Frequencies Of Stretching Modes Research Articles

Sol-gel synthesis and photoluminescent properties of metal oxide-metal oxide coupled nanocomposites

Tin oxide (SnO2) and zinc oxide (ZnO) coupled metal-oxide nanocomposites or SnO2–ZnO were prepared using a sol-gel method. The stretching mode frequencies and crystal structures were examined by using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), respectively. The microscopic analyses by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed a flower-like morphology of the nanocomposites. The analysis of surface chemical and electronic states was conducted by X-ray photoelectron spectroscopy (XPS). The band gap energies as confirmed from the ultraviolet–visible spectroscopy (UV–Vis) data were found to be larger than those of the bulk band gaps due to the increase between energy levels associated with smaller particle sizes. The UV (380 nm) and orange (595) photoluminescence (PL) emissions observed from the SnO2:ZnO nanocomposites were attributed to a combinatorial contribution from radiative transitions in SnO2 and ZnO components. The proposed mechanisms of these emissions are discussed.

Tuning Ice Nucleation by Mussel-Adhesive Inspired Polyelectrolytes: The Role of Hydrogen Bonding

Tuning Ice Nucleation by Mussel-Adhesive Inspired Polyelectrolytes: The Role of Hydrogen Bonding

Speciation and solubility of rhenium in borosilicate waste glasses

Rhenium is frequently used as a non-radioactive surrogate for technetium. Speciation and solubility of rhenium in borosilicate nuclear waste glasses are investigated, where Raman spectroscopy shows rhenium in perrhenate (ReO4−) environments. Perrhenate solubility varied considerably at 1150 °C in ambient air in five different composition glasses, from 10,000 ppm Re for lithium alumino-borosilicate glass to near 4000 ppm for complex U.S. LAW and Japanese HLW glasses. Network modifying cation composition, especially lithium, strongly affect perrhenate solubility. Re-O symmetrical stretch mode (ν1Re-O) frequencies shift depending on the alkali cation mix in the glasses, while ν1Re-O widths are similar for all glasses studied, indicating random mixing of network modifying cations, especially Li+and Na+, around ReO4−. Perrhenate ν1Re-O areas track with Re concentrations, indicating that most, if not all, Re in the glass is in perrhenate environments. Mo added to these glasses did not significantly affect Re solubility, nor ν1Re-O behavior.

Compressibility and blue-shifting O–H stretching bands of magnesium hydroxyfluoride Mg(OH)F up to 20 ​GPa

In-situ high-pressure synchrotron X-ray diffraction (XRD) and Fourier transform infrared absorption spectroscopy (FTIR) measurements have been conducted up to ~20 ​GPa at room temperature using diamond anvil cells (DAC), to investigate compressibility and spectroscopic properties of magnesium hydroxyfluoride, Mg(OH)F (Pnma, Z ​= ​4). Without any phase transition being observed, the pressure-volume correlation is fitted by the second-order Birch-Murnaghan equation of state, yielding K0 ​= ​80 (±2) GPa, K0′ ​= ​4.0 (fixed), and V0 ​= ​145.2 (±0.3) Å3. In accordance with other isostructural compounds crystallizing in the diaspore-type structure, higher contraction occurs along the c axis of Mg(OH)F. Positive pressure dependence of the O–H stretching mode frequencies initially observed at 3537 (1.56 ​cm−1/GPa), 3641 (0.67 ​cm−1/GPa), and 3680 ​cm−1 (2.85 ​cm−1/GPa) at ambient pressure indicates that the O–H⋯F hydrogen bond does not strengthen under compression.

