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Despite having practical applications in battery technology and serving as a model system for Fermi resonance coupling, ethylene carbonate (EC) receives little direct attention as a vibrational probe in nonlinear vibrational spectroscopy experiments. EC contains a Fermi resonance that is well-characterized in the linear spectrum, and the environmental sensitivity of its Fermi resonance peaks could make it a good molecular probe for two-dimensional infrared spectroscopy (2DIR) experiments. As a model system, we investigate the linear and 2DIR vibrational spectrum of the carbonyl stretching region of ethylene carbonate in tetrahydrofuran. The 2DIR spectrum reveals peak dynamics that evolve coherently. We characterize these dynamics in the context of Redfield theory and find evidence that EC dynamics proceed through coherent pathways, including singular coherence transfer pathways that have not been widely observed in other studies. We find that coherent contributions play a significant role in the observed dynamics of cross-peaks in the 2DIR spectrum, which must be accounted for to extract accurate measurements of early waiting time dynamics. [ABSTRACT FROM AUTHOR]

The hydration shells of phosphate ions and phosphate groups of nucleotides and phospholipid membranes display markedly different structures and hydrogen-bond strengths. Understanding phosphate hydration requires insight into the spatial arrangements of water molecules around phosphates and in thermally activated structure fluctuations on ultrafast time scales. Femtosecond two-dimensional infrared spectroscopy of phosphate vibrations, particularly asymmetric stretching vibrations between 1000 and 1200 cm−1, and ab initio molecular dynamics (AIMD) simulations are combined to map and characterize dynamic local hydration structures and phosphate–water interactions. Phosphoric acid H3PO4 and its anions H2PO4−, HPO42−, and PO43− are studied in aqueous environments of different pH value. The hydration shells of phosphates providing OH donor groups in hydrogen bonds with the first water layer undergo ultrafast structural fluctuations, which induce a pronounced spectral diffusion of vibrational excitations on a sub-300 fs time scale. With a decreasing number of phosphate OH groups, the hydration shell becomes more ordered and rigid. The 2D-IR line shapes observed with hydrated PO43− ions display a pronounced inhomogeneous broadening, reflecting a distribution of hydration geometries without fast equilibration. The AIMD simulations allow for an in-depth characterization of the hydration geometries with different numbers of water molecules in the first hydration layer and different correlation functions of the fluctuating electric field that the water environment exerts on the vibrational phosphate oscillators. [ABSTRACT FROM AUTHOR]

Dipole-bound states in anions exist when a polar neutral core binds an electron in a diffuse orbital through charge–dipole interaction. Electronically excited polar neutral cores can also bind an electron in a diffuse orbital to form Core-Excited Dipole-Bound States (CE-DBSs), which are difficult to observe because they usually lie above the electron detachment threshold, leading to very short lifetimes and, thus, unstructured transitions. We report here the photodetachment spectroscopy of cryogenically cooled acetylacetonate anion (C5H7O2−) recorded by detecting the neutral radical produced upon photodetachment and the infrared spectroscopy in He-nanodroplets. Two DBSs were identified in this anion. One of them lies close to the electron detachment threshold (∼2.74 eV) and is associated with the ground state of the radical (D0-DBS). Surprisingly, the other DBS appears as resonant transitions at 3.69 eV and is assigned to the CE-DBS associated with the first excited state of the radical (D1-DBS). It is proposed that the resonant transitions of the D1-DBS are observed ∼1 eV above the detachment threshold because its lifetime is determined by the internal conversion to the D0-DBS, after which the fast electron detachment takes place. [ABSTRACT FROM AUTHOR]

In this contribution, we investigate the formation and dissociation of boron–hydrogen (BH) pairs in crystalline silicon under thermal equilibrium conditions. Our samples span doping concentrations of nearly two orders of magnitude and are passivated with a layer stack consisting of thin aluminum oxide and hydrogen-rich silicon nitride (Al 2 O 3 /SiN x :H). This layer stack acts as a hydrogen source during a following rapid thermal annealing. We characterize the samples using low-temperature Fourier-transform infrared spectroscopy and four-point-probe resistivity measurements. Our findings show that the proportion of hydrogen atoms initially bound to boron (BH pairs) rises with increasing boron concentration. Upon isothermal dark annealing at (163 ± 2) °C, hydrogen present in molecular form, H 2 , dissociates at a rate directly proportional to the concentration of boron atoms, ∝ [ B − ], leading to the formation of BH pairs. With prolonged annealing, an unknown hydrogen complex is formed at a rate that is inversely proportional to the square of the boron concentration, ∝ 1/[B − ] 2 , resulting in the disappearance of BH pairs. Based on experimental observations, we derive a kinetic model in which we describe the formation of the unknown complex through neutral hydrogen H 0 binding to a sink. Additionally, we investigate the temperature dependence of the reaction rates and find that the H 2 dissociation process has an activation energy of (1.11 ± 0.05) eV, which is in close agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and temperature-programmed reaction/desorption have been employed to investigate the reaction of CH3–CHCl–C(=O)Cl on Cu (100), with the aid of density functional theory (DFT) calculations. Experimentally, CH3–CH=C=O (methylketene) is found to be the product from the dechlorination of CH3–CHCl–C(=O)Cl on Cu(100) at 120 K. The CH3–CH=C=O generated on the surface would dimerize to form 2,4-dimethylcyclobutane-1,3-dione below 180 K. In agreement with the experimental findings, our DFT molecular dynamics simulations demonstrate that the dechlorination of CH3–CHCl–C(=O)Cl, resulting in CH3–CH=C=O and two Cl atoms, occurs readily, completing within 0.6 ps at 300 K. The simulations also indicate that the cleavage of the CH–Cl bond precedes that of the C(=O)–Cl bond. The static DFT calculations suggest that the dimerization of CH3–CH=C=O primarily occurs through the coupling of two C=C bonds, which has a lower barrier of 38.08 kJ mol−1 compared to the 69.05 kJ mol−1 barrier for C=C + C=O coupling. [ABSTRACT FROM AUTHOR]

Poly(N,N-diethylacrylamide) (PdEA), one of the thermoresponsive polymers, in aqueous solutions has attracted much attention because of its characteristic properties, such as coil-to-globule (CG) transition. We performed two-dimensional infrared spectroscopy and molecular dynamics (MD) simulations to understand the hydration dynamics in the vicinity of the CG transition at the molecular level via vibrational frequency fluctuations of the carbonyl stretching modes in the side chains of PdEA. Furthermore, N,N-diethylpropionamide, a repeating monomer unit of PdEA, is also investigated for comparison. From decays of the frequency–frequency time correlation functions (FFTCFs) of the carbonyl stretching modes, we consider that inhomogeneity of the hydration environments originates from various backbone configurations of PdEA. The degree of the inhomogeneity depends on temperature. Hydration water molecules near the carbonyl groups are influenced by the confinements of the polymers. The restricted reorientation of the embedded water, the local torsions of the backbone, and the rearrangement of the whole structure contribute to the slow spectral diffusion. By performing MD simulations, we calculated the FFTCFs and dynamical quantities, such as fluctuations of the dihedral angles of the backbone and the orientation of the hydration water molecules. The simulated FFTCFs match well with the experimental results, indicating that the retarded water reorientations via the excluded volume effect play an important role in the vibrational frequency fluctuations of the carbonyl stretching mode. It is also found the embedded water molecules are influenced by the local torsions of the backbone structure within the time scales of the spectral diffusion. [ABSTRACT FROM AUTHOR]

Vibrational spectroscopy of protein structure often utilizes 13C18O-labeling of backbone carbonyls to further increase structural resolution. However, sidechains such as arginine, aspartate, and glutamate absorb within the same spectral region, complicating the analysis of isotope-labeled peaks. In this study, we report that the waiting time between pump and probe pulses in two-dimensional infrared spectroscopy can be used to suppress sidechain modes in favor of backbone amide I′ modes based on differences in vibrational lifetimes. Furthermore, differences in the lifetimes of 13C18O-amide I′ modes can aid in the assignment of secondary structure for labeled residues. Using model disordered and β-sheet peptides, it was determined that while β-sheets exhibit a longer lifetime than disordered structures, amide I′ modes in both secondary structures exhibit longer lifetimes than sidechain modes. Overall, this work demonstrates that collecting 2D IR data at delayed waiting times, based on differences in vibrational lifetime between modes, can be used to effectively suppress interfering sidechain modes and further identify secondary structures. [ABSTRACT FROM AUTHOR]

