Intensities Of IR Absorption Bands Research Articles

Isotope Effects in the Spectra of Hydrogen-Bonded Complexes. Calculation of the Structure and Vibrational Absorption Spectra of the H-=SUB=-2-=/SUB=-O...HF, H-=SUB=-2-=/SUB=-O...DF, D-=SUB=-2-=/SUB=-O...HF, and D-=SUB=-2-=/SUB=-O...DF Complexes

The frequencies and intensities of IR absorption bands of the H2O...HF, H2O...DF, D2O...HF, and D2O...DF hydrogen-bonded complexes are calculated using the second-order vibrational perturbation theory. The MP2/aug-cc-pVTZ method with the basis set superposition error taken into account is used to calculate the electronic wave functions in determining the equilibrium configuration, the potential energy and dipole moment surfaces of these complexes, as well as in calculating spectral parameters. It is shown that upon complexation the frequencies and intensities of the stretching vibration of HF (DF) molecules and the intensities of stretching vibrations of H2O (D2O) molecules change most significantly. A variational calculation of librational motion of the water molecule in the two-well potential explained the reason for the higher value of the fundamental transition frequency of the ν1(H-F) mode as compared to the frequency of this mode upon hot transition from the first excited librational state. The dependence of the intermode anharmonic interaction on isotope substitution was analyzed. Keywords: hydrogen bond, calculations of spectra of molecular complexes, anharmonic interactions, isotope effects.

Изотопные эффекты в спектрах комплексов с водородными связями. Ангармонические расчеты изотопологов комплекса [F(HF)-=SUB=-2-=/SUB=-]-=SUP=---=/SUP=-

The frequencies and intensities of IR absorption bands of symmetric and asymmetric H-bonded complexes [FL1FL2F]- (L1, L2 = K-meson Ka, proton H, deuton D, and triton T) are calculated. The equilibrium configuration and potential energy and dipole moment surfaces of isotopologues [FL1FL2F]- were calculated by the MP2/6-311++G(3df,3pd) method with the basis set superposition error taken into account. The calculations of spectral parameters with allowance for anharmonic interactions of all vibrations were carried out using the second-order vibrational perturbation theory. Variation of Li and L2 masses in wide regions allowed significant changes in the forms of normal vibrations and values of anharmonic interaction constants upon isotopic substitution to be obtained. The trends in the changes of spectral parameters were determined upon transition from one symmetric isotopologue to another and upon transition from symmetric to asymmetric isotopologues. The D-F stretching band frequency predicted for [FHFDF]- is in good agreement with the experimental value. The assignment of this band was improved.

Quantum chemical analysis of the molecular structure and vibrational spectrum of arglabin

Results of a theoretical study of the molecular structure of arglabin are pesented. Quantum chemical calculations of the geometry and physicochemical characteristics of arglabin are performed by the semi-empirical PM6 method, the non-empirical Hartree–Fock method, and the hybrid B3LYP DFT method with 6-31G and 6-31G(d) basis sets. By the B3LYP/6-31G(d) method the vibrational frequencies and intensities of IR absorption bands of arglabin are also calculated and the detailed interpretation of the IR spectrum is given. The theoretical frequencies are well consistent with the experimental data.

Calculation of infrared spectra for conformers of a dimeric fragment of the 2,6-hydroxyethylcellulose macromolecule in aqueous solution