Microstructural, FTIR and Raman spectroscopic study of Rare earth doped ZnO nanostructures

Yb doped ZnO nanorods were prepared on glass substrates by the hydrothermal method in order to investigate the insertion of Yb ions in the ZnO matrix and the related morphological, structural and vibrational properties of the samples. X-ray diffraction patterns showed that the undoped and Yb doped ZnO nanorods exhibit the hexagonal wurtzite crystal structure with a preferential orientation along (1 0 1) direction and the size of the particle is found to be decreased with Yb content. SEM images show rods shape with more agglomeration in Yb doped ZnO nanorods. The vibrational study has also been performed using FT-IR spectroscopy which gives the presence of an absorption band corresponding to the stretching mode frequency of ZnO (Zn−O), the bands corresponding to organic precursors were no longer present in the FTIR spectrum after doping, which supports the incorporation of Yb ions into the ZnO lattice. Raman spectra confirmed the hexagonal wurtzite structure of pure and Yb doped ZnO nanoparticles with E2 (high) mode at 438 cm−1 and the presence of other possible defects. The aim of this study was to investigate the effect of Yb doping on the structural and vibrational properties of ZnO nanorods.

Effect of the weak intermolecular C-H···O=C hydrogen bonding, solvent polarity and concentration on the frequency of the C=O stretch mode of 2-thiophenecarboxaldehyde

The vibrational frequency shift in the C=O stretch mode of 2-thiophenecarboxaldehyde (2TC) in the condensed phase is still not fully understood. In this paper, the vibrational spectra of 2TC were investigated using the FT-Raman, FT-IR and resonance Raman spectroscopies in conjunction with the density functional theory calculation. The pure compound (in the neat liquid) exhibits three vibrational bands 1658, 1672 and 1687 cm−1 in the νC=O spectral region. It differs from the band pair 1672 and 1682 cm−1 for 2-cyclohexene-1-one (CHO) and the single band 1700 cm−1 for benzaldehyde. The relative intensities of observed bands vary with the polarity of aprotic solvents and the compound’s concentration. In a diluted solution, the strongest band in the resonance Raman spectra of 2TC appears the C=O stretch mode at 1690 cm−1 in cyclohexane and 1674/1675 cm−1 in acetonitrile. The imparting factors that shift the C=O stretch mode frequency in the neat liquid and solvents with different polarities were examined. The spectral sources of the vibrational bands at 1658 and 1672 cm−1 in the neat liquid and a dilute solution were determined, and the resonance Raman spectra were assigned. It is concluded that tetramers and monomer are the major sources of the bands at 1658 and 1672 cm−1 in the neat liquid, respectively, while the monomer is the main source of the bands at 1674/1675 cm−1 in acetonitrile and the band at 1690 cm−1 in cyclohexane with a dilute concentration. The band’s source at 1662/1663 cm−1 in acetonitrile (a dilute concentration) can be either the dimers or 2TC-CH3CN clusters. The C=O bond’s electronic charge density is the main factor that shifts the vibrational frequency of the C=O stretch mode of 2TC monomer when an aprotic solvent is used. The larger the polarity of an aprotic solvent, the more negative the electronic charge-density of the C=O bond for the monomer, the lower the frequency of the C=O stretch mode.

Free Vibration Analysis of Thick Isotropic Plate by Using 5th Order Shear Deformation Theory

In the present study, a 5th order shear deformation theory (5th OSDT) is presented for free vibration analysis of simply supported thick isotropic plates. Governing equations and boundary conditions are evaluated using the concept of virtual work. Numerical results for free vibration analysis include the effects of side to thickness and plate aspect ratios for simply supported thick isotropic plates. Non-dimensional bending mode frequencies, non-dimensional thickness shear mode frequencies and non-dimensional thickness stretch mode frequencies are obtained. Closed form analytical solutions for simply supported isotropic thick plates subjected to single sinusoidal distributed loads are obtained for comparison purpose. The problems considered in this study are solved using MATLAB software. Non-dimensional bending frequencies and non-dimensional thickness shear mode frequencies obtained through the 5th OSDT match well with the exact analytical and exponential shear deformation theory (ESDT) results. Further, the non-dimensional thickness stretch mode frequencies are found to be imaginary.

Pressure-Induced Amorphization of Diisopropylammonium Perchlorate Studied by Raman Spectroscopy and X-ray Diffraction.

