Intensity Of Vibrational Bands Research Articles

FT-Raman, FT-IR, UV spectra and DFT and ab initio calculations on monomeric and dimeric structures of 3,5-pyridinedicarboxylic acid

The FT-IR and FT-Raman spectra of 3,5-pyridinedicarboxylic acid (dinicotinic acid, C7H5NO4) in the solid phase were recorded. The fundamental vibrational wavenumbers, intensities of vibrational bands and the optimized geometrical parameters of the compound are evaluated using HF and DFT (B3LYP) methods with 6-311G(d) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The computed dimer parameters also show agreement with experimental data. The complete assignments were performed on the basis of the total energy distribution (TED). Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. UV–visible spectrum of the compound was recorded in the region 200–400nm and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures were calculated.

Protein Adsorption at the Electrified Air–Water Interface: Implications on Foam Stability

The surface chemistry of ions, water molecules, and proteins as well as their ability to form stable networks in foams can influence and control macroscopic properties such as taste and texture of dairy products considerably. Despite the significant relevance of protein adsorption at liquid interfaces, a molecular level understanding on the arrangement of proteins at interfaces and their interactions has been elusive. Therefore, we have addressed the adsorption of the model protein bovine serum albumin (BSA) at the air-water interface with vibrational sum-frequency generation (SFG) and ellipsometry. SFG provides specific information on the composition and average orientation of molecules at interfaces, while complementary information on the thickness of the adsorbed layer can be obtained with ellipsometry. Adsorption of charged BSA proteins at the water surface leads to an electrified interface, pH dependent charging, and electric field-induced polar ordering of interfacial H(2)O and BSA. Varying the bulk pH of protein solutions changes the intensities of the protein related vibrational bands substantially, while dramatic changes in vibrational bands of interfacial H(2)O are simultaneously observed. These observations have allowed us to determine the isoelectric point of BSA directly at the electrolyte-air interface for the first time. BSA covered air-water interfaces with a pH near the isoelectric point form an amorphous network of possibly agglomerated BSA proteins. Finally, we provide a direct correlation of the molecular structure of BSA interfaces with foam stability and new information on the link between microscopic properties of BSA at water surfaces and macroscopic properties such as the stability of protein foams.

Comparison Between Conventional Convective Heating and Microwave Heating: An FTIR Spectroscopy Study of the Effects of Microwave Oven Cooking of Bovine Breast Meat

The effects of microwave energy and conventional convective heating on bovine meat were studied in the mid-infrared region by FTIR spectroscopy, to highlight the differences between the two cooking methods. Samples of 100 g of bovine breast meat were cooked using three treatments: heating in a conventional electric oven at the temperature of 165°C for 16 min, heating in a microwave oven at 800 W for 95 sec, and heating in the same microwave oven at 650 W for 160 sec. Significant decreases in intensity of vibration bands of CH2 methylene group at 1921 and 1853 cm-1 and of the carbonyl band at 1742 cm-1 were observed after microwave heating with respect to heating in a conventional oven, showing that Maillard reaction occurs partially using microwave oven. Spectral analysis in the amide I region after microwave cooking at 800 W for 95 sec showed that an increase in intensity occurred in the region from 1665 to 1690 cm-1 which can be attributed to β-turns, characteristic of disorder processes in the protein. Further analysis after microwave cooking at 650 W for 160 sec evidenced major increase in intensity of β-turns content and the appearance of significant increases of β-sheet component at 1635 cm-1 and 1695 cm-1 that can be attributed to aggregated β-sheets structures.

Synthesis and characterization of silver/silicon‐cosubstituted nanohydroxyapatite

