Showing papers on "Infrared spectroscopy published in 2014"
TL;DR: Through rational variation in the surface moieties it is demonstrated that the photoluminescence of Si-NCs can be effectively tuned across the entire visible spectral region without changing particle size.
Abstract: The syntheses of colloidal silicon nanocrystals (Si-NCs) with dimensions in the 3–4 nm size regime as well as effective methodologies for their functionalization with alkyl, amine, phosphine, and acetal functional groups are reported. Through rational variation in the surface moieties we demonstrate that the photoluminescence of Si-NCs can be effectively tuned across the entire visible spectral region without changing particle size. The surface-state dependent emission exhibited short-lived excited-states and higher relative photoluminescence quantum yields compared to Si-NCs of equivalent size exhibiting emission originating from the band gap transition. The Si-NCs were exhaustively characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformed infrared spectroscopy (FTIR), and their optical properties were thoroughly investigated using fluorescence spectroscopy, excited-state lifetime measurements, photobleaching experiments, and solvatochromi...
275 citations
TL;DR: In this article, a biochar/MnOx composite, as a potential adsorbent, was successfully synthesized via KMnO4 modification of corn straw biochar (BC) under high temperature (600°C).
263 citations
TL;DR: In this paper, the photocatalytic performance of Ti3+ self-doped TiO2 was investigated using a simple one-step calcination method, by using low-cost NaBH4 as the reductant.
Abstract: Ti3+ self-doped TiO2 are successfully prepared via a simple one-step calcination method, by using low-cost NaBH4 as the reductant. The as-prepared samples are characterized by different techniques such as X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and Fourier transformation infrared spectroscopy (FTIR). EPR spectra confirm the presence of Ti3+ in the bulk of the samples rather than on the surface, which is the reason for the high photocatalytic performance of the catalyst under visible light irradiation. It is worth noting that the visible light absorption is enhanced after HCl washing, and the photocatalytic activity of Ti3+ self-doped TiO2 is proportional to the concentration of the doped Ti3+. Interestingly, the photocatalytic activity of the catalyst under UV light also increases after HCl washing treatment, which is caused by the increase of BET surface area.
238 citations
TL;DR: In this paper, a new insight into the structure of the early products of aniline oxidation based on their Raman spectra is reported, and the influence of smooth gold support on the Raman spectrum of the films has also been studied.
231 citations
TL;DR: In this review, an overview is provided of the main contributions that have been derived from IR absorption spectroscopy studies of catalytic systems, and a discussion is included on new trends and new potential directions of research involving IR in catalysis.
Abstract: Infrared absorption spectroscopy has proven to be one of the most powerful spectroscopic techniques available for the characterization of catalytic systems. Although the history of IR absorption spectroscopy in catalysis is long, the technique continues to provide key fundamental information about a variety of catalysts and catalytic reactions, and to also offer novel options for the acquisition of new information on both reaction mechanisms and the nature of the solids used as catalysts. In this review, an overview is provided of the main contributions that have been derived from IR absorption spectroscopy studies of catalytic systems, and a discussion is included on new trends and new potential directions of research involving IR in catalysis. We start by briefly describing the power of Fourier-transform IR (FTIR) instruments and the main experimental IR setups available, namely, transmission (TIR), diffuse reflectance (DRIFTS), attenuated total reflection (ATR-IR), and reflection–absorption (RAIRS), for advancing research in catalysis. We then discuss the different environments under which IR characterization of catalysts is carried out, including in situ and operando studies of typical catalytic processes in gas-phase, research with model catalysts in ultrahigh vacuum (UHV) and so-called high-pressure cell instruments, and work involving liquid/solid interfaces. A presentation of the type of information extracted from IR data follows in terms of the identification of adsorbed intermediates, the characterization of the surfaces of the catalysts themselves, the quantitation of IR intensities to extract surface coverages, and the use of probe molecules to identify and titrate specific catalytic sites. Finally, the different options for carrying out kinetic studies with temporal resolution such as rapid-scan FTIR, step-scan FTIR, and the use of tunable lasers or synchrotron sources, and to obtain spatially resolved spectra, by sample rastering or by 2D imaging, are introduced.
225 citations
TL;DR: The most common structural motifs of amyloid fibers are reviewed and how infrared spectroscopy and isotope labeling can be used to identify their structures and aggregation kinetics are discussed.
