Raman microspectroscopic mapping or thermal system used to investigate milling‐induced solid‐state conversion of famotidine polymorphs

Confocal Raman microspectroscopy was used to nondestructively determine the polymorphic conversion of famotidine in the course of the milling process. A mapping system was applied to assess the blending uniformity of each polymorphic component in the milled mixture. Raman microspectroscopy combined with a thermal analyzer was also used to investigate the synergistic co‐effects of milling and heating on the polymorphic conversion of famotidine polymorphs. Famotidine has two polymorphs, forms A and B, the raw material of famotidine used was proved to be of form B. The Raman peak intensity ratio of the 2920 cm⁻¹ band for form A and 2897 cm⁻¹ band for form B was used to act as an indicator to evaluate the polymorphic conversion of famotidine form B to form A after different milling courses. The results indicate that the peak intensity at 2897 cm⁻¹ gradually decreased with the milling time, whereas the peak intensity at 2920 cm⁻¹ slowly enlarged, suggesting the polymorphic conversion of famotidine from form B to form A. The longer milling process might strongly induce and promote this polymorphic conversion of famotidine. Both polymorphic forms of famotidine were found to be well uniformly distributed within the milled samples due to their smaller varieties by using the Raman microscopic mapping system. The temperature effect could synergistically accelerate the polymorphic conversion of famotidine from form B to form A in the milled sample. The thermal‐dependent critical temperature for sharply enhancing the content of famotidine form A in each milled sample was also identified. Copyright © 2007 John Wiley & Sons, Ltd.     

Measurement of the absolute Raman scattering cross section of the 1584‐cm−1 band of benzenethiol and the surface‐enhanced Raman scattering cross section enhancement factor for femtosecond laser‐nanostructured substrates

The absolute Raman scattering cross section (σ_RS) for the 1584‐cm⁻¹ band of benzenethiol at 897 nm (1.383 eV) has been measured to be 8.9 ± 1.8 × 10⁻³⁰ cm² using a 785‐nm pump laser. A temperature‐controlled, small‐cavity blackbody source was used to calibrate the signal output of the Raman spectrometer. We also measured the absolute surface‐enhanced Raman scattering cross section (σ_SERS) of benzenethiol adsorbed onto a silver‐coated, femtosecond laser‐nanostructured substrate. Using the measured values of 8.9 ± 1.8 × 10⁻³⁰ and 6.6 ± 1.3 × 10⁻²⁴ cm² for σ_RS and σ_SERS respectively, we calculate an average cross‐section enhancement factor (EF) of 0.8 ± 0.3 × 10⁶. Copyright © 2009 John Wiley & Sons, Ltd.     

Measurement of the absolute Raman scattering cross sections of sulfur and the standoff Raman detection of a 6‐mm‐thick sulfur specimen at 1500 m

The absolute Raman scattering cross sections (σ_RS) for the 471, 217, and 153 cm⁻¹ modes of sulfur were measured as 6.0 ± 1.2 × 10⁻²⁷, 7.7 ± 1.6 × 10⁻²⁷, and 1.2 ± 0.24 × 10⁻²⁶ cm² at 815, 799, and 794 nm, respectively, using a 785‐nm pump laser. The corresponding values of σ_RS at 1120, 1089, and 1081 nm were determined to be 1.5 ± 0.3 × 10⁻²⁷, 1.2 ± 0.24 × 10⁻²⁷, and 1.2 ± 0.24 × 10⁻²⁷ cm² using a 1064‐nm laser. A temperature‐controlled, small‐cavity (2.125 mm diameter) blackbody source was used to calibrate the signal output of the Raman spectrometers for these measurements. Standoff Raman detection of a 6‐mm‐thick sulfur specimen located at 1500 m from the pump laser and the Raman spectrometer was made using a 1.4‐W, CW, 785‐nm pump laser. Copyright © 2010 John Wiley & Sons, Ltd.     