Based on both a complete calculation of normal vibration frequencies and absolute IR absorption band inten- sities of a dimeric fragment of the 2,6-hydroxyethylcellulose macromolecule and a comparison of the results with the corresponding experimental data, a detailed interpretation of the IR spectrum (1200-960 cm -1 ) of this polymer is given for the first time. Its conformational characteristics in aqueous solution at 20 and 70 o C were determined by the molecular dynamics method. It is shown that the changes observed in IR spectra of hydroxyethylcellulose in aqueous solutions upon heating may be connected with conformational transitions of the ether side groups. analysis, absolute intensities, spectrum interpretation. Introduction. Water-soluble ethers of cellulose (hydroxyethyl-, carboxymethyl-, methyl-derivatives) are widely used in various industrial sectors. Structural features, in particular, the number and location of ether groups on the pyranose ring and their rotational isomerization are responsible for the valuable properties of these compounds. Vibra- tional spectra (IR and Raman) can reveal even the most subtle structural changes in these macromolcules. Therefore, they are exceedingly effective for studying the structural organization of water-soluble ethers of cellulose (1-4). The reversible changes in the spectra that occur on changing the temperature of the polymers are not related to any chemi- cal transformations in the structure of these compounds and can be explained (5) by a change of the rotational iso- meric (conformational) structure of the macromolecules (6, 7). Studies of the conformational features of the side groups in water-soluble ethers of polysaccharides should establish structureproperty relationships for these practically important compounds. The goal of the present work was to determine the structure of side groups in a dimeric fragment of the water-soluble cellulose ether macromolecule 2,6-hydroxyethylcellulose (2,6-HEC) in aqueous solution at various tem- peratures, to calculate the frequencies and potential energy distribution (PED) of normal vibrations and absolute inten- sities of IR absorption bands, and to model the optical density spectrum of the most stable conformers of the ether groups of this fragment. Experimental Method. The stated problem was solved using a combined approach (8) to modeling IR spec- tra of organic compounds that used both molecular mechanics and quantum chemistry methods to calculate the fre- quencies of normal vibrations and absolute intensities of IR absorption bands, respectively, of polyatomic molecules. The algorithm for calculating the absolute intensities within the framework of the applied approach (as for using the valence force field approximation (8, 9)) consisted of calculating the derivatives of the electron-density P matrix over Decartes shifts of atoms and the matrix of derivatives ∂r ⁄ ∂Qi from Decartes shifts of atoms over normal coordinates and multiplying the resulting matrices. Shifts of atoms in Decartes coordinates in each normal vibration were calcu- lated using molecular mechanics (solution of the direct spectral problem). Matrices of charges on atomic nuclei, elec- tron densities, and bond orders were calculated using the CNDO/2 quantum-chemical method. The derivatives of these

Theoretical analysis of the IR spectrum of methyl-3,4-anhydro-α-D-talohexopyranoside

A detailed interpretation of the IR spectrum of methyl-3,4-anhydro-α-D-talohexopyranoside that is based on complete calculation of normal vibration frequencies and absolute IR absorption band intensities of the molecule and a comparison of the results obtained with the corresponding experimental data is given for the first time. The influence of the epoxy group on the absorption bands characteristic of the pyranose ring has been analyzed.

Interpretation of the IR spectrum of methyl-β-D-glucopyranoside based on the theoretical calculation of frequencies and intensities of normal vibrations

For the first time the detailed interpretation of the IR spectrum of methyl-β-D-glucopyranoside is presented based on the complete calculation of frequencies of normal vibrations and absolute intensities of IR absorption bands and on their comparison with the corresponding experimental values. The characteristic spectral features of oxymethyl substitution for the hydroxyl group are detected. The regularities in the formation of the complex band structure in a frequency range from 1150 cm−1 to 950 cm−1 is determined.

The effect of electron irradiation on the optical properties of the natural armenian zeolite-clinoptilolite

Abstract Infrared (IR) absorption and luminescence in chemically and radiation-modified natural Armenian Zeolite (clinoptilolite) samples have been studied. The luminescence was studied in 390–450 nm and 620–710 nm wavelength bands, and the IR measurements were carried out in the 400–5400 cm−1 range. It is shown that the luminescence intensity depends on the content of pure clinoptilolite in the samples and, probably on the distribution of “passive” luminescence centers over Si and Al sites that became “active” under radiation or chemical treatment. The samples of electron irradiated clinoptilolite have higher luminescence intensity than the chemically and thermally treated ones. A decrease in the intensity of IR absorption bands at 3550 cm−1 and 3650 cm−1 was found after irradiation.