Favorable cell-material interaction and the absence of undesirable reaction from the host body defence system play a critical role in determining the success and long-term survival of the implants. Substitution of various elements into hydroxyapatite (HA) has been done to alter its chemical composition, thereby mimicking that of the bone mineral. In this study, a cosubstituted nanosized apatite (Ag/Si-HA) containing Ag (0.3 wt %) and Si (0.8 wt %) was synthesized by an aqueous precipitation technique. The synthesized Ag/Si-HA displayed a rod-like morphology of dimensions ~50 nm in length and ~15 nm in width, as observed from the transmission electron microscope image. With an increase in temperature, the aspect ratio of nanosized Ag/Si-HA decreased, whilst the size increased. Autoclaving was used to achieve sufficient crystallinity while maintaining the rod-like morphology and size that were comparable to that of the bone apatite. A pure Ag/Si-HA was produced without any undesirable secondary phases, as evidenced from the X-ray diffraction and thermal gravimetric results. The Ag/Si cosubstitution affected the lattice cell parameters, in particularly the a- and c- axes which further led to an expansion of the unit cell volume. In addition, the relative intensity of the hydroxyl vibrational bands was reduced. These results demonstrated that a stable phase-pure Ag/Si-HA was produced using an aqueous precipitation reaction.

Unraveling Tryptophan Modulated 2D DPPC Lattices: An Approach toward Stimuli Responsiveness of the Pulmonary Surfactant

A molecular understanding on the preferential and selective interactions of L-tryptophan, a major component of surfactant proteins, with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) is important in the metabolic cycle of the pulmonary surfactant. In view of this, interfacial signals of interest in real time were tapped with aligned DPPC monolayers over a physiological tryptophan subphase using extremely surface sensitive 2D vibrational spectroscopy. Polarization-modulated and angle dependent Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) of DPPC monolayers on water and L-tryptophan subphases depicted fine structure/conformation differences in the interaction modes, evidenced from changes in the vibrational band intensities and frequencies under conditions of controlled 2D surface pressure. The computed 1:1 adducts of DPPC/H(2)O and DPPC/tryptophan in support of FT-IRRAS fine structure characteristics demonstrated binding in interfacial DPPC-tryptophan adducts to be driven by cation-π interactions alongside hydrogen bonding of carbonyl and phosphate groups of the lipid with NH(3)(+) of the zwitterionic tryptophan. In situ spectroscopy enabled assignment of relative orientations of the equivalent -CH(2) functional groups from the polarized XY plane transition moments with component intensities of the split orthorhombic CH(2) mode. A larger molecular tilt of 37° for the DPPC monolayer over tryptophan subphase in comparison with that over water (26°) substantiated the DPPC headgroup interaction with tryptophan, complemented through δ (N(+)(CH(3))(3)), ν(as) (PO(2)(-)), ν(s) (PO(2)(-)), ν(as) (C-N(+)-C), and ν (C═O) vibrational features. The IRRAS spectral features of the DPPC 2D condensed phase showed distinct tryptophan-induced temperature dependent lattice phase transitions: hexagonal → orthorhombic → triclinic → hexagonal packing of the hydrocarbon chains was noted over a subphase temperature range from 20 to 43 °C. The temperature dependent 2D DPPC lattice characteristics cited in this work will aid in understanding the impact of a temperature pulse toward the membrane functionality.

Low temperature cavity ring down spectroscopy with off-axis alignment: application to the A- and γ-bands of O2 in the visible at 90 K

The cavity ring down (CRD) technique presented here involves an optical cavity attached to a cryostat. The static cell and mirrors of the optical cavity are all inside a vacuum chamber at the same temperature of the cryostat. The temperature of the cell can be changed between 77 K and 298 K. An off-axis alignment of the laser beam into the cavity is used to increase the number of resonant modes inside the cavity and improve the signal to noise ratio of the absorption bands. To demonstrate the capabilities of the low temperature CRD cell, the absorption spectra of O2 are recorded at 90 K for the A (υ′=0←υ″=0) and γ (υ′=2←υ″=0) bands of the \(b^{1}\sum_{g}^{ +}\leftarrow X^{3}\sum_{g}^{ -} \) transition using cavity ring down spectroscopy. The optical cavity performance was tested using two variations of the CRD technique. The A-band is measured using the phase-shift cavity ring down method and the γ-band using the pulsed-laser exponential-decay method. A comparison between experimental and simulated spectra of the O2 bands at 90 K confirms the molecular temperature measured by a sensor localized in the cell. Quantitative measurements of the individual rotational line intensities are made for the oxygen γ-band to confirm the temperature of the cell and calculate the vibrational band intensity. The application of this technique for laboratory studies of planetary atmospheres and the spectroscopy of molecular complexes is emphasized.

