Unusual infrared spectrum of ethane adsorbed by gallium oxide

The present study reports an unusual diffuse reflection Fourier transform (DRIFT) spectrum of ethane adsorbed by gallium oxide. One of the stretching C-H bands in this spectrum with a maximum at 2753 cm(-1) is more than by 100 cm(-1) shifted toward lower frequencies in comparison with gaseous ethane. In addition, the relative intensity of this band is unusually high. This indicates a very strong polarizability of the corresponding chemical bonds resulting from perturbation of ethane by the low coordinated Ga(3+) cations. The assignment of this band to the very strongly perturbed initially fully symmetric nu(1) C-H stretching vibration is confirmed by a DFT modeling of ethane adsorption by the simplest Ga(2)O(3) cluster. The obtained results also indicate heterolytic dissociative adsorption and dehydrogenation of ethane by Ga(3+) Lewis sites at elevated temperature. This is evidenced by the appearance of new IR bands from zinc alkyl fragments and acidic protons followed by decomposition of resulting zinc ethyl species. In parallel, the most intense IR band at lower frequency from the most strongly polarized C-H chemical bond decreased in intensity. The obtained results indicate that these vibrations are involved in subsequent heterolytic dissociative adsorption. The obtained results demonstrate that, similar to the shifts of C-H stretching vibrations to the low-frequency, intensities of IR C-H stretching bands can be also used as an index of chemical activation of adsorbed paraffins via their polarization by the low-coordinated cations.     

Intensities of C-H IR stretching bands of ethane and propane adsorbed by zeolites as a new spectral criterion of their chemical activation via polarization resulting from stretching of chemical bonds

Polarization of ethane and propane resulting from adsorption of these hydrocarbons by protons and different cations in mordenite, ZSM-5, and Y zeolites was studied by diffuse reflection Fourier transform IR spectroscopy (DRIFTS). Perturbation of adsorbed molecules by protons and sodium cations is weak, while positions of absorption bands for both these zeolites are very close to each other. In contrast, distributions of C-H IR stretching bands in intensities are somewhat different. This effect is pronounced much stronger for adsorption of light paraffins by bivalent alkaline earth and zinc cationic forms of these zeolites. Distribution of relative intensities of absorption bands strongly depends in this case both on the nature of cations and on the zeolites, while the most strongly perturbed vibrations are the initially fully symmetric C-H stretching vibrations. The corresponding low-frequency shifts and relative intensities of IR bands are increasing for different cations and zeolites in the following sequences: Na < Ca < Mg < Zn and Y < Mor approximately ZSM-5, while the difference in distribution of relative intensities of C-H stretching bands is pronounced much stronger than for the low-frequency shifts of these bands. Therefore, the relative intensities of IR C-H stretching bands are much better criterion of perturbation of light paraffins upon adsorption than the frequencies of these bands, which are traditionally used for this purpose. In addition, distribution of C-H IR stretching bands in intensity also provides unique information on anisotropy of polarizability of different C-H bonds created by their vibrations. For the acid and acid-base catalysis, where the main source of chemical activation arises from polarization of adsorbed molecules, such information is most important, while the anisotropy of polarizability provides a unique information on selective activation of different chemical bonds resulting from their stretching. The obtained results also demonstrate the possibility to use for testifying of the strength of Lewis acid sites instead of adsorption of the model molecular probes adsorption of the paraffins themselves.     

Use of the IR spectra of adsorbed ethane and propane molecules to characterize the strength of active sites in zeolites and to analyze the activation of C-H bonds in these paraffins

The adsorption and activation of ethane and propane on the hydrogen and cationic forms of mordenite, zeolite ZSM-5, and zeolite Y were studied by diffuse-reflectance IR spectroscopy. The effect of the polarization of these molecules by adsorption sites on the intensities and shifts of absorption bands due to C-H stretching vibrations were studied. It was found that weak adsorption species were formed on the hydrogen forms of the above zeolites. In this case, both the intensity distributions and the positions of absorption bands due to C-H stretching vibrations were almost independent of the nature of zeolites. However, both absorption band maximum positions and relative intensity distributions changed upon paraffin adsorption on the cationic forms. It was also found that relative intensity distributions and shifts of absorption bands due to C-H stretching vibrations strongly depended on the nature of cations and zeolites. In this case, the initially totally symmetrical C-H vibrations were found most strongly disturbed. The low-frequency shifts and relative intensities of absorption bands due to these vibrations for various cations and zeolites were found to increase in the following orders: H < Na < Ca < Mg < Zn and zeolite Y < Mord ≈ ZSM-5. The experimental results suggest that ethane and propane molecules can be used as molecular probes for acquiring information on the nature and properties of acidbase sites in zeolites. In this case, both the low-frequency shifts and the relative intensities of absorption bands due to C-H stretching vibrations can be used as measures to characterize the nature of cations and zeolites. However, the latter was found to be much more sensitive to the nature of active sites.     