Quantum-Chemical Study of Ion Association in Electrolyte Systems Containing LiAsF6

The possibility that ion clusters of different species are formed during dissolution of LiAsF6 in a low- or high-molecular-weight solvent has been studied. The Hessian matrix of clusters has been calculated by the numerical and analytical differentiation of their full energy in the MO LCAO approximation using the Roothaan−Hartree−Fock method and the PC GAMESS software package. It was found that stable ion clusters are represented by ion pairs Li+[AsF6]- with the bi- or tridentate coordination of the cation relative to the octahedral anion, triple ions [AsF6]-Li+[AsF6]- and Li+[AsF6]-Li+ with the bi- or tridentate coordination, ion dimers {Li+[AsF6]-}2 with the bidentate coordination, and also ion trimers {Li+[AsF6]-}3 and ion tetramers {Li+[AsF6]-}4 shaped as symmetric ring structures with the unidentate coordination. The frequencies and intensities of IR absorption bands of different species of ion clusters in the gaseous phase and nonaqueous solutions (acetone, ethanol, nitromethane, and tetrahydrofurane) have been calculated. This presents a basis for identification of ion particles during IR spectroscopic measurements in electrolyte solutions containing LiAsF6.

Blackbody Infrared Radiative Dissociation of Partially Solvated Mixed Ligand Ru(II) Complex Ions

Unimolecular dissociation reactions of gas-phase partially solvated transition metal complex ions, diamminebis(2,2‘-bipyridine)ruthenium(II), [Ru(NH3)2(bipy)2]2+, tetraammine(2,2‘-bipyridine)ruthenium(II), [Ru(NH3)4bipy]2+, and pentaammine(2-methylpyrazine)ruthenium(II), [Ru(NH3)5MePyz]3+, have been investigated with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI−FTICR/MS) under low pressure (<10-8 mbar) conditions. Under these conditions, dissociation of solvent from the complex ions is driven primarily by absorption of blackbody photons from the FTICR analyzer cell walls, that is, via blackbody infrared radiative dissociation (BIRD), with little collisional contribution at pressures below 10-8 mbar. The replacement of ammine hydrogens with deuterium increases measured BIRD rate constants. Optimized geometries, vibrational frequencies, and IR absorption band intensities have been calculated for the complexes by semiempirical and ab initio methods. These calculated parameters have been employed in master equation modeling of the desolvation reactions to extract dissociation energetics. Solvation energies obtained by master equation modeling were found to be in the range 19 ± 1 kcal/mol for the dissociation of acetone from various mixed ligand Ru(II) complex ions studied in this work. This is about 4 kcal/mol higher than for the comparable complexes containing only bipyridyl ligands and no ammine ligands.

Study of 1,5,7-triazabicyclo[4,4,0]dec-5-ene protonation by vibrational spectroscopic methods

The normal coordinate analysis and calculation of the IR absorption band intensities have been carried out for 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) and its three possible protonated tautomeric forms. It has been shown that protonated molecule TBD has only one tautomeric species in which proton is attached to imine nitrogen atom.

Thermal and Spectroscopic Characterization of Interactions between 2-Nonyl-1,3-Dioxolane and Stratum Corneum Components

The effect of 2-nonyl-1,3-dioxolane (SEPA™) on the structure of human stratum corneum was investigated by FT-IR spectroscopy at variable temperature, differential scanning calorimetry and scanning electron microscopy. A significant influence of SEPA™ treatment on position and intensity of IR absorption bands and DSC thermal transitions of SC lipids was detected. An appreciable loosening of SC cell packing was also observed by SEM analysis. These modifications are reversed after SEPA™ is removed from the site of application. The results clearly demonstrate that SEPA™ is able to modify the structure of the lipid matrix in which corneocytes are embedded, thus suggesting a possible use of SEPA™ to increase the permeability of the stratum corneum to lipophilic drugs.