Vibrational investigation, molecular orbital studies and molecular electrostatic potential map analysis on 3-chlorobenzoic acid using hybrid computational calculations

The FT-IR and FT-Raman spectra of 3-chlorobenzoic acid (3CBA) are recorded in the liquid state. The fundamental vibrational frequencies, intensity of vibrational bands and the optimized geometrical parameters of the compound are evaluated using HF and DFT (LSDA/B3LYP/B3PW91/MPW1PW91) methods with 6-311+G(d,p) basis set. The theoretical wave numbers are scaled down and compared with the experimental values which showed very good agreement. Comparison of stimulated spectra with the experimental spectra provides important information about the ability of the hybrid computational method to describe the vibrational modes. The HOMO, LUMO, chemical hardness ( η), chemical potential ( μ), electrophilicity values ( ω) and maximum amount of electronic charge transfer (Δ N max) are calculated. The molecular electrostatic potential (MESP) is calculated and the corresponding graphs are drawn. Some thermodynamic parameters and physico-chemical properties are calculated and discussed.

A Simple Method for Obtaining the Information of Orientation Distribution Using Polarized Raman Spectroscopy: Orientation Study of Structural Units in Poly(lactic acid)

A simple approach using polarized Raman spectroscopy has been employed to study the molecular orientation distribution in both the crystalline and amorphous regions of uniaxially oriented poly(l-lactic acid) (PLLA) films. The effect of morphology on the intensity of the Raman bands was evaluated to provide qualitative information on the distributions of the crystalline and amorphous regions to the peak intensities. The angular dependence of the scattered intensity of assignable vibration bands was analyzed to quantify the orientation degree of the symmetry axis of Raman tensors. The results showed that the measurement of polarization of scattered intensity as a function of rotating angle can provide semiqualitative information on the shape of the orientation distribution function. On the basis of the results, orientational variation of both amorphous and crystalline chains can be described under the deformation of film and compared with previous studies.

Surface Complexation of 2,5-Dihydroxybenzoic Acid (Gentisic Acid) at the Nanosized Hematite−Water Interface: An ATR-FTIR Study and Modeling Approach

In this study, characteristic interactions of 2,5-dihydroxybenzoic acid (or gentisic acid, GA) with the surface of 15-nm-sized hematite (α-Fe2O3) were studied by combining batch macroscopic experiments, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic investigations, and surface complexation modeling. A correlation between the pH, the amount of adsorbed GA, and the amount of Fe(III) released from the hematite surface was observed, whereas the dissolution of hematite nanoparticles became significant only at low pH and high ligand loading. From the ATR-FTIR results, two aqueous complex structures have been identified depending on pH. At the hematite-water interface, the occurrence of one deprotonated inner-sphere "bidentate" complex and one outer-sphere complex was suggested through all of the investigated pH range. At high surface coverage, variations of vibrational band intensities were observed, suggesting the occurrence of nonspecific molecular interactions. The macroscopic results (i.e., GA batch sorption and the ligand-promoted dissolution of hematite) obtained under a wide range of experimental conditions corroborated the ATR-FTIR microscopic findings. GA adsorption was described by a surface complexation model fitted to pH-adsorption curves with 1 mM sorbate concentration in the pH range of 3-9. Two surface complexes (one outer-sphere species (≡FeOH2)2···H2L((1+,1-)) and one inner-sphere species (≡Fe)2H2L) were proposed using the three-plane model. The inner-sphere complexes were predominant at low pH values, and the relative concentrations of the outer-sphere species increased with the pH increase. The formation of inner-sphere complexes at acidic pH values can promote the dissolution of nanosized hematite. At high solute loading, GA oxidation into carboxybenzoquinone compounds by ferric species was suspected, suggesting the occurrence of a redox reaction analogous to that of hydroquinone compounds.