IR Spectra of Ethane Adsorbed on the Hydrogen,Sodium, and Zinc Forms of a Y-Type Zeolite: Interpretation Using <Emphasis Type="Italic">ab initio</Emphasis> Quantum Chemical Calculations

Ethane adsorption on the hydrogen, sodium, and zinc forms of faujasite brings about polarization anisotropy of the C-H stretching vibrations. This anisotropy shows itself most clearly as perturbation of the vibrational mode analogous to the breathing C-H mode ν₁ of free ethane. The relative intensity and the low-frequency shift of the absorption band due to the distorted ν₁ mode increase with increasing perturbation caused by the C₂H₆-adsorption site interaction. The polarizing power of adsorption sites increases in the order H⁺ < Na⁺ < Zn²⁺. The C-H stretching vibrations in ethane adsorbed on the cationic forms of the Y zeolite are not symmetry-forbidden; accordingly, adsorbed ethane gives more absorption bands than gaseous ethane. The interaction between ethane and zinc cations in the Y zeolite structure eliminates not only the symmetry forbiddenness but also the twofold degeneracy of the C-H stretches.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 434–440.Original Russian Text Copyright © 2005 by Pidko, Kazanskii.     

Molecular dynamics simulation of liquid methanol. II. Unified assignment of infrared, Raman, and sum frequency generation vibrational spectra in methyl C-H stretching region

Vibrational spectra of methyl C-H stretching region are notoriously complicated, and thus a theoretical method of systematic assignment is strongly called for in condensed phase. Here we develop a unified analysis method of the vibrational spectra, such as infrared (IR), polarized and depolarized Raman, and ssp polarized sum frequency generation (SFG), by flexible and polarizable molecular dynamics simulation. The molecular model for methanol has been developed by charge response kernel model to allow for analyzing the methyl C-H stretching vibrations. The complicated spectral structure by the Fermi resonance has been unraveled by empirically shifting potential parameters, which provides clear information on the coupling mechanism. The analysis confirmed that for the IR, polarized Raman, and SFG spectra, two-band structure at about 2830 and 2950 cm(-1) results from the Fermi resonance splitting of the methyl C-H symmetric stretching and bending overtones. In the IR spectrum, the latter, higher-frequency band is overlapped with prominent asymmetric C-H stretching bands. In the depolarized Raman spectrum, the high frequency band at about 2980 cm(-1) is assigned to the asymmetric C-H stretching mode. In the SFG spectrum, the two bands of the splitted symmetric C-H stretching mode have negative amplitudes of imaginary nonlinear susceptibility χ(2), while the higher-frequency band is partly cancelled by positive imaginary components of asymmetric C-H stretching modes.     

Diffuse-Reflectance IR Spectra of ortho-Hydrogen and para-Hydrogen Adsorbed on Zeolite BaX at 77 K and Their Interpretation in Terms of the Stark Effect

The vibrational and vibrational–rotational spectra of hydrogen adsorbed on zeolite BaX at 77 K were examined by diffuse-reflectance IR spectroscopy over a wide range of wavenumbers. The use of hydrogen enriched in the para isomer and of molecular deuterium allowed us to reliably assign the absorption bands to orthohydrogen and para-hydrogen and compare the experimentally observed band splitting with the theoretically calculated shifts of the corresponding levels resulted from the Stark effect. In the calculations, an adsorption site was simulated as a positive point charge. Although this approximation is rough, the IR spectra of adsorbed hydrogen and deuterium are adequately described in terms of the Stark effect. A decrease in the frequency of stretching vibrations of H–H (D–D) bonds in the molecules coordinated to Ba²⁺ cations, a decrease in the intensity of vibrational–rotational absorption bands, and the band splitting in the spectra of adsorbed para-hydrogen and orthohydrogen were explained.     