Abstract: There is an enormous amount of interest in the structures and formation mechanisms of amyloid fibers. In this Perspective, we review the most common structural motifs of amyloid fibers and discuss how infrared spectroscopy and isotope labeling can be used to identify their structures and aggregation kinetics. We present three specific strategies, site-specific labeling to obtain residue-by-residue structural information, isotope dilution of uniformly labeled proteins for identifying structural folds and protein mixtures, and expressed protein ligation for studying the domain structures of large proteins. For each of these methods, vibrational couplings are the source of the identifying features in the infrared spectrum. Examples are provided using the proteins hIAPP, Aβ, polyglutamine, and γD-crystallin. We focus on FTIR spectroscopy but also describe new observables made possible by 2D IR spectroscopy.
199 citations
TL;DR: In this paper, the anions and the protons of the cations in the halide ionic liquids have specific hydrogen-bond type of interaction, while the BF4− anion does not participate in the specific interaction, but interacts less specifically by positioning itself more above the ring plane of the imidazolium cation.
Abstract: Imidazolium-based ionic liquids having different anions 1-butyl-3-methylimidazolium ([BMIM]X: X = Cl−, Br−, I−, and BF4−) and their aqueous mixtures were investigated by IR absorption and proton NMR spectroscopy. The IR spectra of these ionic liquids in the CHx stretching region differed substantially, especially for C–H bonds in the imidazolium ring, and the NMR chemical shifts of protons in the imidazolium ring also varied markedly for ILs having different anions. Upon the introduction of water to screen the electrostatic forces and separate the ions, both IR and NMR spectra of [BMIM]X (X = Cl−, Br−, I−) showed significant changes, while those of [BMIM]BF4 did not change appreciably. H–D isotopic exchange rates of C(2)–H in [BMIM]X–D2O mixtures exhibited an order: C(2)–H⋯Cl > C(2)–H⋯Br > C(2)–H⋯I, while the C(2)–H of [BMIM]BF4 was not deuterated at all. These experimental findings, supported by DFT calculations, lead to the microscopic bulk configurations in which the anions and the protons of the cations in the halide ionic liquids have specific, hydrogen-bond type of interaction, while the BF4− anion does not participate in the specific interaction, but interacts less specifically by positioning itself more above the ring plane of the imidazolium cation. This structural change dictated by the anion type will work as a key element to build the structure–property relationship of ionic liquids.
194 citations
TL;DR: The comparison of experimental data and finite-difference time-domain simulations reveals a nonperfect filling of the gaps with sizes below 10 nm, which means that morphological information on the nanoscale is obtained additionally to chemical information.
Abstract: We report on the near-field coupling of individual gold nanoantennas arranged in tip-to-tip dimer configuration, leading to strong electromagnetic field enhancements in the infrared, which is of great interest for sensing applications such as surface-enhanced infrared spectroscopy. We quantitatively evaluated the enhancement of vibrational excitations of a 5 nm thick test layer of 4,4′-bis(N-carbazolyl)-1,1′-biphenyl as a function of different gap sizes. The dimers with the smallest gaps under investigation (∼3 nm) lead to more than 1 order of magnitude higher signal enhancement with respect to gaps of 50 nm width. The comparison of experimental data and finite-difference time-domain simulations reveals a nonperfect filling of the gaps with sizes below 10 nm, which means that morphological information on the nanoscale is obtained additionally to chemical information.
192 citations
TL;DR: The reversible CO binding suggests that these frameworks may be of utility for the separation of CO from various industrial gas mixtures, including CO/H2 and CO/N2, and selectivities determined from gas adsorption isotherm data using ideal adsorbed solution theory (IAST) indicate that all six M2(dobdc) frameworks could potentially be used as solid adsorbents to replace current cryogenic distillation technologies.
