Shoulder Band Research Articles

Investigating structural property of human hair by using infrared free electron lasers

Intense infrared (IR) rays can heat matters and evaporate waters thermally. One of the possible applications will be hair dryer, although the irradiation effects of IR rays on the hair have not been fully explored. In this study, we first examined the interaction of IR rays at various wavelengths from 3.0 µm (near IR) to 90 µm (far IR) with the surface structure of human hair by using IR free electron lasers (FELs). IR-FEL is an accelerator-based pico-second pulse laser, and the feature is the wavelength-tunability with the high-photon density. When one thread of hair was irradiated by the FEL of 6–7 mJ energy at 60 µm, the cleavage occurred, and the morphological destruction was observed on scanning-electron microscopy images after the irradiations at 70 µm and 6.1 µm (amide I). Synchrotron-radiation infrared microspectroscopy showed that those FEL irradiations decreased a shoulder band at 1710 cm−1 that corresponds to carboxyl group in melanin or fatty acids and increased absorption intensity at 500–600 cm−1. On the contrary, the FEL at 90 µm little changed either the surface morphology or the infrared absorption spectra. Interestingly, near-IR FELs at 3.0–3.5 µm induced bending of a hair, and 2D mapping of protein secondary conformations revealed that β-sheet was more increased than the other conformations on the surface of the bending area even at low pulse energy (1–3 mJ). As a result, the structural damage of the hair was least at 90 µm, which implies an ideal wavelength for drying hair mildly.

Clarifying the role of carboxyl functionality in squaraines towards aggregation and self-assembly through photophysical characterization and BSA interactions

The demand for near-infrared (NIR) probes with robust and stable fluorescence signals has surged, driven by their applications in optical sensing and bioimaging. Squraine dyes as NIR fluorescent probes have gained significant traction. However, understanding their behavior in aqueous media is important for their successful application. Herein we report the synthesis and photophysical characterization of carboxy-functionalized unsymmetrical squaraine dyes capable of light absorption and emission in the near-infrared (NIR) wavelength region. Structural variations in alkyl chain length, and spacer chain length between the primary chromophore and –COOH group were systematically introduced to investigate their impact on self-assembly in aqueous media leading to dye aggregation and their differential interactions with Bovine Serum Albumin (BSA) as a model protein. In phosphate buffer (PB) the absorption intensity decreased drastically along with pronounced shoulders due to dye aggregation leading to complete fluorescence quenching. However, in the presence of BSA, the intensity of shoulder bands reduced coupled with a sharp increase in the absorption associated with monomeric dye with the increasing concentration of BSA, indicating the prevention of dye aggregation owing to dye-BSA interactions. The prevention of dye aggregation due to dye-BSA interaction also led to a tremendous increase in the fluorescence intensities as a function of the increasing BSA concentrations. Site-selective study off BSA showed that these dyes bind preferably at Site-II using hydrophilic interactions. Thus, these dyes show great potential as FRET or fluorescent on/off probes for biosensing, non-covalent labeling of proteins, and fluorescent probes for bioimaging.

Perimidocarbene-Based Tetradentate Platinum(II) Complexes with an Unexpectedly Negligible 3MLCT Character.

Two novel six-membered perimidocarbene (PIC)-based tetradentate Pt(II) complexes were designed and successfully synthesized. Systematical experimental and theoretical studies suggest that the PIC moiety greatly affects the frontier orbitals, as well as the photophysical and excited-state properties of the Pt(II) complexes. PtYK2 has a broad emission spectrum peaking at 576 nm with a shoulder band at 620 nm, along with a full width at half-maximum (FWHM) value of 100.0 nm at 77 K in 2-MeTHF; however, the emission spectrum is slightly red-shifted with a dominant peak at 610 nm and a FWHM value of 125.0 nm at room temperature in a poly(methyl methacrylate) (PMMA) film. Time-dependent-density functional theory and natural transition orbital analyses reveal that PtYK2 has a 3LC (3πPIC* → πPIC)-dominated character with an unexpectedly negligible contribution of 3MLCT transition (0.68%) in the T1 state, which results in a broad emission spectrum and a relatively low quantum efficiency of 7.4% in the PMMA film.