Ion pair formation is a fundamental molecular process that occurs in a wide variety of systems, including electrolytes, biological systems, and materials. In solution, the thiocyanate (SCN−) anion interacts with cations to form contact ion pairs (CIPs). Due to its ambidentate nature, thiocyanate can bind through either its sulfur or nitrogen atoms, depending on the solvent. This study focuses on the binding nature of thiocyanate with lithium ions as a function of the solvents using FTIR, 2D infrared spectroscopy (2DIR) spectroscopies, and theoretical calculations. The study reveals that the SCN− binding mode (S or N end) in CIPs can be identified through 2DIR spectroscopy but not by linear IR spectroscopy. Linear IR spectroscopy shows that the CN stretch frequencies are too close to one another to separate N- and S-bound CIPs. Moreover, the IR spectrum shows that the S–C stretch presents different frequencies for the salt in different solvents, but it is related to the anion speciation rather than to its binding mode. A similar trend is observed for the anion bend. 2DIR spectra show different dynamics for N-bound and S-bound thiocyanate. In particular, the frequency–frequency correlation function (FFCF) dynamics extracted from the 2DIR spectra have a single picosecond exponential decay for N-bound thiocyanate and a biexponential decay for S-bound thiocyanate, consistent with the binding mode of the anion. Finally, it is also observed that the binding mode also affects the line shape parameters, probably due to the different molecular mechanisms of the FFCF for N- and S-bound CIPs. [ABSTRACT FROM AUTHOR]

The supra-molecular structure of a liquid is strongly connected to its dynamics, which in turn control macroscopic properties such as viscosity. Consequently, detailed knowledge about how this structure changes with temperature is essential to understand the thermal evolution of the dynamics ranging from the liquid to the glass. Here, we combine infrared spectroscopy (IR) measurements of the hydrogen (H) bond stretching vibration of water with molecular dynamics simulations and employ a quantitative analysis to extract the inter-molecular H-bond length in a wide temperature range of the liquid. The extracted expansivity of this H-bond differs strongly from that of the average nearest neighbor distance of oxygen atoms obtained through a common conversion of mass density. However, both properties can be connected through a simple model based on a random loose packing of spheres with a variable coordination number, which demonstrates the relevance of supra-molecular arrangement. Furthermore, the exclusion of the expansivity of the inter-molecular H-bonds reveals that the most compact molecular arrangement is formed in the range of ∼ 316 − 331 K (i.e., above the density maximum) close to the temperature of several pressure-related anomalies, which indicates a characteristic point in the supra-molecular arrangement. These results confirm our earlier approach to deduce inter-molecular H-bond lengths via IR in polyalcohols [Gabriel et al. J. Chem. Phys. 154, 024503 (2021)] quantitatively and open a new alley to investigate the role of inter-molecular expansion as a precursor of molecular fluctuations on a bond-specific level. [ABSTRACT FROM AUTHOR]

Ethane ( C 2 H 6 ) is anticipated to be the most stable compound within the carbon–hydrogen system under the 100 GPa pressure range. Nevertheless, the properties of ethane under pressure are still poorly documented. Here, we present a comprehensive study of the structural and vibrational properties of C 2 H 6 in a diamond anvil cell at pressures up to 150 GPa. To obtain detailed data, ethane single-crystal was grown in a helium pressure-transmitting medium. Utilizing single-crystal x-ray diffraction, the distortion mechanism between the tetragonal and monoclinic phases, occurring over the 3.2–5.2 GPa pressure range, is disclosed. Subsequently, no phase transition is observed up to 150 GPa. The accurately measured compression curve is compared to various computational approximations. The vibrational modes measured by Raman spectroscopy and infrared absorption are well identified, and their evolution is well reproduced by ab initio calculations. In particular, an unusual anticrossing phenomenon occurs near 40 GPa between a rocking and a stretching mode, likely attributable to intermolecular interactions through hydrogen bonding. [ABSTRACT FROM AUTHOR]

Superfluid helium nanodroplets are unique nanomatrices for the isolation and study of transient molecular species, such as radicals, carbenes, and ions. In this work, isomers of C3H4+ were produced upon electron ionization of propyne and allene molecules and interrogated via infrared spectroscopy inside He nanodroplet matrices. It was found that the spectrum of C3H4+ has at least three distinct groups of bands. The relative intensities of the bands depend on the precursor employed and its pickup pressure, which indicates the presence of at least three different isomers. Two isomers were identified as allene and propyne radical cations. The third isomer, which has several new bands in the range of 3100–3200 cm−1, may be the elusive vinylmethylene H2C=CH–CH+ radical cation. The observed bands for the allene and propyne cations are in good agreement with the results of density functional theory calculations. However, there is only moderate agreement between the new bands and the theoretically calculated vinylmethylene spectrum, which indicates more work is necessary to unambiguously assign it. [ABSTRACT FROM AUTHOR]

Small molecule inhibitors (SMIs) have been gaining attention in the field of area-selective atomic layer deposition (ALD) because they can be applied in the vapor-phase. A major challenge for SMIs is that vapor-phase application leads to a disordered inhibitor layer with lower coverage as compared to self-assembled monolayers, SAMs. A lower coverage of SMIs makes achieving high selectivity for area-selective ALD more challenging. To overcome this challenge, mechanistic understanding is required for the formation of SMI layers and the resulting precursor blocking. In this study, reflection adsorption infrared spectroscopy measurements are used to investigate the performance of aniline as an SMI. Our results show that aniline undergoes catalytic surface reactions, such as hydrogenolysis, on a Ru non-growth area at substrate temperatures above 250 °C. At these temperatures, a greatly improved selectivity is observed for area-selective TaN ALD using aniline as an inhibitor. The results suggest that catalytic surface reactions of the SMI play an important role in improving precursor blocking, likely through the formation of a more carbon-rich inhibitor layer. More prominently, catalytic surface reactions can provide a new strategy for forming inhibitor layers that are otherwise very challenging or impossible to form directly through vapor-phase application. [ABSTRACT FROM AUTHOR]

An IR–vacuum ultraviolet (VUV) ion-dip spectroscopy method is utilized to examine the IR spectrum of acetaldehyde oxide (CH3CHOO) in the overtone CH stretch (2νCH) spectral region. IR activation creates a depletion of the ground state population that reduces the VUV photoionization signal on the parent mass channel. IR activation of the more stable and populated syn-CH3CHOO conformer results in rapid unimolecular decay to OH + vinoxy products and makes the most significant contribution to the observed spectrum. The resultant IR–VUV ion-dip spectrum of CH3CHOO is similar to that obtained previously for syn-CH3CHOO using IR action spectroscopy with UV laser-induced fluorescence detection of OH products. The prominent IR features at 5984 and 6081 cm−1 are also observed using UV + VUV photoionization of OH products. Complementary theoretical calculations utilizing a general implementation of second-order vibrational perturbation theory provide new insights on the vibrational transitions that give rise to the experimental spectrum in the overtone CH stretch region. The introduction of physically motivated small shifts of the harmonic frequencies yields remarkably improved agreement between experiment and theory in the overtone CH stretch region. The prominent features are assigned as highly mixed states with contributions from two quanta of CH stretch and/or a combination of CH stretch with an overtone in mode 4. The generality of this approach is demonstrated by applying it to three different levels of electronic structure theory/basis sets, all of which provide spectra that are virtually indistinguishable despite showing large deviations prior to introducing the shifts to the harmonic frequencies. [ABSTRACT FROM AUTHOR]

Small anionic nickel clusters with ethanol are investigated with a combination of mass-selective infrared photodissociation spectroscopy in a molecular beam and density functional theory simulations at the BLYP/6-311g(d,p) and TPSSh/def2-TZVPP level. In this context, the O–H stretching vibration of the ethanol is analyzed to obtain information about the structural motif, the geometry of the metal core, and the spin state of the clusters. For the [Ni2(EtOH)]− and [Ni3(EtOH)]− clusters, we assign quartet states of motifs with a hydrogen bond from the ethanol to the linear nickel core. The aggregation of a further ethanol molecule, yielding the [Ni3(EtOH)2]− cluster, results in the formation of a cooperative hydrogen bond network between the nickel core and the two ethanol molecules. [ABSTRACT FROM AUTHOR]