Abstract: Six metal–organic frameworks of the M2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobdc4– = 2,5-dioxido-1,4-benzenedicarboxylate) structure type are demonstrated to bind carbon monoxide reversibly and at high capacity. Infrared spectra indicate that, upon coordination of CO to the divalent metal cations lining the pores within these frameworks, the C–O stretching frequency is blue-shifted, consistent with nonclassical metal-CO interactions. Structure determinations reveal M–CO distances ranging from 2.09(2) A for M = Ni to 2.49(1) A for M = Zn and M–C–O angles ranging from 161.2(7)° for M = Mg to 176.9(6)° for M = Fe. Electronic structure calculations employing density functional theory (DFT) resulted in good agreement with the trends apparent in the infrared spectra and crystal structures. These results represent the first crystallographically characterized magnesium and zinc carbonyl compounds and the first high-spin manganese(II), iron(II), cobalt(II), and nickel(II) carbonyl species. Adsorption isotherms ind...
190 citations
TL;DR: Vibrational spectroscopy techniques provide a powerful approach to the study of environmental materials and processes as discussed by the authors, which can be used to probe molecular vibrations of solid, liquid, and gaseous samples for characterizing materials, elucidating reaction mechanisms, and examining kinetic processes.
Abstract: Vibrational spectroscopy techniques provide a powerful approach to the study of environmental materials and processes. These multifunctional analytical tools can be used to probe molecular vibrations of solid, liquid, and gaseous samples for characterizing materials, elucidating reaction mechanisms, and examining kinetic processes. Although Fourier transform infrared (FTIR) spectroscopy is the most prominent type of vibrational spectroscopy used in the field of soil science, applications of Raman spectroscopy to study environmental samples continue to increase. The ability of FTIR and Raman spectroscopies to provide complementary information for organic and inorganic materials makes them ideal approaches for soil science research. In addition, the ability to conduct in situ, real time, vibrational spectroscopy experiments to probe biogeochemical processes at mineral interfaces offers unique and versatile methodologies for revealing a myriad of soil chemical phenomena. This review provides a comprehensive overview of vibrational spectroscopy techniques and highlights many of the applications of their use in soil chemistry research.
TL;DR: In this paper, a new water soluble binder for Si anode of Li-ion batteries was investigated. But the binder was not shown to have a high first discharge capacity with a first coulombic efficiency of 89%.
TL;DR: One pot reduction and functionalization of graphene oxide (GO) with L-cysteine (L-cys-rGO) at the edges and basal planes of the carbon layers are presented in this article.
Abstract: One pot reduction and functionalization of graphene oxide (GO) with L-cysteine (L-cys-rGO) at the edges and basal planes of the carbon layers are presented. The L-cys-rGO was characterized by X-ray diffraction studies (XRD), X-ray photoelectron spectroscopy (XPS), attenuated infrared spectroscopy (ATIR), and Raman spectroscopy. The surface morphology was studied by scanning electron microscopy (SEM) and transmittance electron microscopy (TEM). The L-cys-rGO was further utilized for the simultaneous electrochemical quantification of environmentally harmful metal ions such as, Cd2+, Pb2+, Cu2+ and Hg2+. Detection limits obtained for these metal ions were 0.366, 0.416, 0.261 and 1.113 μg L−1 respectively. The linear range obtained for Cd2+, Cu2+ and Hg2+ was 0.4 to 2.0 μM and for Pb2+ was 0.4 to 1.2 μM. The detection limits were found to be less than the World Health Organization (WHO) limits. The developed protocol was applied for the determination of the above metal ions in various environmental samples and the results obtained were validated by atomic absorption spectroscopy (AAS).
TL;DR: In this article, a model of near-field spectroscopy derived from basic principles and verified by finite-element simulations is presented, demonstrating superb predictive agreement both with tunable quantum cascade laser near field spectroglobalization of SiO2 thin films and with newly presented nanoscale Fourier transform infrared (nanoFTIR) spectrogram of crystalline SiC.
Abstract: Near-field infrared spectroscopy by elastic scattering of light from a probe tip resolves optical contrasts in materials at dramatically subwavelength scales across a broad energy range, with the demonstrated capacity for chemical identification at the nanoscale. However, current models of probe-sample near-field interactions still cannot provide a sufficiently quantitatively interpretation of measured near-field contrasts, especially in the case of materials supporting strong surface phonons. We present a model of near-field spectroscopy derived from basic principles and verified by finite-element simulations, demonstrating superb predictive agreement both with tunable quantum cascade laser near-field spectroscopy of SiO2 thin films and with newly presented nanoscale Fourier transform infrared (nanoFTIR) spectroscopy of crystalline SiC. We discuss the role of probe geometry, field retardation, and surface mode dispersion in shaping the measured near-field response. This treatment enables a route to quantitatively determine nanoresolved optical constants, as we demonstrate by inverting newly presented nanoFTIR spectra of an SiO2 thin film into the frequency dependent dielectric function of its mid-infrared optical phonon. Our formalism further enables tip-enhanced spectroscopy as a potent diagnostic tool for quantitative nanoscale spectroscopy. © 2014 American Physical Society.