Strong and weak effects caused by non covalent interactions between chloroform and selected electron donor molecules

The FTIR spectra of chloroform (Cl(3)CH) in mixtures with various electron donors (B = CH(3)CCH, HCCH, NCCD(3), ClCD(3) and CO) have been studied in liquefied Kr. Spectroscopic evidence of weak H-bond formation has been found. The relative stability of some complexes has been evaluated from temperature studies of integrated intensities of vibrational bands attributed to monomer and complex species. A weak red shift of the stretching vibration of chloroform involved in H-bonding with CH(3)CCH and HCCH having π-electron area was observed. However, in the case of interactions with NCCD(3) and CO, a weak blue shift was detected. In most of the cases, a noticeable increase in the integrated intensity of the CH stretching band was found. Ab initio MP2/6-311++G(2d,2p) a priori counterpoise corrected calculations have been performed for a series of Cl(3)CH and B. Stationary points at the potential energy surface were examined and the structures related to the real minima have been found. The calculations reproduce the majority of experimental results. It has been found that the commonly used correlation between the frequency shift of the CH stretching vibration of the proton donor subunit and the change in CH bond length can fail in the case of the complexes characterized by a weak frequency shift effect.

Mechanism of enhancement in absorbance of vibrational bands of adsorbates at a metal mesh with subwavelength hole arrays

We have investigated the mechanism of enhanced absorption intensities of vibrational bands of adsorbates on copper meshes with subwavelength holes by measuring and simulating temporal profiles of infrared pulses transmitted through the meshes. As reported previously [Williams et al., J. Phys. Chem. B, 2003, 107, 11871], the absorption intensities of CH stretching bands of alkanethiolate adsorbed on the mesh increase substantially with decreasing hole size. The enhancements of absorption intensities are associated with temporal delays of infrared pulses transmitted through the mesh. Finite difference time domain calculations reproduce the observed pulse delays as a function of hole size. These facts indicate that the delays of transmitted pulses are not caused by coupling of infrared radiation to surface plasmon polaritons propagating on the front and rear surfaces of the mesh, but they are caused by the reduction in group velocity owing to coupling to waveguide modes of mesh holes. Consequently, the strong enhancements of the absorption intensities are attributed to adsorbates inside the holes rather than to those on the mesh surfaces that have been proposed previously.

Influence of the pH on the Surface and Optical Properties of the Thin Film of Polyaniline / Polyethylene Terephthalate Composite. The AFM and Spectroscopies Studies

ABSTRACTThe effect of pH was investigated on the morphological and spectroscopic properties of PANI thin films on PET. PANI/PET strips were prepared by a pattern-printing technique and coated with a thin film of polyaniline in situ emeraldine oxidation state, doped with HCl (PANI-HCl), obtained by in situ polymerization. AFM, UV-VIS-NIR and FTIR/ATR spectroscopic results showed that pH has a great influence on the polymer layer morphology of the coating layers, while the intensity of vibrational bands decreases with rising pH, increase due to changes in the H-bonded structure in the polymer chain.

Cryospectroscopic and ab initio anharmonic studies of acetylene–trimethylamine H-bonded complex

The FTIR spectra of C 2H 2 in mixtures with trimethylamine (TMA) have been studied in liquefied Kr in the frequency range of ∼800–7000 cm −1. The data obtained for C 2H 2 subunit suggest the formation of 1:1 complexes stabilized by a moderate strength conventional H-bond. CH and CN stretching vibrations, related to the vicinal bonds of proton acceptor, were found to shift in opposite directions – blue in the former and red in the latter case. New weak bands, revealed in the range of ∼6000–7000 cm −1, were ascribed to the overtone and combination bands of C H stretching vibrations of acetylene which participates in the H-bond formation. The relative stability of the complex has been determined in a series of temperature ( T = 118–157 K) measurements of integrated intensities of vibrational bands ascribed to monomer and complex species. Ab initio MP2/6-311++G(2d,2p) a priory counterpoise corrected calculations, made for acetylene, TMA, and the complex reproduce the main spectroscopic observations. They suggest that the most stable non-linear structure of the complex is very floppy. Evaluations of anharmonic effects on position and integrated intensity of selected bands of C H stretching modes of C 2H 2 subunit have been made within perturbation theory on the basis of single point potential energy surface (PES) and dipole moment function calculations.