On two alternative mechanisms of ethane activation over ZSM-5 zeolite modified by Zn2+ and Ga1+ cations

The activation of ethane over zinc- and gallium-modified HZSM-5 dehydrogenation catalysts was studied by diffuse reflectance infrared spectroscopy. Hydrocarbon activation on HZSM-5 modified by bivalent Zn and univalent Ga cations proceeds via two distinctly different mechanisms. The stronger molecular adsorption of ethane by the acid-base pairs formed by distantly separated cationic Zn2+ and basic oxygen sites results already at room temperature in strong polarizability of adsorbed ethane and subsequent heterolytic dissociative adsorption at moderate temperatures. In contrast, molecular adsorption of ethane on Ga+ cations is weak. At high temperatures dissociative hydrocarbon adsorption takes place, resulting in the formation of ethyl and hydride fragments coordinating to the cationic gallium species. Whereas in the zinc case a Br?nsted acid proton is formed upon ethane dissociation, decomposition of the ethyl fragment on gallium results in gallium dihydride species and does not lead to Br?nsted acid protons. This difference in alkane activation has direct consequences for hydrocarbon conversions involving dehydrogenation.     

Stretching vibrations of CH bonds in spectra of dicarbaclosododecaboranes (p-, m-, and o-carboranes)

Parameters of bands corresponding to stretching vibrations of C-H bonds in spectra of o-, m-, and p-isomers of the icosahedral carborane B₁₀H₁₀C₂H₂ have been measured with high accuracy. The stretching vibrations of C-H bonds in spectra of o- and m-carborane (12), molecules which have C_2v point group symmetry, are demonstrated to appear the same as in the spectrum of the p-isomer with D_5d symmetry. The frequencies of Raman and IR lines practically coincide. This indicates the absence of interaction of the stretching vibrations of the two C-H bonds even in the o-carborane molecule.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2263–2267, October, 1989.     

Raman-spectral depolarisation ratios of ions in concentrated aqueous solution. The next-to-negligible effect of highly asymmetric ion surroundings on the symmetry properties of polarisability changes during vibrations of symmetric ions. Ammonium sulphate and tetramethylammonium bromide

Depolarisation ratios rho have been measured for the Raman spectra of solutions of composition (NH4)2 SO4*11H2O and (CH3)4NBr*29D2O. Even though the former's vibration spectrum shows clear evidence of lowered ion symmetries (presence of nu1 of SO4(2-) in the IR spectrum, IR versus R nu(max) shifts for nu3 and nu4 of SO4(2-) and nu4 of NH4+) nu1 of SO4(2-) has (apparent) rho of only 0.014, while nu2, nu3 and nu4 of SO4(2-) and nu4 (probably also nu2) of NH4+ have rho in the range 0.73-0.77; within the experimental error and base line uncertainty the latter are equal to 0.75, i.e. to rho(max) with the geometry of the optics used. For (CH3)4NBr symmetric N+-C stretching has rho 0.012; all-in-phase C-H stretching and four overtones in Fermi resonance with it have rho in the range 0.02-0.035, but the deviation from zero here is in part due to underlying or overlapping depolarised bands. The sufficiently well isolated antisymmetric CH stretching and degenerate CH bending bands again have rho in the range 0.74-0.76. These results show that the selection rules in respect of rho, which apply strictly only to isolated molecules, are for practical purposes still valid for molecules in strongly symmetry-distorting external environments in the liquid phase. More specifically: (A) During vibrations in which quasi-spherical intramolecular symmetry is retained, the externally caused aspherical component of the polarizability ellipsoid does not change aspherically to a sufficient extent for an appreciably intense anisotropic Raman band to appear. (B) During intramolecularly anti-symmetric vibrations of symmetric molecules, the portion of the externally caused distortion of the polarizability ellipsoid that fails to cancel over a whole vibration period is not large enough to give rise to an appreciably intense isotropic component of the Raman band. This means in practice rho for these Raman bands is still rho(max), even for concentrated aqueous solutions.     