TL;DR: In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy in conjunction with H-D isotope replacement is used to investigate the dissociation and oxidation of CH3CH2OH on a Pd electrode in 01 M NaOH, with a focus on identifying the chemical nature of the pivotal intermediate in the so-called dual-pathway (C1 and C2) reaction mechanism as mentioned in this paper.
Abstract: In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy in conjunction with H–D isotope replacement is used to investigate the dissociation and oxidation of CH3CH2OH on a Pd electrode in 01 M NaOH, with a focus on identifying the chemical nature of the pivotal intermediate in the so-called dual-pathway (C1 and C2) reaction mechanism Real-time spectroelectrochemical measurements reveal a band at ∼1625 cm–1 showing up prior to the multiply bonded COad band CH3CD2OH and D2O are used to exclude the spectral interference with this band from interfacial acetaldehyde and H2O, respectively, confirming for the first time that the ∼1625 cm–1 band is due to the adsorbed acetyl on the Pd electrode in alkaline media The spectral results suggest that the as-adsorbed acetyl (CH3COad) is oxidized to acetate from approximately −04 V as the potential moves positively to conclude the C2 pathway Alternatively, in the C1 pathway, the CH3COad is decomposed to α-COad and β-CHx species on the
TL;DR: In this paper, the authors evaluated the interchangeability of the three FTIR techniques by analyzing 452 prehistoric and modern bioapatite samples and found that the attenuated total reflection (ATR) and diffuse reflectance infrared Fourier transform (DRIFT) produced more reliable results and were comparable to transmission FTIR.
TL;DR: In this paper, the application of infrared spectroscopy for identification and characterization of surface hydroxyl groups is reviewed, and the properties of OD and OH groups are compared, while the potential of other techniques is also briefly described.
Abstract: Surface hydroxyl groups are active centers in many catalytic reactions and can play an important role during catalyst preparation. In this chapter, the application of infrared spectroscopy for identification and characterization of surface OH groups is reviewed. The potential of other techniques is also briefly described. The vibrational signature of various types of hydroxyls is discussed; however, the amount of information that can be gathered from the hydroxyl spectra itself is limited. In contrast, application of probe molecules allows a profound characterization of hydroxyl species. Two scenarios are considered: the formation of H-bonds between hydroxyl groups and probe molecules, and chemical reactions between hydroxyl groups and molecules or ions (such as protonation of basic probe molecules, exchange reactions, redox processes). Means to explore the accessibility and location of hydroxyl groups are introduced. The properties of OD and OH groups are compared, and the application of H/D exchange as a diagnostic reaction is discussed. Finally, the hydroxyl population on materials of practical interest is analyzed.
TL;DR: In this paper, the complementary use of Raman and Fourier transform infrared (IR) spectroscopy for the detection of specific carbon chains and cations for the identification of metal carboxylates within oil paint microsamples.
Abstract: This work introduces the complementary use of μ-Raman and μ-Fourier transform infrared (IR) spectroscopy for the detection of specific carbon chains and cations for the identification of metal carboxylates within oil paint microsamples. Metal carboxylates (metal soaps) form naturally when free fatty acids react with metal cations and may also be found as additives or degradation products. Twenty-two metal carboxylates were synthesised, and their spectra assembled in a reference database. Metal salts of cations commonly present in oil paintings were used, including lead, zinc, calcium, cadmium, copper and manganese. The fatty acids selected were the saturated acids palmitic (C16 : 0) and stearic (C18 : 0) and the polyunsaturated oleic acid (C18 : 1). Azelaic acid (C9 diacid), a product resulting from autoxidation of polyunsaturated acids, was also included. Metal carboxylates were characterised by Raman and IR spectroscopy, and their structures were confirmed by X-ray diffraction. Raman and IR spectroscopy proved to be complementary techniques for a full identification of the metal carboxylates in complex aged paint. Raman enables the differentiation of the carbon chain length in the C–C stretching region (1120–1040 cm−1), and IR distinguishes the metal cation in the COO− stretching absorption region (1650–1380 cm−1). Principal component analysis was applied to the spectra in order to facilitate a fast and accurate method to discriminate between the different metal carboxylates and to aide in their identification. Finally, spectra from case studies were successfully projected in the principal component analysis models built, enabling a higher confidence level for the identification of copper palmitate and copper azelate in two 19th-century Portuguese oil paintings. Copyright © 2014 John Wiley & Sons, Ltd.