Ro-vibrational spectra of C2H2 based on variational nuclear motion calculations

A published ab initio-based potential energy surface and newly constructed dipole moment surface of acetylene have been used to compute vibrational band intensities. The line intensity calculations employed the variational nuclear motion code WAVR4 for computation of wave functions and energy levels, and a newly developed code DIPOLE4 for computation of dipole transitions. Owing to the high computational cost of J > 0 transitions using direct variational methods only J = 0 and J = 1 states and transitions have been computed variationally. The intensities of J > 1 transitions were extrapolated from J = 0 and J = 1 using Hönl–London coefficients. The resulting effective rotational constants B and transition intensities are compared with experimental data for the (3ν4 + ν5) combination band, the ν3 and the ν5 fundamental band. The prospects of using this procedure for extensive calculations of a hot line list, important for cool stars and extrasolar planets are discussed.

Electrical conductivity and dielectric behaviour of PPG4–AgCF3SO3:Al2O3 nanocomposite gel polymer electrolyte system

In this report, the synthesis of solvent-free poly(propylene glycol) 4000 (PPG4)–silver triflate (AgCF3SO3):xAl2O3 nanocomposite gel polymer electrolytes containing four different amounts of Al2O3 nanoparticles corresponding to x = 1, 3, 5 and 7 wt.%, respectively, with an ether oxygen-to-metal cation ratio (O–M) of 4:1 together with their vibrational spectroscopic characteristics derived from Fourier transform infrared (FT-IR ) spectroscopic analysis at room temperature (25 °C) is described. Furthermore, a detailed investigation concerning their mechanism of ion transport performed by means of complex impedance analysis in the frequency range 20 Hz to 1 MHz and over the temperature region 25–90 °C and analysed in terms of electrical conductivity spectra, electrical modulus spectra and impedance spectra has indicated that the typical composition PPG4–AgCF3SO3:5 wt.% Al2O3 would exhibit the best room temperature electrical conductivity of 6.2 × 10−4 S cm−1 owing to the mobility of coordinated silver cations through the mechanism of enhanced segmental motion of the PPG4 polymer chains as aided by the various coordinating sites available within the polymer network. It is also demonstrated from the present FT-IR results that significant changes in the intensity, shape and position of the different vibrational bands corresponding to –OH stretching, C–O–C stretching, C–H stretching and C–O–C in C–H stretching modes occur as a result of the incorporation of Al2O3 nanofiller particles into the PPG4–AgCF3SO3 complex. It is evident from the conductivity data that the observed enhancement in electrical conductivity would result from appropriate changes in ionic association occurring in the form of probable ion–ion and ion–polymer interactions involving Al2O3 nanofiller additive in accordance with the Lewis acid–base model of polymer–salt–filler interactions.

Structure and vibrational frequencies of 6,7-dimethoxy-1,4-dihydro-1,3-quinoxalinedione based on density functional theory calculations: The role of π-electron conjugation and back-donation

This work deals with the vibrational spectroscopy of 6,7-dimethoxy-1,4-dihydro-1,3-quinoxalinedione by means of quantum chemical calculations. The mid and far FT-IR and FT-Raman spectra are recorded in the condensed State. The fundamental vibrational frequencies and intensity of vibrational bands are evaluated using density functional theory (DFT) with the standard B3LYP/6-31G* method and basis set combination and is scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectrum is interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results of the calculations are applied to simulate infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. The infrared unscaled frequencies and intensities are used to disentangle the role played by back-donation in the title compound. For this purpose five other molecules are considered as references: ethane, dimethyl ether, anisole, p-nitro-anisole, and p-hydroxyanisole, in which back-donation has already been ascertained also experimentally. From the study of infrared intensities it is shown that no back-donation of electrons from the oxygen lone pairs takes place, independently of the conformation of the methoxy-group.

N -alkane adsorption to polar silica surfaces

The structures of medium-length n-alkane species (C(8)-C(11)) adsorbed to a hydrophilic silica/vapor interface were examined using vibrational sum frequency spectroscopy. Experiments sampling out-of-plane orientation show a clear pattern in vibrational band intensities that implies chains having primarily all-trans conformations lying flat along the interface. Further analysis shows that the methylene groups of the alkane chains have their local symmetry axes directed into and away from the surface. Spectra acquired under different polarization conditions interlock to reinforce this picture of interfacial structure and organization. Variation in signal intensities with chain length suggests that correlation between adsorbed monomers weakens with increasing chain length. This result stands in contrast with alkane behavior at neat liquid/vapor interfaces where longer length alkanes show considerably more surface induced ordering than short chain alkanes.