Diisopropylammonium salts have drawn attention in recent years due to their room-temperature ferroelectric properties. Triclinic diisopropylammonium perchlorate (DIPAP) exhibits ferroelectricity at room temperature. We have carried out density functional theory calculations to assign the phonon modes in DIPAP. High-pressure Raman spectra of DIPAP are recorded up to ∼3 GPa. Discontinuity in the NH2 bending and stretching mode frequencies and the appearance of new bands at 0.7 GPa suggest a phase transition by a rearrangement in the hydrogen network. Broadening of lattice modes at 1.3-1.7 GPa indicates a loss of crystalline nature above 1.7 GPa. High-pressure synchrotron X-ray diffraction of DIPAP shows an isostructural phase transition at 0.6 GPa and confirms amorphization at 1.5 GPa that may lead to a loss of ferroelectricity above this pressure. The ambient phase becomes reversible after releasing the pressure. The bulk modulus of DIPAP is determined to be 16.5 GPa.

Vibrational response and motion of carbon monoxide on Cu(100) driven by femtosecond laser pulses: Molecular dynamics with electronic friction

Carbon monoxide on copper surfaces continues to be a fascinating, rich microlab for many questions evolving in surface science. Recently, hot-electron mediated, femtosecond-laser pulse induced dynamics of CO molecules on Cu(100) were the focus of experiments [Inoue et al., Phys. Rev. Lett. 117, 186101 (2016)] and theory [Novko et al., Phys. Rev. Lett. 122, 016806 (2019)], unraveling details of the vibrational nonequilibrium dynamics on ultrashort (subpicoseconds) timescales. In the present work, full-dimensional time-resolved hot-electron driven dynamics are studied by molecular dynamics with electronic friction (MDEF). Dissipation is included by a friction term in a Langevin equation which describes the coupling of molecular degrees of freedom to electron-hole pairs in the copper surface, calculated from gradient-corrected density functional theory (DFT) via a local density friction approximation (LDFA). Relaxation due to surface phonons is included by a generalized Langevin oscillator model. The hot-electron induced excitation is described via a time-dependent electronic temperature, the latter derived from an improved two-temperature model. Our parameter-free simulations on a precomputed potential energy surface allow for excellent statistics, and the observed trends are confirmed by on-the-fly ab initio molecular dynamics with electronic friction (AIMDEF) calculations. By computing time-resolved frequency maps for selected molecular vibrations, instantaneous frequencies, probability distributions, and correlation functions, we gain microscopic insight into hot-electron driven dynamics and we can relate the time evolution of vibrational internal CO stretch-mode frequencies to measured data, notably an observed redshift. Quantitatively, the latter is found to be larger in MDEF than in experiment and possible reasons are discussed for this observation. In our model, in addition we observe the excitation and time evolution of large-amplitude low-frequency modes, lateral CO surface diffusion, and molecular desorption. Effects of surface atom motion and of the laser fluence are also discussed.

Narrowband ultraviolet B emitting Gd3+ activated NaSrPO4 phosphor prepared by co-precipitation method

Sodium strontium phosphate or NaSrPO4 phosphor activated with gadolinium (Gd3+) was prepared by co-precipitation method. The X-ray diffraction (XRD) pattern confirmed that the phosphor crystallized in a monoclinic phase of NaSrPO4. The Fourier transform infrared spectroscopy (FTIR) data confirmed that the stretching mode frequencies were related to stretching vibrations of (PO4)3− group. The photoluminescence emission spectrum showed characteristic emissions of Gd3+ at 313 nm (6P7/2→8S7/2). The EPR spectrum of gadolinium activated NaSrPO4 phosphor exhibited resonance signals at effective values of g ≈ 5.95, 4.90 and 2.02 indicating the existence gadolinium in trivalent state in the NaSrPO4 phosphor matrix.