The gas-phase rotational spectrum from 8 to 750 GHz and the high-resolution infrared (IR) spectrum of pyridazine (o-C4H4N2) have been analyzed for the ground and four lowest-energy vibrationally excited states. A combined global fit of the rotational and IR data has been obtained using a sextic, centrifugally distorted-rotor Hamiltonian with Coriolis coupling between appropriate states. Coriolis coupling has been addressed in the two lowest-energy coupled dyads (ν16, ν13 and ν24, ν9). Utilizing the Coriolis coupling between the vibrational states of each dyad and the analysis of the IR spectrum for ν16 and ν9, we have determined precise band origins for each of these fundamental states: ν16 (B1) = 361.213 292 7 (17) cm−1, ν13 (A2) = 361.284 082 4 (17) cm−1, ν24 (B2) = 618.969 096 (26) cm−1, and ν9 (A1) = 664.723 378 4 (27) cm−1. Notably, the energy separation in the ν16-ν13 Coriolis-coupled dyad is one of the smallest spectroscopically measured energy separations between vibrational states: 2122.222 (72) MHz or 0.070 789 7 (24) cm−1. Despite ν13 being IR inactive and ν24 having an impractically low-intensity IR intensity, the band origins of all four vibrational states were measured, showcasing the power of combining the data provided by millimeter-wave and high-resolution IR spectra. Additionally, the spectra of pyridazine-dx isotopologues generated for a previous semi-experimental equilibrium structure (reSE) determination allowed us to analyze the two lowest-energy vibrational states of pyridazine for all nine pyridazine-dx isotopologues. Coriolis-coupling terms have been measured for analogous vibrational states across seven isotopologues, both enabling their comparison and providing a new benchmark for computational chemistry. [ABSTRACT FROM AUTHOR]

Functionalization of perovskite nanocrystal surfaces with thiocyanate anions presents a transformative approach to enhancing stability and photoluminescence quantum yield (PLQY) through surface defect passivation. This study investigates the role of thiocyanate ligands in modifying the optoelectronic properties of CsPbBr3 nanocrystals. We employed ultrafast two-dimensional infrared spectroscopy to investigate the nature of the dynamic interaction of thiocyanate ligands with nanocrystal surfaces, providing insights into the mechanisms underlying the observed increase in PLQY and stability. Our analysis reveals that the thiocyanate ligands efficiently passivate the surface defects, thereby enhancing the PLQY and the stability of the treated nanocrystals. The spectroscopic evidence supports a model where thiocyanate binds to under-coordinated lead atoms, contributing to a stable nanocrystal surface with enhanced optoelectronic performance. This ligand-induced passivation mechanism advances our understanding of surface chemistry's role in optimizing nanomaterials for solar cell and LED applications. [ABSTRACT FROM AUTHOR]

Fluorescence-encoded infrared (FEIR) spectroscopy is a recently developed technique for solution-phase vibrational spectroscopy with detection sensitivity at the single-molecule level. While its spectroscopic information content and important criteria for its practical experimental optimization have been identified, a general understanding of the electronic and nuclear properties required for highly sensitive detection, i.e., what makes a molecule a "good FEIR chromophore," is lacking. This work explores the molecular factors that determine FEIR vibrational activity and assesses computational approaches for its prediction. We employ density functional theory (DFT) and its time-dependent version (TD-DFT) to compute vibrational and electronic transition dipole moments, their relative orientation, and the Franck–Condon factors involved in FEIR activity. We apply these methods to compute the FEIR activities of normal modes of chromophores from the coumarin family and compare these predictions with experimental FEIR cross sections. We discuss the extent to which we can use computational models to predict the FEIR activity of individual vibrations in a candidate molecule. The results discussed in this work provide the groundwork for computational strategies for choosing FEIR vibrational probes or informing the structure of designer chromophores for single-molecule spectroscopic applications. [ABSTRACT FROM AUTHOR]

β-Ga2O3 is an ultrawide bandgap semiconductor that is attracting much attention for applications in next-generation high-power, deep UV, and extreme-environment devices. Hydrogen impurities have been found to have a strong effect on the electrical properties of β-Ga2O3. This Tutorial is a survey of what has been learned about O–H centers in β-Ga2O3 from their vibrational properties. More than a dozen, O–H centers have been discovered by infrared absorption spectroscopy. Theory predicts defect structures with H trapped at split configurations of a Ga(1) vacancy that are consistent with the isotope and polarization dependence of the O–H vibrational spectra that have been measured by experiment. Furthermore, O–H centers in β-Ga2O3 have been found to evolve upon thermal annealing, giving defect reactions that modify conductivity. While much progress has been made toward understanding the microscopic properties and reactions of O–H centers in β-Ga2O3, many questions are discussed that remain unanswered. A goal of this Tutorial is to inspire future research that might solve these puzzles. [ABSTRACT FROM AUTHOR]

We describe Reflection Absorption Infrared Spectroscopy (RAIRS) and first-principles Density Functional Theory (DFT) studies of ammonia adsorption on the Cu{311} surface. Our experimental results indicate an upright chemisorbed species at low coverages, with at least one additional species accompanying this at higher coverages. Our high-coverage RAIRS data cannot be fully explained by DFT models containing only ammonia or its dissociation products, even allowing for molecular tilt and/or the formation of a bilayer. We therefore also consider urea and formamide as possible products of surface reaction with residual carbon monoxide, but these species are again not fully compatible with our observed spectra. The overlayer composition at high coverages remains mysterious. [ABSTRACT FROM AUTHOR]

Doubly resonant sum frequency generation (DR-SFG) serves as a potent characteristic technique for probing the electronic spectra and vibronic coupling of molecules on surfaces. In this study, we successfully developed a novel infrared (IR)–white light (WL) DR-SFG spectroscopy based on narrowband IR and tunable broadband WL. This novel method was employed to explore the excitation spectrum and vibronic couplings of sub-monolayer Rhodamine 6G molecules. Our findings elucidate that the xanthene skeleton vibrational modes exhibit strong coupling with the S0–S1 electronic transition. Notably, we observed not only the 0–0 transition of the S0–S1 electronic continuum but also the 0–1 transition, a first time observation in the realm of DR-SFG spectroscopy. This advanced DR-SFG spectroscopy methodology facilitates a more sensitive examination of electronic spectra and the coupling between electronic transitions and vibrational modes, heralding a significant advancement in the understanding of molecular interactions on surfaces. [ABSTRACT FROM AUTHOR]

The α-hydroxyethyl radical (CH3·CHOH, 2A) is a key intermediate in ethanol biochemistry, combustion, atmospheric chemistry, radiation chemistry, and astrochemistry. Experimental data on the vibrational spectrum of this radical are crucially important for reliable detection and understanding of the chemical dynamics of this species. This study represents the first detailed experimental report on the infrared absorption bands of the α-hydroxyethyl radical complemented by ab initio computations. The radical was generated in solid para-H2 and Xe matrices via the reactions of hydrogen atoms with matrix-isolated ethanol molecules and radiolysis of isolated ethanol molecules with x rays. The absorption bands with maxima at 3654.6, 3052.1, 1425.7, 1247.9, 1195.6 (1177.4), and 1048.4 cm−1, observed in para-H2 matrices appearing upon the H· atom reaction, were attributed to the OHstr, α-CHstr, CCstr, COstr + CCObend, COstr, and CCstr + CCObend vibrational modes of the CH3·CHOH radical, respectively. The absorption bands with the positions slightly red-shifted from those observed in para-H2 were detected in both the irradiated and post-irradiation annealed Xe matrices containing C2H5OH. The results of the experiments with the isotopically substituted ethanol molecules (CH3CD2OH and CD3CD2OH) and the quantum-chemical computations at the UCCSD(T)/L2a_3 level support the assignment. The photolysis with ultraviolet light (240–300 nm) results in the decay of the α-hydroxyethyl radical, yielding acetaldehyde and its isomer, vinyl alcohol. A comparison of the experimental and theoretical results suggests that the radical adopts the thermodynamically more stable anti-conformation in both matrices. [ABSTRACT FROM AUTHOR]

