Frequencies Of Vibrational Bands Research Articles

Raman Spectroscopy Study on Ternary Model Coal Mine Methane Hydrates.

The microfeatures of coal mine methane (CMM) hydrates, synthesized with three gas samples (CH4/C2H6/N2, G1 = 43 : 47 : 10, G2 = 60 : 30 : 10, and G3 = 74 : 16 : 10) in a self-made transparent high-pressure cell at 275.15 K and 5 MPa were investigated using Raman spectroscopy. As a discriminator, the vibrational band frequencies in the C–C regions of the recorded hydrate Raman spectra for C2H6 show that G1∼G3 hydrates are structure I. The three principal parameters used to study the microfeatures of the model CMM hydrates, including cavity occupancies, hydrate guest compositions, and hydration numbers, were calculated. The large cavity occupancies for C2H6 constantly decrease from 85.12 to 79.32%, while the small cavity occupancies for CH4 have a continuous increase from 73.75 to 96.42%. However, CH4 competes with C2H6 on entering the large cavities for their large cavity occupancies of 12.79–17.31%. The cavity occupancies of N2 are less than 1.2%. The hydrate composition calculations show that the molar fractions of C2H6 are the maximum. The hydration numbers range from 6.221 to 6.00. Based on the hydrate guest compositions and hydration numbers, the molecular formulas of the three CMM hydrates are presented.

Vibrational spectra, normal coordinate analysis, and structure of keto form of acetylacetone. A DFT approach

In this paper, we discuss the stability, structure, and vibrational assignment of possible keto forms (Ket1 and Ket2) of acetylacetone, AA, in the gas phase and solutions. The geometry optimization and harmonic and anharmonic vibrational frequencies are calculated at the B3LYP/6-311++G** level. In addition, we also optimize the molecular structure at the MP2/6-311++G(p,d) level. The investigation in solutions is carried out by means of the PCM-SCRF method. We study the relative stability of Ket1 and Ket2 in different media using B2PLYP/6-31+G(d,p) and CBS-QB3 levels. By comparing the IR spectra of AA in a polar solvent, CH3CN, and a nonpolar solvent, CCl4, and considering the theoretical results, the vibrational band frequencies of both keto and enol tautomers are distinguished. Our calculations and vibrational spectra confirm the coexisting of two keto forms in the solutions, designated as Ket1 and Ket2. According to both theoretical and experimental results, Ket1 and Ket2 are predominant in the nonpolar and polar solutions, respectively. In addition, we also do a normal coordinate analysis by using the normal mode eigenvectors obtained at the B3LYP/6-311++ G(d,p) level. The observed vibrational wavenumbers, IR and Raman relative intensities, and Raman depolarization ratios of AA and its deuterated analogous agree satisfactorily with the calculated results obtained at the B3LYP/6-311++G(d,p) method.

Evaluation of degradation in chemical compounds of wood in historical buildings using FT-IR and FT-Raman vibrational spectroscopy

Vibrational spectroscopy approaches like FT-IR and FT-Raman, as analytical method, can be used to assess chemical changes in historical wood structures. In this study, wood samples of three historical buildings, in Gorgan, Iran, namely Tekie Estebar, Molla Esmaiel Mosque, and the Esmaieli Buildings were selected. Wood species was determined by their macroscopic characteristics which were hornbeam (Carpinus betulus), oak (Quercus castaneifolia), beech (Fagus orientalis), and elm (Ulmus glabra), as hardwood species, and yew (Taxus baccata) as a softwood species. Also, some samples of oak were collected from northern and southern sides of the Esmaieli Building in order to compare deterioration environmental factors.. The approximate assignment of the experimental bands was completed by comparing. For this purpose, the experimental bands with the calculated band frequencies of cellulose, hemicellulose and lignin. In addition, the reported assignment for softwood and hardwood was used to confirm the vibrational assignments. The results of spectroscopy revealed that biodegradation had occurred in all species. Comparison between the most important vibrational band frequencies related to carbohydrates and lignin in hardwood species suggested that degradation of carbohydrates was greater than lignin, which could be attributed to brown rot and hydrolysis. Reduction of chemical compounds in south oak samples was higher and could be associated with prevailing wind and UV ray in this side. In the only softwood species (yew), because of its highest exposure to frequent raining, deterioration was observed in both carbohydrates and lignin.

Interaction Enthalpy of Side Chain and Backbone Amides in Polyglutamine Solution Monomers and Fibrils.