Structure and optical properties of La2-xGdxSiO5:Dy3+ phosphors

Lanthanum gadolinium oxyorthosilicate or La2-xGdxSiO5 (x = 0, 0.5, 1.0, 1.5 and 2.0) nanophosphors doped with dysprosium (Dy3+) were prepared by urea- and ammonium nitrate-assisted solution combustion method. The X-ray diffraction (XRD) patterns confirmed that the phosphors crystallized in a mixed phase of La2SiO5 and La(OH)3 and a pure monoclinic phase of Gd2SiO5 or the admixtures of the three phases depending on the ratio of La:Gd in the host lattice. The estimated crystallite sizes were found to vary from 10 to 21 nm. The field emission scanning electron microscopy (FE-SEM) images showed that the particles were agglomerated together and they had no definite sizes. The chemical composition analyses and the electronic states were analyzed using the energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) respectively. The Fourier transform infrared spectroscopy (FTIR) data supplemented both the XRD and EDS data by confirming that the stretching mode frequencies were all related to La2SiO5 and Gd2SiO5, except a few absorption peaks ascribed to atmospheric moisture and hydrocarbons. The band gaps measured from the ultraviolet visible spectroscopy (UV–Vis) data were shown to vary with the molar ratio of La to Gd. The photoluminescence spectra showed two characteristic emissions of Dy3+ at 485 nm (blue) and 573 nm (yellow) and an additional broad emission (in the blue region) with a maximum at ∼415 nm. The International Commission on Illumination (CIE) chromaticity coordinates calculated from the fluorescence emission showed colours which were tuned from blue to white and yellow when the molar ratio of La to Gd in the La2-xGdxSiO5:Dy3+ lattice was varied. Depending on the excitation wavelength, energy transfer was observed from Dy3+ substituted in Gd3+ lattice sites to Dy3+ substituted in La3+ lattice sites. The internal photoluminescence quantum yield of the phosphors was measured using an integrating sphere method.

Strong Hydrogen Bonds at the Interface between Proton-Donating and -Accepting Self-Assembled Monolayers on Au(111)

Hydrogen-bonding heterogeneous bilayers on substrates have been studied as a base for new functions of molecular adlayers by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), and density functional theory (DFT) calculations. Here, we report the formation of the catechol-fused bis(methylthio)tetrathiafulvalene (H2Cat-BMT-TTF) adlayer hydrogen bonding with an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) on Au(111). The heterogeneous bilayer is realized by sequential two-step immersions in solutions for the individual Im-SAM and H2Cat-BMT-TTF adlayer formations. In the measurements by AFM, a grained H2Cat-BMT-TTF adlayer on Im-SAM is revealed. The coverage and the chemical states of H2Cat-BMT-TTF on Im-SAM are specified by XPS. On the vibrational spectrum measured by IRAS, the strong hydrogen bonds between H2Cat-BMT-TTF and Im-SAM are characterized by the remarkably red-shifted OH stretching mode at 3140 cm-1, which is much lower than that for hydrogen-bonding water (typically ∼3300 cm-1). The OH stretching mode frequency and the adsorption strength for the H2Cat-BMT-TTF molecule hydrogen bonding with imidazole groups are quantitatively examined on the basis of DFT calculations.

Low Melting Tetracyanidoborate Salts with Alkyl‐, Arylammonium, and Pyridinium Cations: Syntheses, Structures, Properties.

AbstractThe syntheses and single crystal structures of five new tetracyanidoborate salts with N‐based cations are described. Three of these compounds contain cations with acidic H atoms. The H‐bond strength, expressed by D‐A distances is correlated with a shift of the CN stretching mode frequency in the IR spectra. Melting points are found between 59 °C and 214 °C, i. e. at the borderline between ionic liquids and molten salts. Isothermal annealing indicates slow decomposition. Solubility tests in polar solvents show a strong dependence on the cation.