Vibrational dynamics of metal cyanides

Time-resolved IR spectroscopy has been used to characterize vibrational and rotational relaxation dynamics of the C–N stretching bands for aqueous molecular cyanides, Au ( CN ) 2 - , Ni ( CN ) 4 2 - , Pt ( CN ) 4 2 - , Co ( CN ) 6 3 - , Mn ( CN ) 6 3 - , and Ru ( CN ) 6 4 - . The spectra and dynamics of Ru ( CN ) 6 4 - resemble those previously reported for ferrocyanide with a relatively short (<10 ps) vibrational energy relaxation (VER) time. VER times are longer (>30 ps) for Au ( CN ) 2 - , Ni ( CN ) 4 2 - , Pt ( CN ) 4 2 - and Co ( CN ) 6 3 - . Mn ( CN ) 6 3 - is an intermediate case with a VER time of 15 ps in water. These VER dynamics extend and reinforce the trends for metal cyanide CN vibrational band frequencies and intensities.

First-principles prediction and partial characterization of the vibrational states of water up to dissociation

A new, accurate, global, mass-independent, first-principles potential energy surface (PES) is presented for the ground electronic state of the water molecule. The PES is based on 2200 energy points computed at the all-electron aug-cc-pCV6Z IC-MRCI(8,2) level of electronic structure theory and includes the relativistic one-electron mass-velocity and Darwin corrections. For H 2 16O, the PES has a dissociation energy of D 0 = 41 109 cm −1 and supports 1150 vibrational energy levels up to 41 083 cm −1. The deviation between the computed and the experimentally measured energy levels is below 15 cm −1 for all the states with energies less than 39 000 cm −1. Characterization of approximate vibrational quantum numbers is performed using several techniques: energy decomposition, wave function plots, normal mode distribution, expectation values of the squares of internal coordinates, and perturbing the bending part of the PES. Vibrational normal mode labels, though often not physically meaningful, have been assigned to all the states below 26 500 cm −1 and to many more above it, including some highly excited stretching states all the way to dissociation. Issues to do with calculating vibrational band intensities for the higher-lying states are discussed.

Communications: Infrared spectroscopy of gas phase C3H3+ ions: The cyclopropenyl and propargyl cations

C(3)H(3)(+) ions produced with a pulsed discharge source and cooled in a supersonic beam are studied with infrared laser photodissociation spectroscopy in the 800-4000 cm(-1) region using the rare gas tagging method. Vibrational bands in the C-H stretching and fingerprint regions confirm the presence of both the cyclopropenyl and propargyl cations. Because there is a high barrier separating these two structures, they are presumed to be produced by different routes in the plasma chemistry; their relative abundance can be adjusted by varying the ion source conditions. Prominent features for the cyclopropenyl species include the asymmetric carbon stretch (nu(5)) at 1293 cm(-1) and the asymmetric C-H stretch (nu(4)) at 3182 cm(-1), whereas propargyl has the CH(2) scissors (nu(4)) at 1445, the C-C triple bond stretch (nu(3)) at 2077 and three C-H stretches (nu(2), nu(9), and nu(1)) at 3004, 3093, and 3238 cm(-1). Density functional theory computations of vibrational spectra for the two isomeric ions with and without the argon tag reproduce the experimental features qualitatively; according to theory the tag atom only perturbs the spectra slightly. Although these data confirm the accepted structural pictures of the cyclopropenyl and propargyl cations, close agreement between theoretical predictions and the measured vibrational band positions and intensities cannot be obtained. Band intensities are influenced by the energy dependence and dynamics of photodissociation, but there appear to be fundamental problems in computed band positions independent of the level of theory employed. These new data provide infrared signatures in the fingerprint region for these prototypical carbocations that may aid in their astrophysical detection.