We determined an empirical correlation that relates the amide I vibrational band frequencies of the glutamine (Q) side chain to the strength of hydrogen bonding, van der Waals, and Lewis acid-base interactions of its primary amide carbonyl. We used this correlation to determine the Q side chain carbonyl interaction enthalpy (Δ Hint) in monomeric and amyloid-like fibril conformations of D2Q10K2 (Q10). We independently verified these Δ Hint values through molecular dynamics simulations that showed excellent agreement with experiments. We found that side chain-side chain and side chain-peptide backbone interactions in fibrils and monomers are more enthalpically favorable than are Q side chain-water interactions. Q10 fibrils also showed a more favorable Δ Hint for side chain-side chain interactions compared to backbone-backbone interactions. This work experimentally demonstrates that interamide side chain interactions are important in the formation and stabilization of polyQ fibrils.

Computational study of effect of solvents on vibrational spectra of coumarin 500

Abstract Optimized structure of coumarin 500 has been obtained in gas phase and in solvents like methanol, ethanol, dimethyl sulfoxide and CCl4 using density functional theory calculations with B3LYP/6–311 + G(d, p) functionals. The calculated frequencies of certain vibrational bands of coumarin 500 are observed to shift in solvents. To understand the origin of these shifts, HOMO-LUMO analysis of ultra-violet visible spectra of coumarin 500 has been carried out in different solvents. The detailed study of charge transfer interactions in coumarin 500 is done using natural bonding orbital and molecular electrostatic potential analysis. Assignments of various vibrational bands have been obtained and effect of charge transfer interactions in solvents on these bands has been studied.

Low frequency vibrational spectra and the nature of metal-oxygen bond of alkaline earth metal acetylacetonates

Theoretical quantum chemistry calculations were used to assign the observed vibrational band frequencies of Be, Mg, Ca, Sr, and Ba acetylacetonates complexes. Density functional theory (DFT) calculations have been carried out at the B3LYP level, using LanL2DZ, def2SVP, and mixed, GenECP, (def2SVP for metal ions and 6-311++G** for all other atoms) basis sets. The B3LYP level, with mixed basis sets, was utilized for calculations of vibrational frequencies, IR intensity, and Raman activity. Analysis of the vibrational spectra indicates that there are several bands which could almost be assigned mainly to the metal-oxygen vibrations. The strongest Raman band in this region could be used as a measure of the stability of the complex.The effects of central metal on the bond orders and charge distributions in alkaline earth metal acetylacetonates were studied by the Natural Bond Orbital (NBO) method for fully optimized compounds. Optimization were performed at the B3LYP/6-311++G** level for the lighter alkaline earth metal complexes (Be, Mg, and Ca acetylacetonates) while the B3LYP level, using LanL2DZ (extrabasis, d and f on oxygen and metal atoms), def2SVP and mixed (def2SVP on metal ions and 6-311++G** for all other atoms) basis sets for all understudy complexes. Calculations indicate that the covalence nature of metal-oxygen bonds considerably decreases from Be to Ba complexes. The nature of metal-oxygen bond was further studied by using Atoms In Molecules (AIM) analysis. The topological parameters, Wiberg bond orders, natural charges of O and metal ions, and also some vibrational band frequencies were correlated with the stability constants of understudy complexes.

Controlled spectral translucence of nanoporous SiO2/Al2O3 xerogel filled with ammonia and acetone

The near infrared transmission spectra of nanoporous SiO2/Al2O3 xerogel have been recorded for the first time in the process of filling of nanopores with ammonia and acetone molecules. It has been found that the physical adsorption of these gases results in a reversible increase in the translucence of xerogel samples at the frequencies of vibrational bands of surface OH groups.

Isotope shifts in spectra of molecular liquids

In the IR absorption spectra of low-temperature molecular liquids, we have observed anomalously large isotope shifts of frequencies of vibrational bands that are strong in the dipole absorption. The same effect has also been observed in their Raman spectra. At the same time, in the spectra of cryosolutions, the isotope shifts of the same bands coincide with a high accuracy (±(0.1–0.5) cm–1) with the shifts that are observed in the spectra of the gas phase. The difference between the spectra of examined low-temperature systems is caused by the occurrence of resonant dipole–dipole interactions between spectrally active identical molecules. The calculation of the band contour in the spectrum of liquid freon that we have performed in this work taking into account the resonant interaction between states of simultaneous transitions in isotopically substituted molecules can explain this effect.

Hydration of CBr3COOH molecules and CBr3CO 2 – anions in aqueous solutions

The optimal structures and the vibrational frequencies of H-bonded complexes formed from one-two CBr3COOH molecules or the CBr3CO2– anion with water molecules are calculated by density functional theory (B3LYP/6-31++G(d,p)). The comparison of the obtained results with the known Raman spectra of the CBr3COOH–H2O and NaCBr3CO2–·H2O solutions (with component molar ratios of ≤1:16) shows that they include stable hydrates: CBr3COOH·H2O and CBr3CO2–·(H2O)6. The first one has a cyclic form, and the second has a cubic globular form. The vibrational band frequencies of the CBr3COOH molecule and the CBr3CO2– anion in the spectra of both solutions are almost completely determined by the mutual arrangement of units in these hydrates.