X-ray absorption and Raman spectroscopy studies of molybdenum environments in borosilicate waste glasses

Mo-containing high-level nuclear waste borosilicate glasses were investigated as part of an effort to improve Mo loading while avoiding yellow phase crystallization. Previous work showed that additions of vanadium decrease yellow phase formation and increases Mo solubility. X-ray absorption spectroscopy (XAS) and Raman spectroscopy were used to characterize Mo environments in HLW borosilicate glasses and to investigate possible structural relationships between Mo and V. Mo XAS spectra for the glasses indicate isolated tetrahedral Mo6+O4 with Mo-O distances near 1.75 Å. V XANES indicate tetrahedral V5+O4 as the dominant species. Raman spectra show composition dependent trends, where Mo-O symmetrical stretch mode frequencies (ν1) are sensitive to the mix of alkali and alkaline earth cations, decreasing by up to 10 cm−1 for glasses that change from Li+ to Na+ as the dominant network-modifying species. This indicates that MoO4 tetrahedra are isolated from the borosilicate network and are surrounded, at least partly, by Na+ and Li+. Secondary ν1 frequency effects, with changes up to 7 cm−1, were also observed with increasing V2O5 and MoO3 content. These secondary trends may indicate MoO4-MoO4 and MoO4-VO4 clustering, suggesting that V additions may stabilize Mo in the matrix with respect to yellow phase formation.

Structure and Dynamics of the Lithium Ion Solvation Shell in Linear Organic Carbonates By Two-Dimensional Infrared Spectroscopy

The development of better energy storage technologies is required for a sustainable growth of the world population. Numerous different technologies have been developed and applied for energy storage in the last decades. Currently, the most utilized technology relies on electrochemical reduction and oxidation of lithium. Although the lithium technology has been developed for more than 10 years, the structure of the lithium ion solvation shell is still under debate. It has been previously suggested that the coordination number of organic carbonate molecules around the lithium ion can be 4 and 6, but no definitive conclusions have been derived from these experiments. Previous infrared studies on lithium ion battery electrolytes have been limited by the high optical density of the carbonate solvents, resulting in researchers studying dilute systems instead of the true lithium ion battery electrolyte. Using a novel spectroscopic sample cell, we have used linear infrared (FTIR) and two-dimensional infrared (2DIR) spectroscopies in combination with density functional theory (DFT) calculations to study lithium hexafluorophosphate salt (LiPF6) dissolved in pure carbonate solvents (dimethyl carbonate and diethyl carbonate) at concentrations of ca. 1.5 M. In agreement with previous studies our infrared experiments show the presence of two infrared bands in the carbonyl stretching region: low and high frequency bands. These two bands have been traditionally assigned to the lithium-coordinated carbonyl stretch (low frequency band) and to the free carbonyl stretch (high frequency band). However, in the 2DIR spectra of LiPF6in either linear carbonate solvent, the spectrum shows the presence of a cross peak between the “free” and “coordinated” carbonyl stretches at a waiting time of 0 fs indicating coupling between the two vibrational states. Thus, a new assignment of the peak is proposed in which the lithium ion has a tetrahedral arrangement of linear carbonate molecules. In this molecular arrangement, the low frequency band is due to the overlap of three asymmetric carbonyl stretches arising from the tetrahedral structure of the carbonates around the Li ion, while the high frequency band is due to both the uncoordinated carbonate molecules as well as the symmetric carbonyl stretching mode arising from the tetrahedral complex, which for a perfect tetrahedral is not IR active. This assignment is perfectly consistent with the experimental observations of both this work and previous studies. Notably, the use of 2DIR spectroscopy also demonstrates that the lithium ion solvation shell is not a perfect tetrahedron as seen by the presence of a cross peak at 0 fs waiting time. This cross peak arises from the imperfect geometry of the tetrahedral solvation shell of the complex that makes the symmetric stretch infrared active since it is not expected that the carbonates of the lithium solvation shell, which have the carbonyl groups pointing towards the cation, have a strong coupling with the surrounding “free” carbonates. Thus, in the context of a symmetrically broken tetrahedral structure, the “dark” symmetric stretching mode will be overlapped with the “free” carbonyl stretching mode. Ab-initio calculations confirm the existence of the observed infrared bands, and they assign them to three frequency overlapped asymmetric carbonyl stretching modes and the weaker symmetric carbonyl stretching mode frequency, which overlaps with the “free” carbonyl stretch. Moreover, these theoretical calculations present an excellent agreement for the ratio of transition dipoles, strongly supporting the new assignment of the bands and the solvation structure consisting of four coordinated carbonates in a tetrahedron arrangement. Our studies also provide dynamical information of the system. In these electrolytes, the asymmetric stretching band of the diethyl carbonate solution shows significantly longer frequency frequency correlation time than that of the dimethyl carbonate solution which indicates that the diethyl carbonates coordinated to the Li ion have slower structural motions than the Li ion coordinated dimethyl carbonate molecules. In addition, our results show that the difference observed in the dynamics are not likely to arise from the motions of the solvent molecules since the solvent motions for both carbonates have very similar time scales. Thus, the difference in the dynamics is belived to be associated with either the energetics of the Li-carbonyl interactions or the presence of solvent separated ion-pairs.