Anharmonic effects in IR, Raman, and Raman optical activity spectra of alanine and proline zwitterions

The difference spectroscopy of the Raman optical activity (ROA) provides extended information about molecular structure. However, interpretation of the spectra is based on complex and often inaccurate simulations. Previously, the authors attempted to make the calculations more robust by including the solvent and exploring the role of molecular flexibility for alanine and proline zwitterions. In the current study, they analyze the IR, Raman, and ROA spectra of these molecules with the emphasis on the force field modeling. Vibrational harmonic frequencies obtained with 25 ab initio methods are compared to experimental band positions. The role of anharmonic terms in the potential and intensity tensors is also systematically explored using the vibrational self-consistent field, vibrational configuration interaction (VCI), and degeneracy-corrected perturbation calculations. The harmonic approach appeared satisfactory for most of the lower-wavelength (200-1800 cm(-1)) vibrations. Modern generalized gradient approximation and hybrid density functionals, such as the common B3LYP method, provided a very good statistical agreement with the experiment. Although the inclusion of the anharmonic corrections still did not lead to complete agreement between the simulations and the experiment, occasional enhancements were achieved across the entire region of wave numbers. Not only the transitional frequencies of the C-H stretching modes were significantly improved but also Raman and ROA spectral profiles including N-H and C-H lower-frequency bending modes were more realistic after application of the VCI correction. A limited Boltzmann averaging for the lowest-frequency modes that could not be included directly in the anharmonic calculus provided a realistic inhomogeneous band broadening. The anharmonic parts of the intensity tensors (second dipole and polarizability derivatives) were found less important for the entire spectral profiles than the force field anharmonicities (third and fourth energy derivatives), except for a few weak combination bands which were dominated by the anharmonic tensor contributions.     

Effect of the resonance of the C-H and O-H bond stretching vibrations on the IR spectra of the hydrogen bond in formic and acetic acid

It is shown that the resonance of the O-H and C-H bond stretching vibrations is responsible for a noticeable intensity redistribution effect in the IR spectra of associated formic acid molecules in the gaseous phase. This effect is manifested by a considerably high growth in intensity of the νC-H band, which overlaps the νO-H band contour in the spectra. A vibronic coupling of the Herzberg-Teller-type expressed by the second order term in the perturbation theory is the most probable source of these spectral effects. The presented mechanism explains the variation of the effect magnitude accompanying the phase transitions. The proposed model also facilitates the understanding of the H/D isotopic effects in the spectra as well as the essential difference in the corresponding spectral properties between the formic and the acetic acid.     

Diffuse Reflectance IR Spectra of Molecular Hydrogen and Deuterium Adsorbed on Zinc Oxide

Diffuse reflectance IR spectroscopy is used to study hydrogen and deuterium adsorption on zinc oxide at room temperature and 77 K. At room temperature, H₂ and D₂ molecules are dissociatively adsorbed with the formation of hydrides and hydroxy groups of three types. At 77 K, diffuse reflectance spectra reveal the bands from molecular hydrogen and deuterium in addition to the dissociatively adsorbed forms. The presence of several bands of stretching H–H and D–D vibrations points to the nonuniformity of adsorption sites. This nonuniformity is also confirmed by the fact that, after heating zinc oxide from 77 K to room temperature in an atmosphere of hydrogen, only an insignificant portion of adsorbed molecular hydrogen dissociates. Most of dissociatively adsorbed hydrogen is formed without a molecular precursor. The dissociation of H₂ and D₂ most likely occurs on very active adsorption species so rapidly that the molecular precursor is not observed. The bond energy in molecular deuterium precursors of dissociation estimated from the fundamental vibration frequency and the overtone of D–D vibrations suggests moderate excitation of the bond. This agrees well with the conclusion that the dissociative adsorption of hydrogen and deuterium occurs without a molecular precursor.     