Analytical method for stable background reduction for Raman spectra of carbon‐containing meteorite and terrestrial samples suffering from intense fluorescence

AbstractChemical states of carbon in terrestrial (meta) sediments and carbonaceous chondrites gather attention as a geothermometer. As a nondestructive analytical method, Raman spectroscopy has been widely used to study their electronic properties, crystallinity, and structural defects through so‐called D and G bands. For the analysis of Raman spectra, a common problem is coexistence of a fluorescence background, which should be subtracted prior to the peak‐fitting analysis. However, we recently faced a problem that the band shape noticeably changed depending on the background function assumed although the background seemed to be well subtracted at a first glance regardless of the choice of the background function. For the application of the Raman spectroscopy as a geothermometer, a standard background subtraction method must be established to suppress the arbitrariness. In the present study, Raman spectra of seven carbon‐containing natural samples, whose background intensities were significantly different, were measured, and their background shape was evaluated by first‐, second‐, and third‐order polynomials. The results indicated that the third‐order polynomial was necessary and sufficient as a standard background function. Importantly, although lower order polynomials seem to successfully fit the background at a first glance, they falsely caused dispersion of the shoulder band shape.

Synthesis and Properties of Nonaromatic meso-fused Heterobenzihomoporphyrin(2.1.1.1)s.

Fluorene-based tripyrrane has been used as a fused precursor to synthesize three novel examples of nonaromatic meso-fused thia and selenabenzihomoporphyrin(2.1.1.1)s by condensing it with appropriate 2,5-bis(hydroxymethyl)aryl thiophene or selenophene under acid catalyzed conditions. The meso-fused heterobenzihomoporphyrins contain one fluorene unit, two pyrrole rings and one thiophene/selenophene ring connected via five meso-carbons in the macrocyclic framework. The macrocycles were thoroughly characterized by HR-MS, 1D and 2D NMR, absorption, cyclic voltammetry and DFT/TD-DFT studies. NMR, absorption, and DFT studies indicated the nonaromatic nature of meso-fused heterobenzihomoporphyrins. The macrocycles displayed one intense band at ∼380 nm along with a shoulder band at 450 nm and a broad band in the region of 590-850 nm which were bathochromically shifted in the monoprotonated derivatives and absorbed prominently in the NIR region with the peak maxima at ∼1035 nm. The electrochemical studies revealed that the macrocycles showed three well-defined oxidations and reductions, and TD-DFT studies corroborated experimental observations.

Synthesis and Studies of Fused Benzo-Benzisapphyrins.

A series of rare examples of fused benzo-benzisapphyrins were synthesized readily by (3 + 2) condensation of benzodipyrrole-derived diol and para-benzitripyrrane in the presence of 0.5 equiv of TFA in CH2Cl2 under inert atmosphere conditions accompanied by DDQ oxidation in open air. The crude compounds were separated by basic alumina column chromatography and afforded pure fused benzo-benzisapphyrins in 20-22% yields. The fused sapphyrins were characterized in detail by high-resolution mass spectrometry (HRMS) and one-dimensional (1D) and two-dimensional (2D) NMR spectroscopy. The 1H NMR spectra recorded at both 298 and at 233 K clearly exhibited the presence of a strong diatropic ring current in benzo-benzisapphyrins, and the macrocycles are of aromatic nature. The DFT-optimized structure of benzo-benzisapphyrin revealed that the macrocycle was planar to a great extent due to the rigid structure of the dibenzopyrrole moiety, and the NICS(0) value of -11.2 ppm supports the aromatic nature of macrocycles. The absorption spectra of benzo-benzisapphyrins showed three weak Q bands approximately in the region of 650-900 nm and a strong Soret band at 480 nm, along with a shoulder band at ∼510 nm. The diprotonated derivative generated by the addition of excess TFA to the benzo-benzisapphyrin macrocycle exhibited bathochromically shifted absorption bands compared to the free base macrocycle.