Structure and photoluminescent properties of green-emitting terbium-doped GdV1-x Px O4 phosphor prepared by solution combustion method.

Terbium-doped gadolinium orthovanadate (GdVO4 :Tb(3+) ), orthophosphate monohydrate (GdPO4 ·H2 O:Tb(3+) ) and orthovanadate-phosphate (GdV,PO4 :Tb(3+) ) powder phosphors were synthesized using a solution combustion method. X-Ray diffraction analysis confirmed the formation of crystalline GdVO4 , GdPO4 ·H2 O and GdV,PO4 . Scanning electron microscopy images showed that the powder was composed of an agglomeration of particles of different shapes, ranging from spherical to oval to wire-like structures. The chemical elements present were confirmed by energy dispersive spectroscopy, and the stretching mode frequencies were determined by Fourier transform infrared spectroscopy. UV-visible spectroscopy spectra showed a strong absorption band with a maximum at 200 nm assigned to the absorption of VO4 (3-) and minor excitation bands assigned to f → f transitions of Tb(3+) . Four characteristic emission peaks were observed at 491, 546, 588 and 623 nm, and are attributed to (5) D4 → (7) Fj (j = 6, 5, 4 and 3). The photoluminescent prominent green emission peak ((5) D4 → (7) F5 ) was centred at 546 nm. The structure and possible mechanism of light emission from GdV1-x Px O4 :% Tb(3+) are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Temperature Dependence of Light-Induced Absorbance Changes Associated with Chlorophyll Photooxidation in Manganese-Depleted Core Complexes of Photosystem II.

Mid-infrared (4500-1150 cm(-1)) absorbance changes induced by continuous illumination of Mn-depleted core complexes of photosystem II (PSII) from spinach in the presence of exogenous electron acceptors (potassium ferricyanide and silicomolybdate) were studied by FTIR difference spectroscopy in the temperature range 100-265 K. The FTIR difference spectrum for photooxidation of the chlorophyll dimer P680 was determined from the set of signals associated with oxidation of secondary electron donors (β-carotene, chlorophyll) and reduction of the primary quinone QA. On the basis of analysis of the temperature dependence of the P680(+)/P680 FTIR spectrum, it was concluded that frequencies of 13(1)-keto-C=O stretching modes of neutral chlorophyll molecules PD1 and PD2, which constitute P680, are similar to each other, being located at ~1700 cm(-1). This together with considerable difference between the stretching mode frequencies of keto groups of PD1(+) and PD2(+) cations (1724 and 1709 cm(-1), respectively) is in agreement with a literature model (Okubo et al. (2007) Biochemistry, 46, 4390-4397) suggesting that the positive charge in the P680(+) dimer is mainly localized on one of the two chlorophyll molecules. A partial delocalization of the charge between the PD1 and PD2 molecules in P680(+) is supported by the presence of a characteristic electronic intervalence band at ~3000 cm(-1). It is shown that a bleaching band at 1680 cm(-1) in the P680(+)/P680 FTIR spectrum does not belong to P680. A possible origin of this band is discussed, taking into account the temperature dependence (100-265 K) of light-induced absorbance changes of PSII core complexes in the visible spectral region from 620 to 720 nm.