TL;DR: In this article, a novel BiOCl-g-C3N4 composite photocatalysts were synthesized by a one-step chemical bath method using X-ray diffraction (XRD), high-resolution transmission microscopy (HRTEM), UV-visible light diffusion reflectance spectrometry (DRS), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence spectrography (PL).
Abstract: Novel BiOCl–g-C3N4 composite photocatalysts were synthesized by a one-step chemical bath method. The composites were characterized using X-ray diffraction (XRD), high-resolution transmission microscopy (HRTEM), UV-visible light diffusion reflectance spectrometry (DRS), Fourier-transform infrared spectroscopy (FT-IR), and photoluminescence spectroscopy (PL). The results indicated that BiOCl was dispersed on g-C3N4 to form heterojunction structures with high specific surface areas. BiOCl–g-C3N4 showed higher photocatalytic activity than pure g-C3N4 and BiOCl for rhodamine B (RhB) degradation. The enhanced performance was induced by the high separation efficiency of photoinduced carriers. The active species trapping and quantification experiments indicated that the photoinduced charges transfer via a direct Z-scheme.
TL;DR: In this article, the authors found a direct relationship between the amount of recombination centers and photoactivity of the samples, which was evaluated by the decolorization of 25mg/L solution of Acid Orange 7 (AO-7).
TL;DR: In this paper, the authors have shown that ZnO acts as a network modifier with BiO6 octahedral structural units for glass samples with x = 5, 10, and 15.
TL;DR: In this paper, a topochemical oxidative reaction (TOR) under air is converted into a monometallic CoIICoIII-CO3 layered double hydroxide (LDH), and structural and morphological characterizations are performed using powder X-ray diffraction, Fourier-transformed IR spectroscopy, and scanning and transmission electron microscopy.
Abstract: Through a topochemical oxidative reaction (TOR) under air, a β-Co(OH)2 brucite type structure is converted into a monometallic CoIICoIII–CO3 layered double hydroxide (LDH). The structural and morphological characterizations are performed using powder X-ray diffraction, Fourier-transformed IR spectroscopy, and scanning and transmission electron microscopy. The local structure is scrutinized using an extended X-ray absorption fine structure, X-ray absorption near-edge structure, and pair distribution function analysis. The chemical composition of pristine material and its derivatives (electrochemically treated) are identified by thermogravimetry analysis for the bulk and X-ray photoelectron spectroscopy for the surface. The electrochemical behavior is investigated on deposited thin films in aqueous electrolyte (KOH) by cyclic voltammetry and electrochemical impedance spectroscopy, and their capacitive properties are further investigated by Galvanostatic cycling with potential limitation. The charge capacity is found to be as high as 1490 F g−1 for CoIICoIII–CO3 LDH at a current density of 0.5 A g−1. The performances of these materials are described using Ragone plots, which finally allow us to propose them as promising supercapacitor materials. A surface-to-bulk comparison using the above characterization techniques gives insight into the cyclability and reversibility limits of this material.
TL;DR: EDS result showed that the amount of Ni in the product is about 9%, these Ni doped hexagonal nanorods exhibits a blue shifts and weak (UV) emission peak, compared with pure ZnO, which may be induced by the Ni-doping different concentrations.
TL;DR: A detailed procedure for the quantitative analysis of aromatic and aliphatic hydrogen based on infrared spectroscopy was set up and implemented on some carbon-based materials produced from organic precursors (naphthalene pitch) and/or relevant in combustion field (asphaltenes, carbon particulate matter, carbon black), spanning in the H/C atomic ratio range from 0.1 to 1 as mentioned in this paper.