Grinding effects of host crystals on formation and properties of titania pillared fluorine micas

Fluorine micas having different grinding times were allowed to react with titania sol prepared by hydrolyzing titanium tetraisopropoxide (TTIP) with hydrochloric acid in order to clarify the influence of grinding upon reactivity of synthetic fluorine micas [M0.8Mg2.2Li0.8(Si4O10)F2(M = Na, Li)]. Prolongation of grinding time promoted delamination and fineness of host mica crystals, resulting in increasing specific surface area. The heating weight loss and intensity of IR absorption bands around 1600 and 3400 cm−1 also increased with increasing grinding time, indicating the increase in absorbed water on ground mica particles. Properties of titania pillared fluorine micas depended on grinding time of host micas. Specific surface areas and titania contents of pillared fluorine micas increased with increasing grinding time, so that the effect of interlayer cations (Na+, Li+) upon complex formation of titania pillared micas almost diminished. When host mica crystals were larger, the reaction occurred mainly in the interlayer region. However, when host mica crystals were ground to be finer, the reaction on external surfaces of ground particles occurred simultaneously along with intercalation. These results show that mechanochemical effects resulted from grinding have the profound influence on the formation and properties of titania pillared fluorine micas.

ＣａＯ‐Ｂ２Ｏ３‐Ｈ２Ｏ系ホウ酸塩鉱物 特に岡山県備中町有賀産の例について

Calcium-borate minerals such as takedaite and parasibirskite have been found in a vein in crystalline limestone near gehlenite-spurrite skarns at Fuka, Okayama Prefecture, Japan. The minerals are plotted in the CaO:B2O3 molar ratio range from 1 : 1 to 3 : 1 and up to 0.25 in the B2O3 ratio in the CaO-B2O3-H2O system. This paper reviews the author's studies on physical and chemical properties and genesis of the borate minerals. The properties show the following characteristics with an increase of water content in the minerals: (1) the refractive indices, birefringence, hardness and density of the minerals decrease; (2) the endothermic peaks on the DTA curve shift remarkably at low temperature; (3) the intensity of IR absorption bands near 3400 cm-1 increases, and the band near 1000 cm-1 shifts toward the lower frequency region. The formation of the minerals may be considered as follows: (1) takedaite was primarily formed by a reaction of boron-bearing fluids with limestone; (2) sibirskite and parasibirskite were formed by hydrothermal alteration of takedaite; (3) a late-hydrothermal solution converted sibirskite and parasibirskite to olshanskyite, frolovite and nifontovite.

Products of the gas-phase reaction of the OH radical with 3-methyl-1-butene in the presence of NO

The products of the gas-phase reaction of the OH radical with 3-methyl-1-butene in the presence of NO have been investigated at room temperature and 740 torr total pressure of air by gas chromatography with flame ionization detection, in situ Fourier transform infrared absorption spectroscopy, and direct air sampling atmospheric pressure ionization tandem mass spectrometry. The products identified and quantified by GC-FID and in situ FT-IR absorption spectroscopy were HCHO, 2-methylpropanal, acetone, glycolaldehyde, and methacrolein, with formation yields of 0.70±0.06, 0.58±0.08, 0.17±0.02, 0.18±0.03, and 0.033±0.007, respectively. In addition, IR absorption bands due to organic nitrates were observed, consistent with API-MS observations of product ion peaks attributed to the β-hydroxynitrates (CH3)2CHCH(ONO2)CH2OH and/or (CH3)2CHCH(OH)CH2ONO2 formed from the reactions of the corresponding β-hydroxyalkyl peroxy radicals with NO. A formation yield of ca. 0.15 for these nitrates was estimated using IR absorption band intensities for known organic nitrates. These products account for essentially all of the reacted 3-methyl-1-butene. Analysis of the potential reaction pathways involved shows that H-atom abstraction from the allylic C(SINGLEBOND)H bond in 3-methyl-1-butene is a minor pathway which accounts for 5–10% of the overall OH radical reaction. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 577–587, 1998