Solvation of coumarin6 studied by vibrational spectroscopy and density functional theory

Effect of solvation on coumarin6 dye has been studied with density functional theory (DFT). Optimized structure of the dye has been obtained in various solvents and frequencies of various vibrational bands have been calculated in these solvents. Calculations predict shift in the frequency of certain bands in the solvents. Similar shifts have been observed experimentally in the vibrational spectra of the dye in solvents. In order to ascertain the origin of these shifts, the interactions of solvent molecules with the coumarin6 molecule have been studied using various tools of DFT like donor-acceptor interactions, Molecular Electrostatic potential (MEP) and HOMO-LUMO analysis etc.

Highly sensitive Fourier transform spectroscopy with LED sources

It is shown that the use of high luminance LED emitters as a light source for Fourier transform spectrometers permits to enhance their threshold sensitivity in the visible range by orders of magnitude. Using a 2.5W Edixeon EDEI-1LS3 emitter in the range of 11,350−11,700cm−1 as a light source for the spectrometer with a 60-cm multipass cell during a 24-h measurement time, we have achieved a signal-to-noise ratio of 4.5×104 which corresponds to the minimal detectable absorption coefficient of 1.2×10−8cm−1.Such enhanced sensitivity spectrometer has been used to measure the transition frequencies of CO2 vibrational bands 00051−00001 and 01151−01101 in the range of 11,400−11,500cm−1.

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.

Structure and vibrational assignment of bis(4-amino-3-penten-2-onato)nickel(II). A density functional theoretical study

Bis(4-amino-3-penten-2-onato) nickel(II), (Ni(APO) 2), and its NH deuterated analog, Ni(DAPO) 2, were synthesized and their molecular structure and vibrational assignments were investigated by means of density functional theory (DFT) calculations. The molecular stability was investigated by applying the NBO and geometry calculations. The harmonic vibrational frequencies of Ni(APO) 2 and Ni(DAPO) 2 were obtained at the B3LYP level using 6-311G ∗ basis set. The calculated geometrical parameters and vibrational frequencies were compared with the experimental results. The measured vibrational band frequencies were interpreted in terms of the calculated vibrational normal modes. The scaled theoretical frequencies and the structural parameters were found to be in good agreement with the experimental data.

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.

Calculated dependence of vibrational band frequencies of single-walled and double-walled carbon nanotubes on diameter

We have used density functional theory (DFT) at the B3LYP/6-31G level to calculate Raman and IR spectra of zigzag ( n,0) single-walled carbon nanotubes (SWNTs) and ( n,0) and (2 n,0) double-walled carbon nanotubes (DWNTs), for n ranging from 6 to 19 and 6 to 8, respectively. In the low frequency RBM region, calculated Raman spectra of SWNTs indicate that there are three vibrational modes, with symmetries A 1g, E 1g and E 2g, whose frequencies depend strongly on nanotube diameter. The E 2g mode is not only diameter dependent, but also depends on whether the number of hexagons formed in the circumference direction of the CNT is even or odd. Two IR spectral modes (of A 2u and E 1u symmetries) are found in calculated IR spectra that show strong diameter dependence. Also, three Raman bands with E 1g, A 1g and E 2g symmetries found are to exist in the G-band region. For this latter case, computed spectra indicate that while Raman bands with A 1g symmetry essentially remain constant for even number of hexagons formed in the circumference direction, (e.g., (0,2 n)-type CNTs with band position 1526 ± 0.5 cm −1), bands corresponding to odd number of hexagons, i.e., (0,2 n + 1)-type CNTs, are diameter dependent. The frequencies of the E 1g and E 2g modes (in the G-band region) are not only strongly diameter dependent, but also converge towards one another with increasing tube diameter. This latter type of behavior can lead to erroneous classification of nanotubes as metallic or semiconducting, since partially overlapping bands in the G-band region might result in bands that appear to have diffuse shoulders, a characteristic of metallic SWNTs. The RBMs for DWNTs are also strongly diameter dependent and are blue-shifted relative to their corresponding RBMs in the spectra of SWNTs. The relative distance between RBMs vibrational modes in the spectrum of a selected DWNT is larger than that for the corresponding SWNTs. The electron density for small-sized DWNT, e.g., (6,0)&(12,0), indicates an intratube (inner-outer tube) σ-bonding in the excited state.