Complex impedance study of annealing effects on polycrystalline KDP conductivity

Annealing effects on the conductivity of KDP (KH₂PO₄) samples prepared either by melting under slight pressure (5.7 kgf/cm²) or by powder compression (1.3 × 10³kgf/cm²) were studied in air by complex impedance spectroscopy. In both cases, annealing at 423 K reduces the conductivities to constant values: from 6.2 × 10 ⁻⁶ to 1.6 × 10⁻⁷ Ω⁻¹ cm⁻¹ for samples prepared by melting and from 1.9 × 10^∼7 to 6.1 × 10^∼8 Ω⁻¹ cm⁻¹ for samples prepared by compression. Heating KDP at about 500 K significantly modifies its electric properties. Two relaxation processes are observed after this treatment. One of them is associated with a fairly strong dielectric polarizability. A small conductivity jump is observed close to 440 K.     

Raman study of datolite CaBSiO4(OH) at simultaneously high pressure and high temperature

Using an in situ method of Raman spectroscopy and resistance‐heated diamond anvil cell, the system datolite CaBSiO₄(OH) – water has been investigated at simultaneously high pressure and temperature (up to Р ~5 GPa and Т ~250 °С). Two polymorphic transitions have been observed: (1) pressure‐induced phase transition or the feature in pressure dependence of Raman band wavenumbers at P = 2 GPа and constant T = 22 °С and (2) heating‐induced phase transition at T ~90 °С and P ~5 GPа. The number of Raman bands is retained at the first transition but changed at the second transition. The first transition is mainly distinguished by the changes in the slopes of pressure dependence of Raman peaks at 2 GPa. The second transition is characterized by several strong changes: the wavenumber jumps of major bands, the merging of strong doublets at 378 and 391 cm⁻¹ (values for ambient conditions), the splitting of the intermediate‐intensity band at 292 cm⁻¹, and the transformation of some low‐wavenumber bands at 160–190 cm⁻¹. No spectral and visual signs of overhydration and amorphization have been observed. No noticeable dissolution of datolite in the water medium occurred at 5 GPa and 250 °С after 3 h, which corresponds to typical conditions of the ‘cold’ zones of slab subduction. Copyright © 2014 John Wiley & Sons, Ltd.     

Photodissociation effects on pulsed laser deposited silver oxide thin films: surface‐enhanced resonance Raman scattering

Temporal Raman scattering measurements with 488, 532 and 632 nm excitation wavelengths and normal Raman studies by varying the power (from 30 W/cm² to 2 MW/cm²) at 488 nm were performed on silver oxide thin films prepared by pulsed‐laser deposition. Initially, silver oxide Raman spectra were observed with all three excitation wavelengths. With further increase in time and power, silver oxide photodissociated into silver nanostructures. High‐intensity spectral lines were observed at 1336 ± 25 and 1596 ± 10 cm⁻¹ with 488 nm excitation. No spectral features were observed with 633 nm excitation. Surface‐enhanced resonance Raman scattering theory is used to explain the complex behavior in the intensity of the 1336/1596 cm⁻¹ lines with varying power of 488 nm excitation. Copyright © 2011 John Wiley & Sons, Ltd.     

分子间费米共振增强二元溶液体系的受激拉曼散射研究

研究了液芯光纤内不同体积比的甲苯和间二甲苯二元混合溶液的受激拉曼散射.实验结果表明:在不同的体积比之下二元溶液的环呼吸振动模式1002 cm^-1,甲基的CH伸缩振动模式2920 cm^-1 以及芳香环CH对称伸缩振动模式3058 cm^-1的拉曼带同时产生受激拉曼辐射,并且2920 cm^-1 和 3058 cm^-1 拉曼带的一阶受激拉曼散射阈值要低于1002 cm^-1拉曼带的二阶 关键词： 分子间费米共振 二元溶液 受激拉曼散射 拉曼散射截面     

Thermo‐Raman spectroscopy of synthetic nesquehonite — implication for the geosequestration of greenhouse gases