Developing fluorescence-encoded infrared (FEIR) vibrational spectroscopy for single-molecule applications requires a detailed understanding of how the molecular response and external experimental parameters manifest in the detected signals. In Paper I [L. Whaley-Mayda, A. Guha, and A. Tokmakoff, J. Chem. Phys. 159, 194201 (2023)] we introduced a nonlinear response function theory to describe vibrational dynamics, vibronic coupling, and transition dipole orientation in FEIR experiments with ultrashort pulses. In this second paper, we apply the theory to investigate the role of intermode vibrational coherence, the orientation of vibrational and electronic transition dipoles, and the effects of finite pulse durations in experimental measurements. We focus on measurements at early encoding delays—where signal sizes are largest and therefore of most value for single-molecule experiments, but where many of these phenomena are most pronounced and can complicate the appearance of data. We compare experiments on coumarin dyes with finite-pulse response function simulations to explain the time-dependent behavior of FEIR spectra. The role of the orientational response is explored by analyzing polarization-dependent experiments and their ability to resolve relative dipole angles in the molecular frame. This work serves to demonstrate the molecular information content of FEIR experiments, and develop insight and guidelines for their interpretation. [ABSTRACT FROM AUTHOR]

Fluorescence-encoded infrared (FEIR) spectroscopy is an emerging technique for performing vibrational spectroscopy in solution with detection sensitivity down to single molecules. FEIR experiments use ultrashort pulses to excite a fluorescent molecule's vibrational and electronic transitions in a sequential, time-resolved manner, and are therefore sensitive to intervening vibrational dynamics on the ground state, vibronic coupling, and the relative orientation of vibrational and electronic transition dipole moments. This series of papers presents a theoretical treatment of FEIR spectroscopy that describes these phenomena and examines their manifestation in experimental data. This first paper develops a nonlinear response function description of Fourier-transform FEIR experiments for a two-level electronic system coupled to multiple vibrations, which is then applied to interpret experimental measurements in the second paper [L. Whaley-Mayda et al., J. Chem. Phys. 159, 194202 (2023)]. Vibrational coherence between pairs of modes produce oscillatory features that interfere with the vibrations' population response in a manner dependent on the relative signs of their respective Franck–Condon wavefunction overlaps, leading to time-dependent distortions in FEIR spectra. The orientational response of population and coherence contributions are analyzed and the ability of polarization-dependent experiments to extract relative transition dipole angles is discussed. Overall, this work presents a framework for understanding the full spectroscopic information content of FEIR measurements to aid data interpretation and inform optimal experimental design. [ABSTRACT FROM AUTHOR]

Phenylpropiolic acid (C6H5C≡CCOOH, PPA) isolated in nitrogen and xenon cryogenic matrices was studied by infrared spectroscopy. The experimental studies were complemented by a series of quantum chemical calculations carried out at the density functional theory (B3LYP) and MP2 levels of theory (with different basis sets). The calculations predicted the existence of two planar PPA conformers, differing in the arrangement of the carboxylic group. The higher-energy trans-PPA conformer has a negligible population in the gas phase at room temperature and was prepared in situ in the N2 cryomatrix through vibrationally-induced rotamerization of the lower-energy cis-PPA conformer, achieved using selective narrowband infrared excitation of the OH stretching coordinate of the latter species. Broadband UV (λ > 235 nm) irradiation of matrix-isolated cis-PPA was also undertaken, leading to the observation of cis-PPA → trans-PPA isomerization. No other UV-induced photoreactions were observed. The in situ generated trans-PPA conformer was found to decay back to cis-PPA in the dark by tunneling, and its lifetimes under different experimental conditions were determined. The assignment of the infrared spectra of both conformers is presented, considerably extending the vibrational information available on this molecule. [ABSTRACT FROM AUTHOR]

We present an IR-PD study of tantalum cluster adsorbate complexes [Tan(N2)m]+, abbreviated (n,m), n = 5–8. We utilize infrared spectroscopy of isolated and size selected clusters as prepared and characterized by a cryogenic tandem ion trap setup, and we augment our experiments with quantum chemical simulations at the level of density functional theory. The cluster adsorbate complexes (n,m) reveal vibrational bands above 2000 cm−1, which indicate end-on coordinated μ1-N2 oscillators, and bands below 2000 cm−1, which indicate side-on μ2-κN:κN,N coordinated ones. We observe a general increase in spectral complexity and an inhomogeneous broadening, mainly towards the red, at certain points of N2 loading m, which originates from an increasingly higher amount of double and triple N2 coordination at Ta sites, eventually at all of them. Other than the small tantalum clusters Tan+, n = 2–4, the IR-PD spectra of the initial N2 adsorbate species (n,1), n = 5–8, provide strong evidence for a lack of spontaneous N2 cleavage. Spontaneous N2 cleavage by Tan+, n = 5–8, seems suppressed. Therefore, the ability of a small Ta cluster to cleave dinitrogen disappears with one more tantalum core atom. The study of stepwise N2 adsorption on size selected Tan+, n = 5–8 clusters revealed adsorption limits m(max) of [Tan(N2)m]+ that are independent of cluster size within this size range. Cryo-adsorption kinetics at 26 K allowed for kinetic fits to consecutive N2 adsorption steps, and the fits revealed significant N2 desorption rates upon higher N2 loads, and the cluster adsorbate complexes eventually reached equilibrium. Some enhanced N2 desorption rates point towards likely adsorbate shell reorganization, and there is also some evidence for the coexistence of isomeric cluster adsorbate complexes. [ABSTRACT FROM AUTHOR]

We present an IR-PD study of tantalum cluster adsorbate complexes [Tan(N2)m]+, abbreviated (n,m), n = 5–8. We utilize infrared spectroscopy of isolated and size selected clusters as prepared and characterized by a cryogenic tandem ion trap setup, and we augment our experiments with quantum chemical simulations at the level of density functional theory. The cluster adsorbate complexes (n,m) reveal vibrational bands above 2000 cm−1, which indicate end-on coordinated μ1-N2 oscillators, and bands below 2000 cm−1, which indicate side-on μ2-κN:κN,N coordinated ones. We observe a general increase in spectral complexity and an inhomogeneous broadening, mainly towards the red, at certain points of N2 loading m, which originates from an increasingly higher amount of double and triple N2 coordination at Ta sites, eventually at all of them. Other than the small tantalum clusters Tan+, n = 2–4, the IR-PD spectra of the initial N2 adsorbate species (n,1), n = 5–8, provide strong evidence for a lack of spontaneous N2 cleavage. Spontaneous N2 cleavage by Tan+, n = 5–8, seems suppressed. Therefore, the ability of a small Ta cluster to cleave dinitrogen disappears with one more tantalum core atom. The study of stepwise N2 adsorption on size selected Tan+, n = 5–8 clusters revealed adsorption limits m(max) of [Tan(N2)m]+ that are independent of cluster size within this size range. Cryo-adsorption kinetics at 26 K allowed for kinetic fits to consecutive N2 adsorption steps, and the fits revealed significant N2 desorption rates upon higher N2 loads, and the cluster adsorbate complexes eventually reached equilibrium. Some enhanced N2 desorption rates point towards likely adsorbate shell reorganization, and there is also some evidence for the coexistence of isomeric cluster adsorbate complexes. [ABSTRACT FROM AUTHOR]