Relation between the intensity of ir absorption bands of stretching vibrations of nitrogroups and their number in aromatic nitrocompounds

Relation between the intensity of ir absorption bands of stretching vibrations of nitrogroups and their number in aromatic nitrocompounds

Determination of ion association constants by means of IR absorption band intensities of the molecules forming the first coordination spheres of the cations

Abstract The IR spectra of the binary systems CH 3 CNLiI, CH 3 CNLiClO 4 and CH 3 CNLiNCS in the regions of the stretching vibrations of CC and CN bonds of acetonitrile have been recorded. The association constants have been determined on the basis of the analysis of the IR absorption band intensities of acetonitrile molecules. The values of the absorption coefficients of the molecules forming the first coordination spheres of Li + cations have been estimated.

Saturated aldehyde series

In this article we examine results obtained in a direct quantum calculation (based on the semiempirical MINDO/3 method) of the electrooptical parameters (EOPs) and the optimized molecular geometry of a series of saturated aldehydes: formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and valeraldehyde. The quantum calculation was performed in a system of dependent natural coordinates. The EOPs of the molecules were found within the framework of a valence—optical scheme and have been used in solving problems of determining intensities of IR absorption bands. Theoretical and experimental curves have been compared.

Integral intensities of IR absorption bands of symmetric vibration of a ring and intramolecular interactions in 3-substituted derivatives of cyclopropene

Integral intensities of IR absorption bands of symmetric vibration of a ring and intramolecular interactions in 3-substituted derivatives of cyclopropene

Calculation of absorption band frequencies and intensities in the IR spectrum of α- d-glucose in a cluster

Coupled calculations of the vibrational frequencies and intensities of IR absorption bands of α- d-glucose have been performed taking into account the influence of intermolecular hydrogen bonds in a crystal on the intensity of the molecular absorption bands. The analysis of normal vibrations was carried out in the framework of the valence force field. The intensities were calculated by the quantum-chemical technique CNDO/2. The calculations of the α- d-glucose IR spectra were performed in two approximations: a quasi-isolated molecule (QIM) and a molecule in a cluster. As the QIM approximation, a 24-atom isolated molecule is considered. The average influence of intermolecular interactions is taken into account only in the molecule's field of forces. As the second approximation, an 84-atom cluster model of crystalline α- d-glucose is considered, which permits one to take into account the influence of intermolecular hydrogen bonds in the crystal on the electronic structure of the molecule in calculating the intensities. A detailed interpretation of the observable spectrum is given. A high sensitivity of band intensities of OH-valence vibrations in the 3600-3000 cm −1 region to the formation of hydrogen bonds and a marked sensitivity in the 600-450 cm −1 region is shown. It is found that the IR spectra of monosaccharides in the 3000-600 cm −1 range can be interpreted in the quasi-isolated molecule approximation.

FT–IR spectroscopic study on the thermal and thermal oxidative degradation of nylons

AbstractThe effects of heat and oxygen on nylon films were studied by FT–IR spectroscopy. Nylons 6, 66 and nylons containing carbonyl groups in either the diamine or the diacid moiety were prepared. Nylon films cast on aluminum were studied in an environmental chamber under controlled conditions. The progress of chemical and physical changes was monitored by FT–IR spectroscopy. Thermal energy caused largely an increase in crystallinity due to annealing and also an increase of nonhydrogen‐bonded amide groups, which seemed to entail mainly amide groups from the amorphous region. The intensities of IR absorption bands related to the folded structure reduced as soon as heating began. The IR spectra of the carbonyl groups formed by thermal oxidation showed band shapes that indicated that the formed carbonyl groups were of many different origins. The presence of keto groups purposely inserted into the backbone chains increased the rate of oxidation. Pyrolysis of the nylons was also studied to supplement data obtained at lower temperatures.