Fourier transform infrared spectroscopy (FTIR) characteristics of ancient amber artifacts of the Han Dynasty from Hunan, China

Here we analyze four ancient amber artifacts of the Han Dynasty (202 BCE–220 CE) by using Fourier transform infrared spectroscopy to reveal their origins. The FTIR results showed the presence of the Baltic shoulder band between 1210–1150 cm-1 and the weak absorption peak near 888 cm-1, so all amber artifacts analyzed here can be classified as succinite originating from the Baltic Sea area (or also Bitterfield or Ukrainian ambers which are Baltic amber coevals). Ancient amber could have been traded from the Baltic area to the Mediterranean via the amber road, and then to the East Asia along the Silk Road. Such exotic materials represent a key for the study of long-distance trade across cultures during ancient times. Very few ancient amber samples excavated in China have been analyzed scientifically so far, and more work is required.

Structural characterizations on the degradation of 2D organic–inorganic hybrid perovskites and its enlightenment to improved stability

Despite the demonstrated high-efficiency of solar cells and light-emitting devices based on two-dimensional (2D) perovskites, intrinsic stability of the 2D perovskites is yet far from satisfactory. In this work, we find the 2D (BA)2PbI4 perovskite crystals rapidly degrade in the ambient conditions and the photoluminescence (PL) nearly completely quenches in 6 d. Moreover, the PL shoulder band due to defects and absorption band of PbI2 gradually rise during degradation, suggesting the precipitation of PbI2. Besides, rod structures are observed in the degraded crystals, which are attributed to the formation of one-dimensional (1D) (BA)3PbI5 perovskites. And the degradation can be largely retarded by decreasing the humidity during storage. Therefore, a chemical reaction for the degradation of (BA)2PbI4 is proposed, revealing the interactions between water molecules and undercoordinated defects are very critical for understanding the degradation. Enlightened by these findings, dimethyl itaconate (DI) treatment is developed to passivate the defects and block the intrusion of moisture to improve the stability of the (BA)2PbI4. After storage in the ambient environment for 16 d, the DI treated (BA)2PbI4 only shows a slight surface degradation without formation of any nanorod-like structures, and the PL intensity retains about 70%. Therefore, our systematic study provides a comprehensive understanding on the degradation dynamics of 2D perovskites, which will promote future development of intrinsically stable 2D perovskites.

Synthesis of Pyridine-Containing Crowned Fused Expanded Porphyrins.

New examples of nonaromatic fused expanded porphyrins containing both pyridine and crown ether moiety as a part of macrocyclic framework were synthesized by condensing pyridine based pentapyrrane with polyether-based diol in CH2 Cl2 in the presence of one equivalent of BF3 ⋅ OEt2 under inert conditions followed by oxidation with DDQ in open air. The condensation was expected to form pyridine-containing crowned expanded porphyrins but resulted in the formation of fused crowned expanded porphyrins due to intramolecular fusion of two pyrrole nitrogens with two adjacent inverted thiophene carbons as revealed by X-ray crystallography obtained for one of the macrocycle. HRMS and NMR studies supported the formation of fused crowned pyridine containing expanded porphyrins, and the macrocycles showed simple, well-resolved NMR spectra where all resonances were identified easily by 2D NMR spectroscopy. The macrocycles exhibited typical nonaromatic absorption features and showed one broad band with peak maxima at 535 nm and one or two shoulder bands in the higher energy region. The protonation studies resulted in clear colour change from purple to blue and absorption bands experienced bathochromic shifts with a broad band at 662 nm which was extended up to 800 nm. The electrochemical studies revealed that the macrocycles were easier to oxidize but difficult to reduce. DFT studies indicated that the macrocycle attains a very puckered and distorted 'U' shaped structure owing to the flexibility of the crown ether chain and TD-DFT studies corroborated experimental results. The preliminary studies indicated that the macrocycles could be used as colorimetric optical sensor for the detection of Cu2+ ion.