The vacancy–hydrogen defect in diamond: A computational study

AbstractHydrogen is grown into CVD diamond and occurs in point defects also involving a lattice vacancy, V. Complexes involving V, H and nitrogen, or silicon have been identified by experiment, and in some cases the microscopic structure has been identified with the use of quantum‐chemical simulations. In this study, we present the results of density functional simulations of the primitive vacancy‐hydrogen defect in diamond. We find that the symmetry of the VH defect is , with the H atom strongly bonded to one of the four C radicals that are formed when the vacancy is created. The defect is expected to occur in both the neutral and negatively charged forms, with the possibility of both positive and charge states.For VH0, and spin states are found to be indistinguishable in energy, with the quartet not expected to yield sharp optical transitions, unlike the doublet. VH in the ground‐state is predicted to have an optical transition that is broadly similar to that of N (), although it is important to note that the non‐degenerate band involved in the transitions arises from a different origin in VH as there are no lone‐pairs present in this case. We have also made predictions for the C–H stretch mode frequencies, noting a general trend with charge state. Combinations of optical spectroscopy, paramagnetic resonance and vibrational mode spectroscopy are therefore required to fully experimentally resolve VH in its various charge and spin states.

Ion aggregation in high salt solutions. III. Computational vibrational spectroscopy of HDO in aqueous salt solutions.

The vibrational frequency, frequency fluctuation dynamics, and transition dipole moment of the O-D stretch mode of HDO molecule in aqueous solutions are strongly dependent on its local electrostatic environment and hydrogen-bond network structure. Therefore, the time-resolved vibrational spectroscopy the O-D stretch mode has been particularly used to investigate specific ion effects on water structure. Despite prolonged efforts to understand the interplay of O-D vibrational dynamics with local water hydrogen-bond network and ion aggregate structures in high salt solutions, still there exists a gap between theory and experiment due to a lack of quantitative model for accurately describing O-D stretch frequency in high salt solutions. To fill this gap, we have performed numerical simulations of Raman scattering and IR absorption spectra of the O-D stretch mode of HDO in highly concentrated NaCl and KSCN solutions and compared them with experimental results. Carrying out extensive quantum chemistry calculations on not only water clusters but also ion-water clusters, we first developed a distributed vibrational solvatochromic charge model for the O-D stretch mode in aqueous salt solutions. Furthermore, the non-Condon effect on the vibrational transition dipole moment of the O-D stretch mode was fully taken into consideration with the charge response kernel that is non-local polarizability density. From the fluctuating O-D stretch mode frequencies and transition dipole vectors obtained from the molecular dynamics simulations, the O-D stretch Raman scattering and IR absorption spectra of HDO in salt solutions could be calculated. The polarization effect on the transition dipole vector of the O-D stretch mode is shown to be important and the asymmetric line shapes of the O-D stretch Raman scattering and IR absorption spectra of HDO especially in highly concentrated NaCl and KSCN solutions are in quantitative agreement with experimental results. We anticipate that this computational approach will be of critical use in interpreting linear and nonlinear vibrational spectroscopies of HDO molecule that is considered as an excellent local probe for monitoring local electrostatic and hydrogen-bonding environment in not just salt but also other confined and crowded solutions.

Vibrational and electronic spectroscopic studies of melatonin

We report the infrared absorption and Raman spectra of melatonin recorded with 488 and 632.8nm excitations in 3600–2700 and 1700–70cm−1 regions. Further, we optimized molecular structure of the three conformers of melatonin within density functional theory calculations. Vibrational frequencies of all three conformers have also been calculated. Observed vibrational bands have been assigned to different vibrational motions of the molecules on the basis of potential energy distribution calculations and calculated vibrational frequencies. Observed band positions match well with the calculated values after scaling except NH stretching mode frequencies. It is found that the observed and calculated frequencies mismatch of NH stretching is due to intermolecular interactions between melatonin molecules.