Pure nesquehonite (MgCO₃·3H₂O)/Mg(HCO₃)(OH)·2H₂O was synthesised and characterised by a combination of thermo‐Raman spectroscopy and thermogravimetry with evolved gas analysis. Thermo‐Raman spectroscopy shows an intense band at 1098 cm⁻¹, which shifts to 1105 cm⁻¹ at 450 °C, assigned to the ν₁CO₃²⁻ symmetric stretching mode. Two bands at 1419 and 1509 cm⁻¹ assigned to the ν₃ antisymmetric stretching mode shift to 1434 and 1504 cm⁻¹ at 175 °C. Two new peaks at 1385 and 1405 cm⁻¹ observed at temperatures higher than 175 °C are assigned to the antisymmetric stretching modes of the (HCO₃)⁻ units. Throughout all the thermo‐Raman spectra, a band at 3550 cm⁻¹ is attributed to the stretching vibration of OH units. Raman bands at 3124, 3295 and 3423 cm⁻¹ are assigned to water stretching vibrations. The intensity of these bands is lost by 175 °C. The Raman spectra were in harmony with the thermal analysis data. This research has defined the thermal stability of one of the hydrous carbonates, namely nesquehonite. Thermo‐Raman spectroscopy enables the thermal stability of the mineral nesquehonite to be defined, and, further, the changes in the formula of nesquehonite with temperature change can be defined. Indeed, Raman spectroscopy enables the formula of nesquehonite to be better defined as Mg(OH)(HCO₃)·2H₂O. Copyright © 2008 John Wiley & Sons, Ltd.     

高性能ZnO纳米块体材料的制备及其拉曼光谱学特征

利用六面顶高压设备制备了高密度、低脆性、纳米级的ZnO块体材料，用MDI/JADE5 X射线衍射仪(Cu靶)和XL30S-FEG场发射扫描电子显微镜对高压样品的相组成、晶粒尺寸及微观形貌进行了表征.利用E55+FRA106/5傅里叶变换激光拉曼光谱仪通过ZnO块体样品位于50—500cm^-1之内的拉曼光谱, 研究了极性半导体纳米材料的拉曼光谱学特征.发现在极性半导体ZnO纳米块体材料中，没有出现明显的尺寸限制效应. 关键词： ZnO纳米块体 拉曼光谱 尺寸限制效应     

Studies on the resonance Raman spectra of polyaniline obtained with near‐IR excitation

The effects of near‐IR (NIR) laser power over the Raman spectra of poly(aniline) emeraldine salt (PANI‐ES) and base (PANI‐EB) were investigated. The reasons for the existence of several bands from 1324 to 1500 cm⁻¹ in the Raman spectra of poly(aniline) obtained at NIR region were also studied. The bands from 1324 to 1375 cm⁻¹ were associated to νC N of polarons with different conjugation lengths and the bands from 1450 to 1500 cm⁻¹ in Raman spectra of PANI emeraldine and pernigraniline base forms were correlated to νCN modes associated with quinoid units having different conjugation lengths. The increase of laser power at 1064.0 nm causes the deprotonation of PANI‐ES and the formation of cross‐linking segments having phenazine and/or oxazine rings. For PANI‐EB only a small spectral change is observed when the laser power is increased, owing to the low absorption of this form in the NIR region. Copyright © 2007 John Wiley & Sons, Ltd.     