TL;DR: V vibrational spectroscopy was used to study how OH emerges from a so-called Criegee intermediate formed when ozone attacks 2-butene, suggesting that OH production is easier than current theory predicts.
Abstract: Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the troposphere, proceeds through energized Criegee intermediates that undergo unimolecular decay to produce OH radicals. Here, we used infrared (IR) activation of cold CH3CHOO Criegee intermediates to drive hydrogen transfer from the methyl group to the terminal oxygen, followed by dissociation to OH radicals. State-selective excitation of CH3CHOO in the CH stretch overtone region combined with sensitive OH detection revealed the IR spectrum of CH3CHOO, effective barrier height for the critical hydrogen transfer step, and rapid decay dynamics to OH products. Complementary theory provides insights on the IR overtone spectrum, as well as vibrational excitations, structural changes, and energy required to move from the minimum-energy configuration of CH3CHOO to the transition state for the hydrogen transfer reaction.
TL;DR: First results from a new 60 MHz 1H NMR bench-top spectrometer detected hazelnut oil adulteration of olive oil at 11.2%w/w and Bench-top 60 MHz NMR performs at least as well as FTIR for this type of application.
Abstract: We report the first results from a new 60 MHz 1H nuclear magnetic resonance (NMR) bench-top spectrometer, Pulsar, in a study simulating the adulteration of olive oil with hazelnut oil. There were qualitative differences between spectra from the two oil types. A single internal ratio of two isolated groups of peaks could detect hazelnut oil in olive oil at the level of ∼13%w/w, whereas a whole-spectrum chemometric approach brought the limit of detection down to 11.2%w/w for a set of independent test samples. The Pulsar’s performance was compared to that of Fourier transform infrared (FTIR) spectroscopy. The Pulsar delivered comparable sensitivity and improved specificity, making it a superior screening tool. We also mapped NMR onto FTIR spectra using a correlation-matrix approach. Interpretation of this heat-map combined with the established annotations of the NMR spectra suggested a hitherto undocumented feature in the IR spectrum at ∼1130 cm−1, attributable to a double-bond vibration.
TL;DR: In this article, the structural, magnetic, and electric properties of Co0.8Ni0.2CryFe2−yO4 (0.00≤y≤0.75; step 0.15) prepared via citrate precursor method are investigated.
TL;DR: The results indicate that the amount of aluminosilicate and its Si/Al ratio induce a shift in the T-O stretching band appearing at 950-1100 cm(-1), and FWHM of these bands indicates the participation of the crystalline phase relative to amorphous.
TL;DR: The potential of low-frequency Raman spectroscopy for the polymorphic characterization of APIs is demonstrated, which provides several benefits over existing techniques, including ease of sampling and more intense, information-rich band structures that can potentially discriminate among crystalline forms.
Abstract: Polymorph detection, identification, and quantitation in crystalline materials are of great importance to the pharmaceutical industry. Vibrational spectroscopic techniques used for this purpose include Fourier transform mid-infrared (FT-MIR) spectroscopy, Fourier transform near-infrared (FT-NIR) spectroscopy, Raman spectroscopy, and terahertz (THz) and far-infrared (FIR) spectroscopy. Typically, the fundamental molecular vibrations accessed using high-frequency Raman and MIR spectroscopy or the overtone and combination of bands in the NIR spectra are used to monitor the solid-state forms of active pharmaceutical ingredients (APIs). The local environmental sensitivity of the fundamental molecular vibrations provides an indirect probe of the long-range order in molecular crystals. However, low-frequency vibrational spectroscopy provides access to the lattice vibrations of molecular crystals and, hence, has the potential to more directly probe intermolecular interactions in the solid state. Recent advances in filter technology enable high-quality, low-frequency Raman spectra to be acquired using a single-stage spectrograph. This innovation enables the cost-effective collection of high-quality Raman spectra in the 200-10 cm(-1) region. In this study, we demonstrate the potential of low-frequency Raman spectroscopy for the polymorphic characterization of APIs. This approach provides several benefits over existing techniques, including ease of sampling and more intense, information-rich band structures that can potentially discriminate among crystalline forms. An improved understanding of the relationship between the crystalline structure and the low-frequency vibrational spectrum is needed for the more widespread use of the technique.