradecad–octad) that give rise to weak transitions between 5 and 10 μm.     

The structural independence of Raman scattering cross sections of ν1(NO3−) and ν(H2O)

The Raman scattering cross section (RSCS) is an important parameter in the applications of Raman spectroscopy to make quantitative analysis. To date, the dependence of the RSCS on concentration has remained unclear. Nitrate aerosols can easily achieve a supersaturated state, which provides a way to obtain the RSCS especially under this state. In this study, Raman spectra of NaNO₃ and Mg(NO₃)₂ solutions are obtained with molar water‐to‐solute ratios (WSRs) ranging from 84.2 to 2.30 and 93.8 to 7.32, respectively. With decreasing WSR, a shift to higher wavenumbers of the symmetric stretching band of nitrate ion, i.e. ν₁(NO₃⁻), is observed, indicating the formation of various ion pairs. Meanwhile, the area ratio between the strongly and weakly hydrogen‐bonded components of water O H stretching envelope, i.e. ν(H₂O), reduces as the WSR decreases, implying the transformation of water molecules from strong hydrogen‐bonding structures to the weak ones. However, a good linear relationship is revealed between the integrated intensity ratio of the ν(H₂O) band to ν₁(NO₃⁻) band and WSR. The results suggest that the RSCSs of NO₃⁻ and H₂O are insensitive to the structures of both ion pairs and hydrogen‐bonding structures. This observation points to the possibility of conducting quantitative analysis through the area ratio of the ν(H₂O) band to the ν₁(NO₃⁻) band with Raman spectra without considering the formation of ion pairs and the variation of the hydrogen‐bonding structure. Copyright © 2011 John Wiley & Sons, Ltd.     

Cyclopropane-d6: The C–D Stretching Bands ν6and ν8at High Resolution

The two infrared active C–D stretching bands ν₆and ν₈of C₃D₆were recorded on a large Fourier transform spectrometer with a linewidth close to the Doppler–Fizeau limit. The perpendicular band of theE′ vibration ν₈near 2209.6 cm⁻¹is found to be highly perturbed by anharmonic resonances with the states ν₇+ 3ν₁₄, ν₇+ ν₉+ ν₁₄, and ν₄+ ν₁₀+ ν₁₄, and by aJ_x,yCoriolis-type interaction with an unidentified[formula]state. In contrast, the structure of the parallel band of the[formula]vibration ν₆near 2336.7 cm⁻¹appears to be relatively unperturbed. Spectroscopic constants are reported for the two fundamentals and for some of the perturbers of the ν₈state.