Layer‐dependent resonant Raman scattering of a few layer MoS2

We report resonant Raman scattering of MoS₂ layers comprising of single, bi, four and seven layers, showing a strong dependence on the layer thickness. Indirect band gap MoS₂ in bulk becomes a direct band gap semiconductor in the monolayer form. New Raman modes are seen in the spectra of single‐ and few‐layer MoS₂ samples which are absent in the bulk. The Raman mode at ~230 cm⁻¹ appears for two, four and seven layers. This mode has been attributed to the longitudinal acoustic phonon branch at the M point (LA(M)) of the Brillouin zone. The mode at ~179 cm⁻¹ shows asymmetric character for a few‐layer sample. The asymmetry is explained by the dispersion of the LA(M) branch along the Γ‐M direction. The most intense spectral region near 455 cm⁻¹ shows a layer‐dependent variation of peak positions and relative intensities. The high energy region between 510 and 645 cm⁻¹ is marked by the appearance of prominent new Raman bands, varying in intensity with layer numbers. Resonant Raman spectroscopy thus serves as a promising non invasive technique to accurately estimate the thickness of MoS₂ layers down to a few atoms thick. Copyright © 2012 John Wiley & Sons, Ltd.     

Transition of chromium oxyhydroxide nanomaterials to chromium oxide: a hot‐stage Raman spectroscopic study

The transition of disc‐like chromium hydroxide nanomaterials to chromium oxide nanomaterials has been studied by hot‐stage Raman spectroscopy. The structure and morphology of α‐CrO(OH) synthesised using hydrothermal treatment were confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The Raman spectrum of α‐CrO(OH) is characterised by two intense bands at 823 and 630 cm⁻¹ attributed to ν₁ Cr^III O symmetric stretching mode and the band at 1179 cm⁻¹ attributed to Cr^III OH δ deformation modes. No bands are observed above 3000 cm⁻¹. The absence of characteristic OH stretching vibrations may be due to short hydrogen bonds in the α‐CrO(OH) structure. Upon thermal treatment of α‐CrO(OH), new Raman bands are observed at 599, 542, 513, 396, 344 and 304 cm⁻¹, which are attributed to Cr₂O₃. This hot‐stage Raman study shows that the transition of α‐CrO(OH) to Cr₂O₃ occurs before 350 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of the structural order of all‐trans‐β‐carotene on the Raman scattering cross section at low concentrations

Using the technique of liquid‐core optical fiber (LCOF), we measured the Raman scattering cross sections (RSCSs) of the carbon–carbon (C C) stretching vibrational modes of all‐trans‐β‐carotene in carbon disulfide (CS₂) at concentrations ranging from 10⁻⁶ to 10⁻¹¹ M . It was found that the RSCSs of all‐trans‐β‐carotene were extremely high with decreasing concentration, and the absolute RSCS of C stretching modes of all‐trans‐β‐carotene reached the value of 2.6 × 10⁻²⁰ cm² molecule⁻¹ Sr⁻¹ at 8 × 10⁻¹¹ M , which is larger than at 8 × 10⁻⁶ Mby 4 orders of magnitude. A theoretical interpretation of the anomalous experimental results is given, which introduces a qualitative nonlinear model of coherent weakly damped electron‐lattice vibrations in structural order of all‐trans‐β‐carotene. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman fingerprint of the interaction of K+ with the COO− group of zwitterionic alanine

The interaction of K⁺ with the zwitterionic form of alanine (ZAla) is investigated using Raman spectroscopy and density functional theory calculations. The Raman spectra of an aqueous solution of Ala and its mixture with KOH at different molar concentrations [ZAla + xKOH, x = 1–5 M] have been recorded in the spectral region 400–1800 cm⁻¹. The wavenumber position of the band at ~529 cm⁻¹ shows a red shift of 14 cm⁻¹, while the Raman band at ~634 cm⁻¹ shows a blue shift of 10 cm⁻¹ with the increasing x from 1 to 5 M. The intensity ratio I₆₃₄/I₅₂₉ is increased with increasing x, and it could be because of the increase in concentration of the [ZAla + K⁺] complex in the solution. The new Raman band appeared at ~1079 cm⁻¹ in the Raman spectra of [ZAla + xKOH, x = 1–5] complex. To determine the most probable site for the interaction of K⁺ with ZAla, the structures of ZAla and the [ZAla + K⁺] were optimized at B3LYP/6‐311++G(d,p) level of theory. The electrostatic potential calculation carried out for ZAla reveals that the maximum density of electron is lying over COO⁻, and therefore, COO⁻ would be the most probable site for the interaction of K⁺ with ZAla. The theoretically calculated Raman spectra of ZAla, [ZAla + K⁺] and the [ZAla⁻ + K⁺] are in good agreement with experimentally observed Raman spectra. Thus, the Raman bands at ~529, 634, and 1079 cm⁻¹ may be used as the Raman fingerprint for the interaction of K⁺ with COO⁻ of the ZAla and ZAla⁻. Copyright © 2015 John Wiley & Sons, Ltd.     