Absorption Spectra and the Electronic Structure of Gallic Acid in Water at Different pH: Experimental Data and Theoretical Cluster Models.

Gallic acid (GA) has been characterized in terms of its optical properties in aqueous solutions at varying pH in experiments and in theoretical calculations by analyzing the protonated and deprotonated forms of GA. This work is part of a series of studies of the optical properties of different carboxylic acids in aqueous media. The experimental electronic spectra of GA exhibit two strong well-separated absorption peaks (B- and C-bands), which agree with previous studies. However, in the current study, an additional well-defined low-energy shoulder band (A-band) in the optical spectra of GA was identified. It is likely that the A-band occurs for other carboxylic acids in solution, but because it can overlap with the B-band, it is difficult to discern. The theoretical calculations based on density functional theory were used to simulate the optical absorption spectra of GA in water at different pH to prove the existence of this newly found shoulder band and to describe and characterize the full experimental optical spectra of GA. Different cluster models were tested: (i) all water molecules are coordinated near the carboxy-group and (ii) additional water molecules near the hydroxy-groups of the phenyl ring were included. In this study, we found that both the polarizable continuum model (dielectric property of a medium) and neighboring water molecules (hydrogen-bonding) play significant roles in the optical spectrum. The results showed that only an extended cluster model with water molecules near carboxy- and hydroxy-groups together with the polarizable continuum model allowed us to fully reproduce the experimental data and capture all three absorption bands (A, B, and C). The oscillator strengths of the absorption bands were obtained from the experimental data and compared with theoretical results. Additionally, our work provides a detailed interpretation of the pH effects observed in the experimental absorption spectra.

Multiresponsive Tetra-Arylethene-Based Fluorescent Switch with Multicolored Changes: Single-Crystal Photochromism, Mechanochromism, and Acidichromism

In this article, we report a simple tetra-arylethene-based fluorescent switch TPS═C4 modified with a flexible alkyl chain by the Schiff base structure. The incorporation of C═N retains the excellent photochromic property of tetra-arylethene and endows TPS═C4 with new multiresponsiveness of mechanochromism and acidichromism and multicolor changes. TPS═C4 shows remarkable mechanochromism from a deep blue emission at 420 nm to bright blue with a new shoulder band at 450 nm, which arises from the force-induced phase transition from the crystal state to an amorphous form. Both the original crystalline powder and the ground amorphous sample exhibit interesting acidichromism, and their emission colors turn yellow (530 nm), due to the protonation of C═N. More interestingly, TPS═C4 displays fascinating photochromism in multiple states, especially in the single-crystal state. The flexible alkyl chain offers enough free space for molecular motion and facilitates single-crystal photochromism. Due to the multiresponsiveness and multicolor switch, TPS═C4 can be satisfactorily used for the multidimensional anticounterfeiting application. To the best of our knowledge, TPS═C4 is a rare multifunctional molecule with a simple structure but featuring multiresponsiveness and multicolor switch.

Multiple-H-bonded-zwitterionic tetramer structure for L-(+)-2-chlorophenylglycine, as investigated by UV, IR and Raman spectroscopy and electronic structure calculations