The effect of hydrogen bonding interactions between 2-[4-(dimethylamino)phenyl]-3-hydroxy-4H-chromene-4-one in the ground and excited states and dimethylsulfoxide or methanol on electronic absorption and emission transitions

The surface state of optically pure polydisperse TiO₂ (anatase and rutile) was determined by infra-red (IR) spectroscopy analysis in the temperature range of 100–453 K. Anatase A300 spectrum, contrary to rutile R300 one, has a broad three-component absorption band with peaks at 1048, 1137 and 1222 cm⁻¹ in the spectral range of δ(Ti–O–H) deformation vibrations. For rutile R300 we observed a very weak band at 1047 cm⁻¹, and for the thermal treated rutile R900 these bands were not appeared at all. The analysis of temperature dependencies for the mentioned absorption bands revealed the spectral shift of 1222 cm⁻¹ band towards the high frequencies, when the temperature increased, but the spectral parameters of 1137 and 1048 cm⁻¹ bands remained the same. The temperature of 1222 cm⁻¹ band maximum shift was 373–393 K and correlated with DSC data. Obtained results allowed to assign 1222 cm⁻¹ band to the deformation vibrations of OH-groups, bounded to the surface adsorbed water molecules by weak hydrogen bonds (5 kcal/mol). During the temperature growth these molecules desorbed, which also resulted in the intensity decreasing of stretching OH-groups vibration IR-bands at 3420 cm⁻¹. The destruction and desorption of surface water complexes led to Ti–O–H bond strengthening. IR bands at 1137 and 1048 cm⁻¹ were attributed to the stronger bounded adsorbed water molecules, which are also characterized with stretching OH-groups vibration bands at 3200 cm⁻¹. These surface structure were additionally stabilized by hydrogen bonds with the neighbouring TiO₂ lattice anions and other OH-groups, and desorbed at higher temperatures.     

Blue shifts and unusual intensity changes in the infrared spectra of the enflurane···acetone complexes: spectroscopic and theoretical studies

Blue-shifting C-H···O hydrogen-bonded complexes between enflurane (CHFCl-CF(2)-O-CHF(2)) and deuterated acetone have been identified in CCl(4) solution by FT-IR spectroscopy. For the two ν(C-H) stretching vibrations of enflurane the observed blue shifts are +17 and +11 cm(-1). The corresponding two infrared ν(C-H) bands show the opposite changes of their intensity, one is decreasing, and the other is significantly increasing, upon formation of the hydrogen bonding. The structures, binding energies, and theoretical infrared spectra of the enflurane-acetone complexes were calculated by MP2 and B3LYP methods using the 6-311++G(d,p) basis set. The interaction energies were evaluated by the complete basis set limit (CBS) calculations at the HF, MP2, and CCSD(T) levels of theory. Although the MP2 method slightly overestimates the blue shifts, the MP2 predicted frequency difference and the relative IR intensities of two ν(C-H) stretching bands for the enflurane-acetone complexes show good agreement with experiment. Unfortunately, the B3LYP method predicts incorrect IR intensities of these hydrogen-bonded systems. The NBO analysis was performed to unravel the origin of the unusual intensity changes of two ν(C-H) stretching bands, in enflurane complexes.     

Effect of water on the formamide-intercalation of kaolinite

The molecular structures of low defect kaolinite completely intercalated with formamide and formamide-water mixtures have been determined using a combination of X-ray diffraction, thermoanalytical techniques, DRIFT and Raman spectroscopy. Expansion of the kaolinite to 10.09 A was observed with subtle differences whether the kaolinite was expanded with formamide or formamide-water mixtures. Thermal analysis showed that greater amounts of formamide could be intercalated into the kaolinite in the presence of water. New infrared bands were observed for the formamide intercalated kaolinites at 3648, 3630 and 3606 cm(-1). These bands are attributed to the hydroxyl stretching frequencies of the inner surface hydroxyls hydrogen bonded to formamide with water, formamide and interlamellar water. Bands were observed at similar positions in the Raman spectrum. At liquid nitrogen temperature, the 3630 cm(-1) Raman band separated into two bands at 3633 and 3625 cm(-1). DRIFT spectra showed the hydroxyl deformation mode at 905 cm(-1). Changes in the molecular structure of the formamide are observed through both the NH stretching vibrations and the amide 1 and 2 bands. Upon intercalation of kaolinite with formamide, bands are observed at 3460, 3344, 3248 and 3167 cm(-1) attributed to the NH stretching vibration of the NH involved with hydrogen bonded to the oxygens of the kaolinite siloxane surface. In the DRIFT spectra of the formamide intercalated kaolinites bands are observed at 1700 and 1671 cm(-1) and are attributed to the amide 1 and amide 2 vibrations.     