By inducing gamma radiation at a dose of 25 kGy, vinylpyrrolidone (VP) was combined with dioctyl sodium sulfosuccinate, an anionic surfactant, to create PVP@DSSS. The sorption and recovery of Ce(III) and Co(II) from aqueous solutions were evaluated using PVP@DSSS. The physical and chemical characterisation of prepared sorbent was investigated by X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and thermal analysis (TGA-DTA). The characterisations show that sorbents prepared using these techniques outperform conventional preparation methods. The PVP@DSSS was implanted for batch processing with the goal of studying the effect of different parameters on the sorption of the investigated metal ions, such as pH, contact time, metal ion concentration, and reaction temperatures. The results show that the maximum adsorption capacity of the PVP@DSSS adsorbent for Ce(III) and Co(III) were 9.8 and 0.9 mg/g, respectively. The adsorption of Ce(III) and Co(II) from aqueous suspension using PVP@DSSS was fit to Langmuir and pseudo second order equations well. The changes in the free energy (ΔG) and enthalpy (ΔH) values of Ce(III) confirm the endothermic nature of the adsorption reaction, whereas Co(II) adsorption was exothermic and spontaneous. The desorption efficiency was 95% for Co(II) and less than 10% for Ce(III) with HCl as good desorbing agent.The results show that PVP@DSSS is a promising adsorbent for the the recovery and separation process of Ce(III) ions from aqueous solution. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis of magnetic zeolite A using fly ash as the main sources of SiO₂ and Al₂O₃, by hydrothermal use in the adsorption of Pb2, Cd2, Zn2⁺ and Cu2. The composite synthesis was successful, and the obtained material was characterised by using different techniques, such as X-ray diffraction (XRD), X-ray fluorescence (XRF), Infrared vibrational spectroscopy (FTIR), Electron Microscopy (SEM), and pH point of zero charge (pHpzc). XRD measurements confirm zeolites A as the main crystalline phases (98.5%), with the presence of a small amount of sodalite (1.5%). In the SEM of magnetic composite, the characteristic morphology for zeolite A was noted, with magnetite nanoparticles dispersed on its surface, resulting in a composite with magnetic properties. In the adsorption study, the magnetic composite showed a fast rate of adsorption, in which the pseudo second order model was the one that best described the experimental data of the metal ions under study. The Redlich-Peterson isotherm model best represented the experimental data of Pb2⁺ and Cd2⁺, while the Langmuir and Sips models fitted Zn2⁺ and Cu2⁺, respectively. Thus, the results showed that the magnetic composite presented high magnetic quality, facilitating its separation from the aqueous medium, as well as being a promising adsorbent in the adsorption of metal ions in aqueous medium. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion disasters frequently appear in the process of coal mining, which brings great-hidden danger to mine safety production. To effectively inhibit coal spontaneous combustion, HPMC/PEG/CS thermosensitive hydrogels with quick phase-transition response times and excellent thermal stability have been developed in this study. Then, the effects of HPMC/PEG/CS thermosensitive hydrogel on microscopic groups of coal molecules at the corresponding temperature and coal spontaneous combustion heating processes are analyzed by using Fourier transform infrared spectrometry, temperature-programmed and thermogravimetric experiments. The results reveal that the gel skeleton shows porous structure and connects with each other, which improves the thermal stability and endothermic cooling capacity of the system. Compared with raw coal, the oxygen-containing groups and aliphatic hydrocarbon active groups of HPMC/PEG/CS thermosensitive hydrogel treated coal are decreased. In addition, the characteristic temperature point of CO rapid release is postponed, and its inhibition rate is 74.48%. Simultaneously, the apparent activation energy of different oxidation stages is increased. The characteristic temperature point of coal spontaneous combustion oxidation process is delayed, thus improving the difficulty of coal spontaneous combustion reaction. HPMC/PEG/CS thermosensitive hydrogels can inhibit coal spontaneous combustion reactions by reducing the activity of coal molecules and delaying the process of coal spontaneous combustion reactions through releasing water, absorbing heat, cooling, and covering oxygen. [ABSTRACT FROM AUTHOR]

A novel spectroscopic approach has been developed for laser absorption sensing of homonuclear diatomic molecules at high pressures relevant to modern energy devices. The spectroscopic approach exploits the collision-induced absorption (CIA) effect, wherein collisions between pairs or clusters of molecules generate transient electric dipole moments. This effect causes 'infrared inactive' molecules, including hydrogen (H 2) and nitrogen (N 2), to exhibit infrared absorption spectra at sufficiently high gas densities. The CIA spectra of the H 2 H 2 and N 2 N 2 pairs in the fundamental bands were experimentally studied up to 70 atm and found to be in close agreement with the HITRAN CIA database. Notably, the CIA spectra scale quadratically with gas density and are found to be 3 to 5 orders of magnitude stronger than their molecular spectra at elevated pressures. Additional measurements were made to accurately model CIA spectra with varying mixture compositions. These spectra enable a two-color fixed-wavelength direct-absorption strategy to simultaneously measure H 2 and N 2 in binary mixtures, targeting their fundamental CIA bands near 2. 1 μ m and 4. 3 μ m , respectively. A multi-pressure sensing strategy was further introduced to effectively separate CIA spectra from molecular interference by exploiting their distinct density dependencies. The measurements presented demonstrate a new infrared absorption spectroscopy approach that will enable direct and sensitive measurement of homonuclear diatomic molecules under conditions relevant to practical energy systems. • First direct infrared sensing of H 2 and N 2 via collision-induced absorption (CIA). • Room-temp CIA spectra of H 2 -H 2 , N 2 -N 2 , and H 2 -N 2 pairs studied up to 70 atm. • Two-color absorption approach measures H 2 and N 2 simultaneously target their CIA bands at 2335 & 4220 cm−1. • Multi-pressure strategy separates CIA spectra from molecular absorption spectra. • Introduce a new methodology for measuring homonuclear diatomic species in the infrared at high pressures. [ABSTRACT FROM AUTHOR]

Opuntia ficus-indica, also known as the prickly pear, is a cactus belonging to the Cactaceae family. For centuries, this remarkable plant has been valued for its medicinal, environmental, and culinary uses. The primary objective of this research is to examine and contrast the chemical composition, functional attributes, and nutritional significance of Opuntia ficus-indica cladodes sourced from three distinct regions in Morocco: Oulad Boubker, Imzouren, and Skoura. According to the results, moisture content differs significantly between the three sites, from 88.21 ± 0.20% to 92.11 ± 0.10%, with an acid pH value. While the ash content remained consistent across all three samples. Carbohydrate content ranging from 55.40 ± 0.08% to 55.90 ± 0.60%, fat content from 2.30 ± 0.21 to 2.62 ± 0.09, protein from 7.54 ± 0.03% to 9.07 ± 0.16%, crude fibers from 20.52 ± 1.87% to 21.00 ± 0.20%, and soluble fibers from 15.08 ± 0.16% to 16.33 ± 1.25%. Additionally, total chlorophyll content varied between 102.64 ± 8.93 and 144.80 ± 3.08 mg.100 g−1 DM. The functional properties showed considerable differences between the three samples: the water holding capacity ranged from 109.58 ± 0.11 to 174.95 ± 0.06 g water.100 g−1 DM, the oil holding capacity from 129.27 ± 0.39 to 146.51 ± 0.39 g oil.100 g−1 DM and the solubility index from 25.75 ± 0.60 to 33.18 ± 0.15 g solids.100 g−1 DM. Mineral analysis revealed significant differences based on location. The concentrations of potassium exhibited a considerable elevation compared to those of magnesium, calcium, sodium, iron, and zinc. Moreover, the existence of diverse organic functional entities, including alcohols, ketones, and acids, was authenticated by Fourier-transform infrared spectroscopy. A differential distribution of the chemical composition of cladodes according to region was confirmed by nutritional, mineral and functional characterization and functional groups of cladodes. [ABSTRACT FROM AUTHOR]

The CuO nanorods were in-situ grown on sensing electrodes by a chemical bath method for the detection of volatile organic compounds (VOCs). The synthesized material was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). The CuO nanorods, with lengths of 100–150 nm and diameters of 35–55 nm, were uniformly formed into a thin film on the electrode surface, with a thickness of approximately 1 μm. The gas test results demonstrated that the sensor achieved a peak response of 1.32 for formaldehyde at 200 °C, and a response of 1.92 for ethanol at 175 °C. At a concentration of 50 ppm, ethanol and formaldehyde at an operating temperature of 200 °C exhibit short response/recovery times of 28 s/48 s for ethanol and 45 s/62 s for methanol, respectively, coupled with good reproducibility. Moreover, the sensor exhibited a power-law response to varying gas concentrations and showcased superior selectivity in the VOCs gas detection. This in-situ growing CuO of our work provides a facial gas sensing material fabricated method. [ABSTRACT FROM AUTHOR]