A DFT tetramer model constructed of multi-H-bonds at B3LYP/6-311G(d,p) level has been proposed for L-(+)-2-Chlorophenylglycine. Motivation in part for the tetramer model comes from the observed IR spectra near 3400−2500 cm−1 showing a very broad sub-band structure spread over ∼ 900 cm−1 without distinct sharp bands; secondly, XRD structures of similar molecular solids show multiple H-bonds among monomers. Therefore, the proposed tetramer consists of fourteen H-bonds arising from a network of inter-/intra-molecularly X−H···Y bonds: N−H···O, C−H···O and Cα−H···Cl bonds, all from four monomer species. The strengths and degree of these H-bonds being covalent, ionic or partial have been determined using topological parameters from AIM calculations. Other weaker van der Waals interactions and steric clashes in relation to the N−H···O, C−H···O and Cα−H···Cl bonds have also been evaluated by the method of ‘non-covalent interactions (NCI)’. Further, the charge transfer from the Y lone pair orbital (donor) to the X−H anti-bonding orbital (acceptor) have been explained on the basis of overlapping of orbitals using NBO analysis. Computed stabilization energies for the X−H···Y bonds have shown the inter-molecular N−H···O bonds to be the strongest of the H-bonds. Concentration-dependent UV spectral analysis aided by TD-DFT-based calculations at B3LYP/6-311G(d,p) with SMD model in water has shown that a strong band at 221 nm, among other bands, blue-shifts to 194 nm with a concomitant arrival of a shoulder band at 219 nm. The bands are assigned to the π→π* transition. This observation has been interpreted to be the result of dissociation of the tetrameric species into monomeric species and is supported by the stabilization of computed ground and excited electronic levels. By the same interpretation, three vibronic bands seen at 260−280 nm also have been explained. Computed vibrational modes of the tetramer fit very well with the experimental IR and Raman band features including low frequency Raman modes below 350 cm−1. It has been shown the consistency among the H-bonding descriptors - H···Y bond distance, change in X−H bond length, X−H frequency shifts, electron density, H-bond energy and stabilization energy by graphical correlations.

Improving the Solubility of Hexanuclear Heterometallic Extended Metal Atom Chain Compounds in Nonpolar Solvents by Introducing Alkyl Amine Moieties.

The highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) interaction at the dz2 orbital between two kinds of metal complex is useful for obtaining heterometallic one-dimensional (1D) chains as well as heterometallic metal string compounds (HMSCs). Platinum dinuclear complexes, [Pt2(piam)2(NH2R)4]X2 (piam = pivalamidate, R = CH3, C2H5, C3H7, or C4H9, X = anion), comprising σ* as HOMO were mixed with [Rh2(O2CCH3)4] comprising σ* as LUMO in solvents to afford single crystals of [{Rh2(O2CCH3)4}{Pt2(piam)2(NH2R)4}2]X4 (2–5). Single-crystal X-ray analyses revealed that 2–5 are hexanuclear complexes that are one-dimensionally aligned as Pt–Pt–Rh–Rh–Pt–Pt with metal–metal bonds, where the alkyl moieties at end Pt atoms obstruct further 1D extension. Complexes 2–5 appear as if they are cut off from an infinite chain [{Rh2(O2CCH3)4}{Pt2(piam)2(NH3)4}2]n(PF6)4n·6nH2O (1) aligned as −{Pt–Pt–Rh–Rh–Pt–Pt}n–. The diffuse reflectance spectrum of 1 depicts broad shoulder bands, which are not present in the spectra of 2–5, proving that the infinite chain 1 forms a band structure. Compounds 4 and 5 with propyl or butyl moieties at amine ligands, respectively, are soluble in nonpolar solvents, such as CH2Cl2, without the dissociation of their hexanuclear structures. Taking advantage of their solubility, measurement of cyclic voltammetry in CH2Cl2 become possible, which shows the quasi-reversible oxidation and reduction waves at 4: Eox = 0.86 V and Ered = 0.69 V and 5: Eox = 0.87 V and Ered = 0.53 V.

Estimation of leaf water content from hyperspectral data of different plant species by using three new spectral absorption indices.