Spectroscopic analysis of a dye–mineral composite–a Raman and FT‐IR study

In this investigation, we address the question of how organic thioindigo binds to inorganic palygorskite to form a pigment similar to Maya Blue. We also address how such binding, if it occurs, might be affected by varying the proportion of dye relative to that of the mineral, and by varying the length of heating time used in preparation of the pigment. In addition to samples of palygorskite and thioindigo both alone, four synthetic pigment samples were prepared; two samples of 8 wt.% dye, one heated at 170 °C for 3 h and one at 170 °C for 9 h, and two samples of 16 wt.% dye, one heated at 170 °C for 3 h and one at 170 °C for 9 h. All samples were examined using Fourier transform‐infrared (FT‐IR) and FT‐Raman spectroscopy. For the pigment samples, FT‐IR peaks at 1627 cm⁻¹ are attributed to a downshifted CO stretching mode of thioindigo due to dye–clay interaction. This interpretation is corroborated by FT‐Raman CO peaks with 14 cm⁻¹ shifts to lower wavenumber for the pigment relative to thioindigo alone. Additional Raman scattering between 550 cm⁻¹ and 650 cm⁻¹ also suggests dye–clay interaction through metal–oxygen bonding. We are thus led to the possibility of mostly hydrogen bonding between silanol and carbonyl at lower dye concentration, with a predominance of metal–oxygen bonding at higher dye concentration. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the hydrogen‐arsenate mineral pharmacolite Ca(AsO3OH)·2H2O—implications for aquifer and sediment remediation

The removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared (IR) spectroscopy have been used to study the mineral pharmacolite Ca(AsO₃OH)· 2H₂O. The mineral is characterised by an intense Raman band at 865 cm⁻¹ assigned to the ν₁ (AsO₃)²⁻ symmetric stretching mode. The equivalent IR band is found at 864 cm⁻¹. The low‐intensity Raman bands in the range from 844 to 886 cm⁻¹ provide evidence for ν₃ (AsO₃) antisymmetric stretching vibrations. A series of overlapping bands in the 300‐450 cm⁻¹ region are attributed to ν₂ and ν₄ (AsO₃) bending modes. Prominent Raman bands at around 3187 cm⁻¹ are assigned to the OH stretching vibrations of hydrogen‐bonded water molecules and the two sharp bands at 3425 and 3526 cm⁻¹ to the OH stretching vibrations of only weakly hydrogen‐bonded hydroxyls in (AsO₃OH)²⁻ units. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the antimonate mineral brandholzite Mg[Sb2(OH)12]·6H2O