Transverse and longitudinal crystal modes associated with OH stretching vibrations in single crystals of kaolinite and dickite

Raman spectra of randomly-oriented kaolinite, dickite and nacrite show, for coarsely crystalline material, an extra band in the OH stretching region which is absent from the IR spectra of clay-size samples. Oriented single-crystal Raman spectra of these minerals provide confirmation for the assignment of the extra bands to transverse optical modes involving in-phase coupled vibrations of the layer-surface hydroxyl groups. The corresponding IR bands have transition moments nearly perpendicular to the layer surface, and appear at the higher frequencies of the longitudinal optical modes of macroscopic crystals.     

An infrared and Raman spectroscopic study of natural zinc phosphates

Zinc phosphates are important in the study of the phosphatisation of metals. Raman spectroscopy in combination with infrared spectroscopy has been used to characterise the zinc phosphate minerals. The minerals may be characterised by the patterns of the hydroxyl stretching vibrations in both the Raman and infrared spectra. Spencerite is characterised by a sharp Raman band at 3516 cm(-1) and tarbuttite by a single band at 3446 cm(-1). The patterns of the Raman spectra of the hydroxyl stretching region of hopeite and parahopeite are different in line with their differing crystal structures. The Raman spectrum of the PO4 stretching region shows better band separated peaks than the infrared spectra which consist of a complex set of overlapping bands. The position of the PO4 symmetric stretching mode can be used to identify the zinc phosphate mineral. It is apparent that Raman spectroscopy lends itself to the fundamental study of the evolution of zinc phosphate films.     

X-ray diffraction and IR spectral characteristics of zinc(II)tetra-tert-butylphthalocyanine

According to well-known procedures, alpha- and beta-crystal polymorphic modifications of zinc(II)tetra-tert-butylphthalocianine (Zn(t-Bu)4Pc) were prepared and X-ray analysis of their powders was carried out. It was found that four tert-butyl groups in Zn(t-Bu)4Pc molecule do not prevent the formation of the alpha- and beta-polymorphs. The alpha- and beta-polymorphs differ from each other mainly by a mutual arrangement of neighboring metallophthalocyenine molecules in pi-stacking. Comparison of IR spectra of the alpha- and beta-polymorphs of ZnPc and Zn(t-Bu)4Pc was carried out. It was indicated that new bands appear at 670-690, 1256 and 1362 cm(-1) in the spectrum of Zn(t-Bu)4Pc in comparison with that of ZnPc. The appearance of new band at 1256 cm(-1) is assigned to rocking C-CH(3) vibrations and the band at 1362 cm(-1) to symmetrical deformational C-H vibrations of methyl groups of the peripheral substitutes. The main spectral characteristics for identification of the polymorphic modifications of Zn(t-Bu)4Pc are listed.     

Overtone spectroscopy of chlorine substituted benzene derivatives

The absorption spectra of di-, tri- and tetra-derivatives of chlorobenzene have been studied in their pure form in the spectral range 400-20,000 cm(-1). A large number of bands associated with the fundamental, the overtones and the combination frequencies of C-H stretching mode have been observed. Vibrational frequencies, anharmonicity constants and dissociation energies, for the C-H stretch vibrations for the six molecules have been determined using local mode model. The C-H stretch frequencies obtained from experiments are compared with the corresponding frequency determined theoretically using RHF and DFT methods with same 6-31+G* basis set. This information has been used for the assignment of several combination bands as well as some weak overtone bands. Effect of hydrogen atom substitution by chlorine atom has been studied by measuring changes in the vibrational frequency of the C-H stretching mode and the C-H bond length. Frequency changes have been well correlated with the change in charge density on carbon as well as chlorine atoms.     

Polarised IR and Raman spectra of the gamma-glycine single crystal

Complete (full) set of the polarised IR and Raman spectra for the gamma-glycine single crystal at room temperature are presented. The polarised IR spectra were measured by the specular reflection method and the spectra of the imaginary parts of the refractive indices were computed by Kramers-Kronig transformation. The polarised properties of the bands are discussed with respect to the normal coordinate analysis (literature data) and diffraction crystal data (oriented gas model approximation). A very good agreement between the polarised properties of the bands and simple models of vibrations are observed for the stretching vibrations of the CH2 and COO- group. It is not the case for most of the deformation vibrations of the carboxylic group and of the skeleton. The polarization properties of the stretching vibrations of the NH3+ group are determined by their hydrogen bondings.