The leaf equivalent water thickness (EWT, g cm−2) and fuel moisture content (FMC, %) are key variables in ecological and environmental monitoring. Although a variety of hyperspectral vegetation indices have been developed to estimate the leaf EWT and FMC, most of these indices are defined considered two or three specific bands for a specific plant species, which limits their applicability. In this study, we proposed three new spectral absorption indices (SAI970, SAI1200, and SAI1660) for various plant types by considering the symmetry of the spectral absorption at 970 nm, 1200 nm and 1660 nm and spectral heterogeneity of different leaves. The indices were calculated considering the absorption peak and shoulder bands of each leaf instead of the same specific bands for all leaves. A pooled dataset of three tree species (camphor (VX), capricorn (VJ), and red-leaf plum (VL)) was used to test the performance of the SAIs in terms of the leaf EWT and FMC estimation. The results indicated that, first, SAI1200 was more suitable for estimating the EWT than FMC, whereas SAI970 and SAI1660 were more suitable for estimating the FMC. Second, SAI1200 achieved the most accurate estimation of the EWT with a cross-validation coefficient of determination (Rcv2) of 0.845 and relative cross-validation root mean square error (rRMSEcv) of 8.90%. Third, SAI1660 outperformed the other indices in estimating the FMC at the leaf level, with an Rcv2 of 0.637 and rRMSEcv of 8.56%. Fourth, SAI970 achieved a moderate accuracy in estimating the EWT (Rcv2 of 0.25 and rRMSEcv of 19.68%) and FMC (Rcv2 of 0.275 and rRMSEcv of 12.10%) at the leaf level. These results can enrich the application of the SAIs and demonstrate the potential of using SAI1200 to determine the leaf EWT and SAI1660 to obtain the leaf FMC among various plant types.

Table sugar derived carbon nanodots for the extraction of bulk silver

Reducing nature of table sugar derived carbon dots, achieved via an economic and environmentally benign procedure is presented in the article. The as-synthesized carbon dots are adequately characterized using Transmission Electron Microscopy, X-Ray Diffraction analysis, as well as Fourier Transform Infra-Red, X-ray photoelectron, and Fluorescence spectroscopies. The particles possess average particle size of 3.8 nm, with UV absorption maximum at 245 nm, along with shoulder band around 320 nm. Bright cyan emission upon UV irradiation is also noted for the system. The commendable reducing nature of the system is illustrated through the conversion of Ag (I) to Ag(0) in bulk metallic form, via an extremely facile way.

Thermally Stable Nitrothiacalixarene Chromophores: Conformational Study and Aggregation Behavior.

Achieving high thermal stability and control of supramolecular organization of functional dyes in sensors and nonlinear optics remains a demanding task. This study was aimed at the evaluation of thermal behavior and Langmuir monolayer characteristics of topologically varied nitrothiacalixarene multichromophores and phenol monomers. A nitration/azo coupling alkylation synthetic route towards partially O-substituted nitrothiacalixarenes and 4-nitrophenylazo-thiacalixarenes was proposed and realized. Nuclear magnetic resonance (NMR) spectroscopy and X-ray diffractometry of disubstituted nitrothiacalix[4]arene revealed a rare 1,2-alternate conformation. A synchronous thermal analysis indicated higher decomposition temperatures of nitrothiacalixarene macrocycles as compared with monomers. Through surface pressure/potential-molecular area measurements, nitrothiacalixarenes were shown to form Langmuir monolayers at the air–water interface and, through atomic force microscopy (AFM) technique, Langmuir–Blodgett (LB) films on solid substrates. Reflection-absorption spectroscopy of monolayers and electronic absorption spectroscopy of LB films of nitrothiacalixarenes recorded a red-shifted band (290 nm) with a transition from chloroform, indicative of solvatochromism. Additionally, shoulder band at 360 nm was attributed to aggregation and supported by gas-phase density functional theory (DFT) calculations and dynamic light scattering (DLS) analysis in chloroform–methanol solvent in the case of monoalkylated calixarene 3. Excellent thermal stability and monolayer formation of nitrothiacalixarenes suggest their potential as functional dyes.