The contamination of water resources in recent years has resulted in the dissemination of harmful bacteria via water sources, posing a significant threat to the safety and well-being of humans, animals, and plants. Consequently, there is a growing concern over the health and sanitation of water resources. Photocatalysis, a novel and very effective antibacterial method, has gained significant attention in the area of antibacterial research. Bismuth nitrate pentahydrate and sodium tungstate dihydrate were used in a straightforward hydrothermal process to create nanoflower spheres Bi 2 WO 6 /ZnO photocatalytic composites in molar ratios of 1:1, 1:2, 1:3, and 1:4. The first-ever demonstration of the photocatalytic broad-spectrum antibacterial activity of porous nanoflower spheres Bi 2 WO 6 /ZnO composites was shown. The samples were analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and ultraviolet–visible spectroscopy (UV–vis). The antibacterial activity was evaluated using the dilution coated plate technique, with LED light irradiation. The findings indicate that the Bi 2 WO 6 /ZnO composite has a much superior antibacterial activity against both bacteria and fungus compared to individual Bi 2 WO 6 and ZnO. When exposed to LED lighting with an intensity of 35 W, the Bi 2 WO 6 /ZnO nanoparticles in a 1:2 ratio at a concentration of 1000 mg/L demonstrated complete antibacterial effectiveness against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis within 30 min. Similarly, the nanoparticles achieved 100 % antibacterial efficiency against Candida albicans within 90 min. The antibacterial efficacy of 1000 mg/L 1:2 Bi 2 WO 6 /ZnO nanoparticles against Escherichia coli and Staphylococcus aureus was found to be 100 % within 5 min under natural lighting conditions. The findings indicate that Bi 2 WO 6 /ZnO nanoparticles have excellent photocatalytic broad-spectrum antibacterial efficacy. [ABSTRACT FROM AUTHOR]

Heat-resistant semi-aromatic poly (decamethylene terephthalamide) acid (PA10T) and a series of poly (decamethylene terephthalamide/decamethylene furanamide) (PA10T/10F) with a high content of bio-based carbon were synthesized by a cost-effective high-pressure solution polycondensation method. The chemical structures of the obtained samples were evaluated by Fourier infrared spectroscopy (FT-IR). Moreover, the effect of the addition of copolymer 2,5-furandicarboxylic acid (FDCA) and the copolymerization ratios of FDCA for PA10T on thermal performances, crystallization behaviors, and mechanical properties of PA10T and PA10T/10F were studied in detail. In addition, the results of DSC indicate that the melting points of PA10T/10F copolyamides can be adjusted appropriately by varying the feed ratios of FDCA, suggesting the improvement of processabilities. Besides, with increasing the copolymerization ratios of FDCA, the sizes of spherulites decreased gradually analyzed by POM. Furthermore, the results of XRD showed that the PA10T homopolymer and PA10T/10F copolyamides possess similar shapes around 2θ = 21°. In addition, compared with pure PA10T, the tensile strength, breaking elongation, bending strength, bending modulus, and izod impact strength all increased obviously when the feed ratio of FDCA and terephthalic acid (PTA) was 5:95. Therefore, the crystallization behaviors, processing performances, and mechanical characteristics of PA10T can be improved significantly by introducing FDCA, to improve the bio-based carbon content of PA10T and meet the increasing demand for environmentally friendly materials all over the world. [ABSTRACT FROM AUTHOR]

Objective: Today, there is only limited knowledge of the spatial organization of hair chemistry. Infrared microspectroscopy is a well‐established tool to provide such information and has significantly contributed to this field. In this study, we present new results combining multiple infrared microspectroscopy methods at different length scales to create a better chemical histology of human hair, including the hair follicle, hair shaft, hair medulla and hair cuticle. Methods: We used hyperspectral IR imaging & spectroscopy (HIRIS) and synchrotron‐radiation FTIR microspectroscopy (SR‐μFTIR) to measure transversal hair sections and SR‐μFTIR to obtain high‐resolution maps of longitudinal sections from the hair shaft and from the hair follicle. We used optical photothermal IR microspectroscopy (OPTIR) to analyse the cuticle surface of intact hairs. Results: By mapping longitudinal sections of the human hair follicle with confocal SR‐μFTIR, we report the first demonstration of glycogen presence in the outer root sheath of the hair follicle by spectroscopy, and its quantification at the micron scale. Spectral maps, combined with machine learning‐based analysis, enabled us to differentiate the various layers of the hair follicle and provided insights into the chemical changes that occur during hair formation in the follicle. Using HIRIS and SR‐μFTIR to analyse the hair medulla in transversal sections of human hairs, we report here, for the first time by vibrational spectroscopy methods, the detection of unsaturated lipids at very low concentrations in the medulla. By analysing longitudinal sections of the hair shaft with SR‐μFTIR, we found that calcium carboxylates are present in large regions of the hair cuticle, and not just in small focal areas as previously thought. We then use OPTIR to analyse the hair cuticle of intact hairs at submicron resolution without sectioning and report the distribution of calcium carboxylates at the surface of intact hair for the first time. Conclusion: These new findings illustrate the potential of infrared microspectroscopy for imaging the chemical composition of human hair and may have implications for biomedical research or cosmetology. [ABSTRACT FROM AUTHOR]

Drought is one of the main factors contributing to tree mortality worldwide and drought events are set to become more frequent and intense in the face of a changing climate. Quantifying water stress of forests is crucial in predicting and understanding their vulnerability to drought‐induced mortality. Here, we explore the use of high‐resolution spectroscopy in predicting water stress indicators of two native Australian tree species, Callitris rhomboidea and Eucalyptus viminalis. Specific spectral features and indices derived from leaf‐level spectroscopy were assessed as potential proxies to predict leaf water potential (Ψleaf), equivalent water thickness (EWT) and fuel moisture content (FMC) in a dedicated laboratory experiment. New spectral indices were identified that enabled very high confidence linear prediction of Ψleaf for both species (R2 > 0.85) with predictive capacity increasing when accounting for a breakpoint in the relationships using segmented regression (E. viminalis, R2 > 0.89; C. rhomboidea, R2 > 0.87). EWT and FMC were also linearly predicted to a high accuracy (E. viminalis, R2 > 0.90; C. rhomboidea, R2 > 0.80). This study highlights the potential of spectroscopy as a tool for predicting measures of plant water noninvasively, enabling broader applications for monitoring and managing plant water stress. Summary Statement: This study explored the use of proximal spectroscopy in predicting plant water stress indicators of two native Australian tree species. We derived new spectral indices that enabled very high prediction of leaf water potential, equivalent water thickness, and fuel moisture content. [ABSTRACT FROM AUTHOR]

In this study, α-Fe2O3/Fe3O4 nanocomposite (NC) coated with polyethylene glycol were synthesized via hydrothermal synthesis, achieving uniform particle formation and controlled crystallinity. Characterization using Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV–Vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDAX) confirmed the physical attributes and homogeneity of the nanocomposite. Polyethylene glycol-coated α-Fe2O3/Fe3O4 showed a reduced crystalline size of 19.13 nm compared to 22.93 nm for uncoated nanoparticles. Optical band gap measurements revealed values of 4.64 electron volts for polyethylene glycol, 1.98 electron volts for α-Fe2O3/Fe3O4 NC, and 3.18 electron volts for α-Fe2O3/Fe3O4@polyethylene glycol nanocomposites, indicating both insulating and semiconducting behaviors. The photocatalytic performance of the polyethylene glycol-coated α-Fe2O3/Fe3O4 was demonstrated by a 99.4% degradation of Brilliant Cresyl Blue (BCB) dye within 120 minutes at a concentration of 5 milligrams per milliliter, with a pseudo-first-order rate constant of 0.02047 per minute. Furthermore, the nanocomposites exhibited strong recyclability and reusability, making them viable candidates for environmental remediation. The study underscores the potential of α-Fe2O3/Fe3O4 NC in applications such as water treatment and antioxidant therapies. [ABSTRACT FROM AUTHOR]