Monitoring the Succinate Dehydrogenase Activity Isolated from Mitochondria by Surface Enhanced Raman Scattering

Monitoring enzyme kinetics is an important aspect of biochemistry and is essential when studying metabolism. In this study we demonstrate that succinate dehydrogenase activity of mitochondria can be analyzed quantitatively by surface enhanced Raman scattering (SERS). We used the artificial electron acceptor reporter molecule 2,6-dichlorophenolindophenol (DCPIP) that when oxidized is SERS active. On reduction this redox dye changes from blue to colorless and is SERS inactive. This color change allows UV/vis spectrophotometry to be used as a standard reference measurement as well as SERS. SERS analysis incorporated kinetic time course measurements and employed a portable laser Raman spectrometer using an excitation wavelength of 785 nm in conjunction with gold colloids. Good correlation coefficients and quantitative data were observed with the additional advantage that analysis by SERS also provided good fingerprint spectral information from vibrational band frequencies thus allowing the potential of multiplexing enzyme reactions. We believe that this is the first demonstration of monitoring succinate dehydrogenase activity with SERS and that SERS has considerable potential for being applied to the analysis of metabolic processes.

Structural Analysis of Nanofilms Using FTIR Spectroscopy. An Introduction to the Spectroscopic Analysis of Nanostructures for Undergraduate Students

This exercise introduces students to nanotechnology through the fabrication and analysis of a unique type of nanostructure called a nanofilm. Students prepare self-assembled monolayers (i.e., SAMs) of a series of alkylsiloxanes of differing chain lengths onto glass slides and compare the overall structural quality of these nanofilms as a function of alkyl chain length using FTIR. By monitoring the peak frequencies of certain vibrational bands and through the calculation of vibrational-band ratios, students determine that the overall structural order of alkylsiloxane SAMs decreases as the alkyl chain length of the adsorbed molecule becomes shorter. The use of FTIR for structural analysis is a new concept for undergraduate students who are used to only the qualitative and quantitative capabilities of this analytical technique. In this experiment, students also monitor the durability and wettability of one of the SAM structures.

Reflectance FTIR spectroscopic analysis of metal complexation to EDTA and EDDS

Ethylenediaminetetraacetic acid (EDTA) is a common chelating ligand that is widely used in industry. EDTA, however, is not degradable in present wastewater treatment processes. ( S, S)-Ethylenediaminedisuccinic acid (EDDS), an isomer of EDTA, is biodegradable and has recently received attention as an alternative metal chelating agent for this reason. Investigations reported here utilized reflectance FTIR spectroscopy for the analysis of metal complexation of EDTA and EDDS. The sampling techniques used were diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Similar studies using transmission mode FTIR have been carried out, but the analysis by reflectance techniques described here improved band resolution, minimized matrix interferences, and expanded on the previous work by providing an in situ method for analysis of pH dependence and metal complexation. Structural characteristics of sodium EDTA and EDDS compounds were identified using the results presented here. Complexes of Pb(II), Zn(II), Ni(II), and Cu(II) with EDTA and EDDS were identified by the frequencies of carboxyl group vibrational bands, the difference between asymmetric and symmetric carboxyl groups bands, the relative band intensities, and the band shifts as a result of changes in pH.

Infrared Spectra and ab Initio Calculations for the Cl-−(CH4)n (n = 1−10) Anion Clusters

In an effort to elucidate their structures, mass-selected Cl--(CH4)n (n = 1-10) clusters are probed using infrared spectroscopy in the CH stretch region (2800-3100 cm(-1)). Accompanying ab initio calculations at the MP2/6-311++G(2df,2p) level for the n = 1-3 clusters suggest that methane molecules prefer to attach to the chloride anion by single linear H-bonds and sit adjacent to one another. These conclusions are supported by the agreement between experimental and calculated vibrational band frequencies and intensities. Infrared spectra in the CH stretch region for Cl--(CH4)n clusters containing up to ten CH4 ligands are remarkably simple, each being dominated by a single narrow peak associated with stretching motion of hydrogen-bonded CH groups. The observations are consistent with cluster structures in which at least ten equivalent methane molecules can be accommodated in the first solvation shell about a chloride anion.

Direct Observation of the 4-Methoxyphenylnitrene Intersystem Crossing from S1 to T1 Using Picosecond Kerr-Gated Time-Resolved Resonance Raman Spectroscopy

A picosecond Kerr-gated time-resolved resonance Raman (ps-KTR(3)) study of the singlet 4-methoxyphenylnitrene intersystem crossing to produce the triplet 4-methoxyphenylnitrene species is reported. The experimental resonance Raman vibrational band frequencies observed for the singlet and triplet 4-methoxylphenylnitrene species in the time-resolved Raman experiments are compared to each other and to predictions from previously published density functional theory calculations. The structure, properties, and chemical reactivity of the singlet and triplet states of the 4-methoxyphenylnitrenes are briefly discussed.