Reductive methylation of triphthaloylbenzene: Isolation and characterization of hexamethoxy-trinaphthylene and two unexpected trinaphthylene derivatives

With the aim of developing new π-conjugated materials for application in electronics, the reductive methylation of triphthaloylbenzene is presented. Several new products are obtained: 5,6,11,12,17,18-hexamethoxy-trinaphthylene (1a) and two unexpected compounds, i.e., the corresponding monohydroxy-pentamethoxy-trinaphthylene (1b) and a peculiar trinaphtylene derivative (2) possessing hydroxy, methoxy, carbonyl, and ketal groups and a tetrahydrofuran moiety fused on the core. X-ray crystallographic analysis of 1b and 2 reveals that both compounds exhibit deformed frameworks. The investigation of their optical properties shows that the lowest-energy absorption bands for 1a and 1b are a shoulder band around 350 nm, whereas 2 gives rise to a one broad and weak band at 573 nm. All the molecules have negligible fluorescence. Addition of 1,8-diazabicyclo[5.4.0]undec-7-ene into a solution of 2 causes a color change from purple to olive brown, which renders it suitable as a pH indicator.

Sintering Temperature Effect on the Luminescence Properties of Y2O3:Tb3+ Phosphors Synthesized using a Liquid-Phase Reaction

The photoluminescence properties of crystalline Y2O3:Tb3+ nanoparticles fabricated using a liquid-phase reaction have been examined over a certain sintering temperature range for dopant activation. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) were used to examine the size and the morphology of Y2O3:Tb3+ particles and disclosed the cubic Bragg peaks of the Y2O3:Tb3+ particles regardless of the sintering temperature with no substantial peak shift. The maximum photoluminescence (PL) emission intensity was observed from the Y2O3:Tb3+ phosphors sintered at 400 °C. The photoluminescence excitation (PLE) spectra of the Y2O3:Tb3+ phosphors are composed of broad bands at ∼260 nm (∼4.7 eV) and shoulder bands at ∼306 nm (∼4.05 eV). The experimental results revealed that the particle size and the crystallinity of the Y2O3:Tb3+ phosphors played a critical role in the luminescence. Over the entire range of sintering temperatures, the room-temperature decay time was found to be ∼2.81 ms.

Principal Vibration Modes of the La2O3-Ga2O3 Binary Glass Originated from Diverse Coordination Environments of Oxygen Atoms.

La2O3-Ga2O3 binary glass exhibits unusual optical properties owing to its high oxygen polarizability and low vibration energy. These optical properties include high refractive indices and a wide transmittance range. In this study, we performed classical molecular dynamics simulations on La2O3-Ga2O3 glass synthesized by an aerodynamic levitation technique. We have obtained structural models that reproduce experimental results, such as NMR, high-energy X-ray diffraction, and neutron diffraction. Based on our analysis, the structural features were clarified: 5-, 6-coordinated Ga, edge-sharing GaOx-GaOx polyhedral linkages, and oxygen triclusters. Additionally, the vibrational density of states was calculated by diagonalization of the dynamical matrix derived from the structural models and the results were compared with Raman scattering spectra. The mode analysis of the Raman spectra revealed that the principal bands at 650 cm-1 were mainly attributed to the stretching modes of the bridging and nonbridging oxygens. Meanwhile, the shoulder bands at the highest frequency of 750 cm-1 were mainly attributed to the stretching modes of the bridging oxygens and oxygen triclusters. The structural models obtained in this study well describe the characteristic local structures and vibrational properties of the La2O3-Ga2O3 glass.

Existence of weakly interacting OH bond at air/water interface.

Ab initio molecular dynamics simulations at the air/water interface are carried out and elucidate a clear bump-like shoulder band at ∼3600 cm-1 in the imaginary part of the second order nonlinear susceptibility measured by phase-sensitive or heterodyne-detected vibrational sum frequency generation spectroscopy. The structure of the weakly interacting (WI) OH bond producing this band is found by first-principles simulation. WI OH is the OH bond directing toward the vapor phase and is somewhat buried in the Gibbs dividing surface of water, which is a characteristic structure at the air/water interface. The WI OH vibration tends to couple with the combination band between a neighboring hydrogen-bonded OH vibration and its bonding intermolecular oxygen-oxygen vibration.