Raman spectra of brandholzite Mg[Sb₂(OH)₁₂]·6H₂O were studied, complemented with infrared spectra, and related to the structure of the mineral. An intense Raman sharp band at 618 cm⁻¹ is attributed to the SbO symmetric stretching mode. The low‐intensity band at 730 cm⁻¹ is ascribed to the SbO antisymmetric stretching vibration. Low‐intensity Raman bands were found at 503, 526 and 578 cm⁻¹. Corresponding infrared bands were observed at 527, 600, 637, 693, 741 and 788 cm⁻¹. Four Raman bands observed at 1043, 1092, 1160 and 1189 cm⁻¹ and eight infrared bands at 963, 1027, 1055, 1075, 1108, 1128, 1156 and 1196 cm⁻¹ are assigned to δ SbOH deformation modes. A complex pattern resulting from the overlapping band of the water and hydroxyl units is observed. Raman bands are observed at 3240, 3383, 3466, 3483 and 3552 cm⁻¹; infrared bands at 3248, 3434 and 3565 cm⁻¹. The Raman bands at 3240 and 3383 cm⁻¹ and the infrared band at 3248 cm⁻¹ are assigned to water‐stretching vibrations. The two higher wavenumber Raman bands observed at 3466 and 3552 cm⁻¹ and two infrared bands at 3434 and 3565 cm⁻¹ are assigned to the stretching vibrations of the hydroxyl units. Observed Raman and infrared bands in the OH stretching region are associated with O‐H···O hydrogen bonds and their lengths 2.72, 2.79, 2.86, 2.88 and 3.0 Å (Raman) and 2.73, 2.83 and 3.07 Å (infrared). Copyright © 2009 John Wiley & Sons, Ltd.     

High‐resolution stimulated Raman spectroscopy and analysis of the 2ν10 overtone symmetric motion of C2H4

The high‐resolution stimulated Raman spectrum of the 2ν₁₀ band located at 1664.16 cm⁻¹ of C₂H₄ has been reanalyzed, thanks to the tensorial formalism developed in Dijon for X₂Y₄ asymmetric‐top molecules. A total of 191 lines were assigned and fitted as a single band without including perturbations such as Fermi or Coriolis coupling constants. We obtained a global root mean square deviation of 8.5 × 10⁻³ cm⁻¹. Further investigations are required to include interactions with the ν₂ and ν₇ + ν₁₀ bands. Copyright © 2009 John Wiley & Sons, Ltd.     

First order Raman scattering analysis of transition metal ions implanted GaN

Transition Metal (TM) ions V, Cr, Mn and Co were implanted into GaN/sapphire films at fluences 5×10¹⁴, 5×10¹⁵ and 5×10¹⁶ cm⁻². First order Raman Scattering (RS) measurements were carried out to study the effects of ion implantation on the microstructure of the materials, which revealed the appearance of disorder and new phonon modes in the lattice. The variations in characteristic modes 1GaN i.e. E₂(high) and A₁(LO), observed for different implanted samples is discussed in detail. The intensity of nitrogen vacancy related vibrational modes appearing at 363 and 665 cm⁻¹ was observed for samples having different fluences. A gallium vacancy related mode observed at 277/281 cm⁻¹ for TM ions implanted at 5×10¹⁴ cm⁻² disappeared for all samples implanted with rest of fluences. The fluence dependent production of implantation induced disorder and substitution of TM ions on cationic sites is discussed, which is expected to provide necessary information for the potential use of these materials as diluted magnetic semiconductors in future spintronic devices.     

In situ monitoring of solid‐state transition of p‐aminobenzoic acid polymorphs using Raman spectroscopy

The purpose of this study is to investigate the mechanism of solid‐state polymorphic transition of p‐aminobenzoic acid (PABA) using in situ Raman spectroscopy measurement. The polymorphic transition experiments were conducted on a micro quartz vessel mounted on a microscope, hot and cold stage, under isothermal conditions. The temperature was precisely controlled by a standalone temperature controller equipped with liquid nitrogen cooling system. The Raman spectroscopy probe was positioned on the surface of the solid sample in the micro vessel. The polymorphic transition progression was in situ monitored and recorded by Raman spectroscopy. Based on the polymorphic transition rate resulted from the quantitative analysis of Raman spectra, the mechanism of solid‐state polymorphic transition of PABA was examined by various empirical kinetic models. An Arrhenius analysis was also performed to calculate activation energies from 134.7 kJ mol⁻¹ to 137.7 kJ mol⁻¹ for the transition. The results demonstrated that in situ Raman spectroscopy is a valuable and accurate technique to probe polymorphic transition process. Copyright © 2009 John Wiley & Sons, Ltd.