A new approach is proposed to assess the degree of defect density of kaolinite minerals using their IR spectra in the OH-stretching vibration region. Three linear equations were obtained that relate the ratios of spectroscopic parameters to each other: + 1.247; + 2.8696; , where: FWHM(νi) is a full width at half maximum and A(νi) is the integral intensity of Lorentzian absorption bands at ν1 ~ 3697 cm–1, ν2 ~ 3670 cm–1, ν3 ~ 3652 cm–1 and ν4 ~ 3620 cm–1, respectively. These equations made it possible to establish criteria for decomposing the IR spectra into individual bands (νi) and determining the optimal values for the FWHM(νi) and A(νi) parameters used for calculating the contents of high-ordered kaolinite (HOK) and low-ordered kaolinite (LOK) phases in natural samples with an accuracy of ~5%. [ABSTRACT FROM AUTHOR]

In this study, the binary polymeric magnetic beads were synthesized successfully by one-pot polymerization of polyaniline (PA) doped magnetic iron oxide nanoparticles (MNPs) followed by chitosan (CTS) cross-linkage. The newly fabricated ternary magnetic beads (CTS@MPA) were applied to enhance the removal of Pb(II) and Cd(II) ions from the aqueous media. The prepared nanocomposite was characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometry (VSM). Adsorption experiments were carried out under optimum conditions. To evaluate the experimental data, the isotherm and kinetic models were conducted. The behavior of adsorption was assessed, and the coefficient of determination values demonstrated that the adsorption process best fitted the Freundlich model due to high values of R2 (0.957 & 0.981). The maximum adsorption capacity was obtained at 150.82 mg.g−1 and 169.21 mg.g−1 for Pb(II) and Cd(II) ions, respectively. Kinetic studies showed that adsorption follows a pseudo-second-order model (R2 = 0.952 & 0.985). Weber-Morris claims that intraparticle diffusion plays a significant role in the adsorption kinetics. Finally, the thermodynamic study is demonstrated, and the adsorption is endothermic, and the mechanism follows a physisorption pattern. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Electrochemical attenuated total reflection surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) plays an important role in deciphering interfacial reaction mechanisms at molecular level. However, the corrosive etching of Si internal reflection element by OH− largely impedes reliable SEIRAS measurements in strong alkaline electrolytes. Herein, a dense and chemically inert nanocrystalline diamond (NCD) film is successfully fabricated at a thickness of ~120 nm through hot filament chemical vapor deposition on a micromachined Si wafer to insulate the OH− etching. A reversible interfacial water feature without spectral interference of Si‐O band is obtained in 1.0 mol·L–1 KOH on Au/NCD/Si film electrode. Afterwards, electrochemical CO reduction reaction on Cu film electrode is explored in different KOH concentrations ranging from 0.1 to 3.0 mol·L–1 as a model reaction. A redshift of COL band, as well as its lower intensity but faster depletion kinetics, is noted with increasing electrolyte pH, whereas COB is identified as an inert spectator accumulating on Cu surface. Our present work demonstrates the alkaline resistant feature of diamond/Si composite internal reflection element, which could be a powerful platform to study electrocatalytic reactions in strong alkaline media. [ABSTRACT FROM AUTHOR]

To modify the physical features and extend applications of the 3-nitro-1,2,4-triazol-5-one (NTO), we synthesized NTO with acridine (ACR) at a molar ratio of 1:1, a neutralization reaction. Through altering the chemical composition, it was possible to alter physical properties such as thermal stability, free space (voids), packing coefficient, crystal density, difference in pKa of co-formers, morphology, solubility, and impact sensitivity, and detonation parameters. It appears that physical attributes could be entirely altered. Single-crystal and powder X-ray diffraction methods, infrared spectroscopy, mass spectrometry, nuclear magnetic resonance spectroscopy (1H-NMR and 13C-NMR), and thermal analysis were utilized to comprehensively characterize and confirm the formation of the structure of NTO:ACR. The substantial hydrogen bond interactions and planar layered structures observed between the cations and anions generated a complex 3D network, providing insight into the structure–property interrelationship. One intriguing feature discovered is the layered structure present in NTO:ACR, which may be responsible for the low impact sensitivity. According to the experimental results, NTO:ACR showed good thermal stability (Td = 229 °C) and outstanding impact sensitivity (IS = 100 J). Detonation velocity and pressure were calculated using the EXPLO5 software program and found to be 7006 m·s−1 and 20.02 GPa, respectively. [ABSTRACT FROM AUTHOR]

This study aimed to synthesize the emollient ester hexyl oleate by enzymatic catalysis using lipase G from Penicillium camemberti immobilized on the magnetic copolymer poly(styrene-co-triethylene glycol dimethacrylate) (STY-TEGDMA-M). For this, an experimental study was carried out on esterification reactions conducted in solvent-free medium, and the collected data were used to construct a mathematical model. The physical properties of the immobilized derivative were evaluated by scanning electron microscopy and Fourier-transform infrared spectroscopy. The results confirmed that lipase G was successfully immobilized onto the support, with a catalytic activity of 564.63 U g−1. The biocatalyst showed optimum performance at 45 °C, reaching 82% conversion after 48 h of reaction. A chromatographic method was used to confirm the formation of hexyl oleate. A thermal stability assay was conducted, showing that the biocatalyst retained 87% of its initial activity after 4 h of incubation at 60 °C. Mathematical modeling was based on the ping-pong bi-bi kinetic mechanism. The best model was selected according to the lowest value of the corrected Akaike information criterion (AICC = 124.776). The model revealed equilibrium constant values (Keq) ranging from 0.87 to 14.57, maximum rates of the forward reaction ranging from 0.088 to 0.090 mol L−1 min−1, and a maximum rate of the reverse reaction of 0.021 mol L−1 min−1. [ABSTRACT FROM AUTHOR]

This work aims to electrodeposit Cr from a solution containing only Cr3+ ions but not any other complexing, buffering and pH agents, and study its corrosion behavior. The solution was investigated by cyclic voltammetry and ultraviolet–visible spectroscopy. It was obtained that it is rich in native Cr complexes including Cl. Cr was successfully coated from this solution by binary potential loop electrodeposition. First, − 0.7 V potential was applied for a time interval ranging from 5 to 30 s. Then, a − 1.8 V potential was applied to deposit the Cr layer with the thickness changed from 50 to 1000 nm. X-ray diffraction patterns showed that all films are in a bcc crystal structure. The Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and optical profilometry measurements inferred that the coatings include hydrated-Cl complexes mostly edges of the coating and cracks. The scanning electron microscopy images indicated that the cracks on the surface are tiny for the layers thinner than 500 nm but prominent for the layers thicker than 500 nm. The corrosion behavior was examined by electrochemical impedance spectroscopy and Tafel measurements. The coatings electrodeposited by the binary potential loop had a corrosion rate lower and resistance higher than those of the coatings electrodeposited at − 1.8 V potential. The corrosion parameters became superior for the coatings with layers thinner than 500 nm and the aged ones. [ABSTRACT FROM AUTHOR]

Borosilicate glasses possess excellent melting properties and high stability against chemical attack by aqueous solutions, enabling this glass family to be used in various fields. In this article, we design a novel glass network in order to achieve a chemically robust glass with a low melting temperature. Therefore, the substitution effect of Na2O by MgO, Al2O3, Li2O, and K2O on the chemical durability and melting properties of sodium aluminosilicate glass (i.e., 80SiO2‒5Al2O3‒15Na2O [mol%]) was examined using a standard hydrolytic resistance test and viscosity measurement. Interestingly, we found that the partial replacement of Na2O by Al2O3, Li2O, and K2O (i.e., 80SiO2‒5Al2O3‒15Na2O → 80SiO2‒6.5Al2O3‒9Li2O‒2.25Na2O‒2.25K2O) makes the glass network with chemical durability and melting properties comparable to those of the commercial borosilicate network, resulting in a low HCl consumption of 0.04 mL/g and working temperature of 1238°C (i.e., temperature at viscosity 104 dPa s). The structural characterizations indicate that the high chemical stability of this glass composition originates from the abundance of SiO4 tetrahedrons with three and four bridging oxygen in the glass network as well as the increase in cationic field strength of mixed alkali ions. These excellent melting properties and superior chemical durability of glass imply the possibility of using the mixed alkali metal oxides aluminosilicate glass together with the commercial borosilicate glass in the markets for numerous practical applications. [ABSTRACT FROM AUTHOR]

Polytetrafluoroethylene (PTFE) is renowned for its remarkably low friction coefficient (µ ~ 0.1) yet exhibits notably high wear rates (K ~ 104) in dry sliding applications. To mitigate this, various metallic and non-metallic fillers have been explored, consistently demonstrating a reduction in wear rates of unfilled PTFE between 10 and 104 times. Among these fillers, α-Al2O3 is one of the most extensively studied materials. 5 wt% of α-Al2O3 filler into PTFE yields a composite material, PTFE- α-Al2O3, characterized by a wear rate a staggering 104 times lower than unfilled PTFE. This reduction in wear has been attributed to the formation of tribofilms on the PTFE composite and metal counterbody material. These tribofilms emerge due to the interaction between broken fluropolymer chains and environmental water and oxygen. This interaction results in the creation of carboxylate salt groups, which subsequently react with metal/metal oxide particles (both from the counterbody and the metal filler) to form tribofilms. Despite numerous studies scrutinizing the chemical composition of the tribofilms pre- and post-test, the chemical development of these films has remained largely unexplored. In this study, the authors utilize attenuated total reflection infrared spectroscopy (ATR-IR), transmission infrared (IR) spectroscopy, optical microscopy, and stylus profilometry to observe tribofilm development. A thorough topographical and chemical description of the tribofilm is provided via these techniques. The ratio of carboxylate salt groups directly corresponds with improved wear performance and these changes are very local to the worn polymer surface. This discovery contributes to a deeper understanding of the tribological behavior of PTFE-α-Al2O3 composites. [ABSTRACT FROM AUTHOR]

A nanocomposite consisting of graphene oxide (GO), cadmium sulfide (CdS), lead sulfide (PbS), and bismuth titanate (BT) was synthesized using the hydrothermal method. The structural and morphological characteristics of the nanocomposites were determined using various techniques. A shift in the x-ray diffraction peak positions of the GO-substituted samples indicates the successful integration of GO into the cadmium sulfide/bismuth titanate (CdS/BT) and lead sulfide/bismuth titanate (PbS/BT) matrices. The UV-visible spectra of the GO-reinforced bismuth Titanate show a decrease in the band gap of the nanocomposites. The presence of peaks at 1616 cm−1 and 954 cm−1 in the Fourier-transform infrared spectroscopy spectra confirms the incorporation of GO into the CdS/BT and PbS/BT samples. The photocatalytic performance of the materials was assessed through water-splitting experiments using methanol as a sacrificial agent. The results indicate that the GO composite with PbS/BT samples achieved the highest hydrogen production yield, measuring 438.21 μmolg−1. [ABSTRACT FROM AUTHOR]

The change in the behavior of pristine cobalt ferrite on doping it with rare-earth (RE) metal ions has been investigated. The CoFe2-xDyxO4 (where x = 0–0.1, with stepsize of 0.02) nanomaterials were synthesized by the co-precipitation method and corresponding morphological, structural, optical, and magnetic properties were observed. The x-ray diffraction (XRD) spectra revealed that all the prepared samples show a crystalline nature and that the crystallite size reduces with increasing dysprosium (Dy) concentration from 21 to 9 nm for x = 0.02 to x = 0.1. The Fourier-transform infrared spectroscopy (FTIR) spectra in the 4000–400 cm−1 range supported the material formation. Diffused reflectance spectroscopy (DRS) was used for the energy bandgap calculation. Field-emission scanning electron microscopy (FESEM)–energy dispersive x-ray spectroscopy (EDAX) spectra showed the surface morphology and elemental composition of the materials and no peaks corresponding to other elements were observed. Room-temperature Vibrating sample magnetometer (VSM) studies at a field of 7 T revealed that the sample with x = 0.02 had the highest value of saturation magnetization at 77.39 emu/g, which is even greater than the CoFe2O4 sample, while the sample composition x = 0.1 had the least saturation magnetization of 36.41 emu/g. This reduction was brought on by the lower magnetic interactions between the RE3+ and Fe3+ ions. Such materials can have applications in optoelectronic, magnetic hyperthermia, and high-frequency devices. [ABSTRACT FROM AUTHOR]

This study focuses on the synthesis and characterization of La9.33Si6O26:Tb3+ phosphor produced through the sol–gel method. The structural analysis conducted using x-ray diffraction confirmed a hexagonal apatite crystal structure with the P63/m space group. The functional groups were analyzed using Fourier-transform infrared spectroscopy. Scanning electron microscopy images displayed uniform spherical particles. Photoluminescence (PL) studies revealed strong excitation and emission properties, with distinct peaks corresponding to the spin-allowed and spin-forbidden transitions of Tb3+ ion. The PL excitation spectra, measured at an emission wavelength (λem) of 543 nm, exhibited a significant peak at 230 nm attributed to the 4f–5d spin-allowed transition of Tb3+ ions, splitting into a band at 274 nm due to spin-forbidden 4f–4f transitions. The emission spectra, excited (λexc) at 274 nm, displayed multiple peaks in the blue region at 420 nm, 438 nm, 452 nm, and 470 nm, corresponding to the 5D3 → 7F5, 5D3 → 7F4, 5D3 → 7F3, and 5D3 → 7F2 transitions, respectively. Additionally, peaks in the 480- to 650-nm segment indicated different transitions, showing the efficiency of the host lattice. The prominent emission peaks at 490 nm (5D4 → 7F6), 543 nm (5D4 → 7F5), 585 nm (5D4 → 7F4), and 622 nm (5D4 → 7F3) are due to the transition of Tb3+ ion. The peak at 543 nm, corresponding to the 5D4 → 7F5 transition, is particularly intense, resulting in a bright green luminescence visible to the naked eye under UV excitation. Vacuum PL measurements confirmed the green emission characteristics of the synthesized La9.33Si6O26:xTb3+ phosphors, indicating stable and intense green luminescence. These properties make them ideal for applications that need these characteristics. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Electrochemical attenuated total reflection surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) plays an important role in deciphering interfacial reaction mechanisms at molecular level. However, the corrosive etching of Si internal reflection element by OH− largely impedes reliable SEIRAS measurements in strong alkaline electrolytes. Herein, a dense and chemically inert nanocrystalline diamond (NCD) film is successfully fabricated at a thickness of ~120 nm through hot filament chemical vapor deposition on a micromachined Si wafer to insulate the OH− etching. A reversible interfacial water feature without spectral interference of Si‐O band is obtained in 1.0 mol·L–1 KOH on Au/NCD/Si film electrode. Afterwards, electrochemical CO reduction reaction on Cu film electrode is explored in different KOH concentrations ranging from 0.1 to 3.0 mol·L–1 as a model reaction. A redshift of COL band, as well as its lower intensity but faster depletion kinetics, is noted with increasing electrolyte pH, whereas COB is identified as an inert spectator accumulating on Cu surface. Our present work demonstrates the alkaline resistant feature of diamond/Si composite internal reflection element, which could be a powerful platform to study electrocatalytic reactions in strong alkaline media. [ABSTRACT FROM AUTHOR]

AbstractObjective: The aim of this study was to research the infrared spectroscopic features of various industrial hemp samples, establish a rapid infrared detection method for industrial hemp based on cannabidiol (CBD) content, and utilize infrared spectroscopy to differentiate industrial hemp flowers and leaves from different varieties and origins. Methods: Appropriate preprocessing was conducted on the industrial hemp samples based on their inherent characteristics. The samples were then scanned using the FTIR spectrometer, with careful subtraction of the background spectrum. A semi-quantitative rapid detection method for flowers and leaves using infrared spectroscopy was developed through partial least squares discriminant analysis. Data processing software was used to conduct principal component analysis and cluster analysis on the transmittance values of infrared characteristic absorption peaks, aiding in the identification and differentiation of samples from different varieties, origins, and harvest dates. Results: A semi-quantitative rapid detection method for industrial hemp flowers and leaves based on CBD content was successfully developed. Principal component analysis was able to clearly distinguish industrial hemp of different varieties and origins, effectively clustering samples of the same variety. This underscores the significant impact of mid-infrared spectroscopy in the identification and analysis of industrial hemp, providing an innovative approach to quickly identifying different hemp varieties. [ABSTRACT FROM AUTHOR]