Sharp Raman Bands Research Articles

Infrared and infrared emission spectroscopy of the zinc carbonate mineral smithsonite

Infrared emission and infrared spectroscopy has been used to study a series of selected natural smithsonites from different origins. An intense broad infrared band at 1440 cm −1 is assigned to the ν 3 CO 3 2− antisymmetric stretching vibration. An additional band is resolved at 1335 cm −1. An intense sharp Raman band at 1092 cm −1 is assigned to the CO 3 2− symmetric stretching vibration. Infrared emission spectra show a broad antisymmetric band at 1442 cm −1 shifting to lower wavenumbers with thermal treatment. A band observed at 870 cm −1 with a band of lesser intensity at 842 cm −1 shifts to higher wavenumbers upon thermal treatment and is observed at 865 cm −1 at 400 °C and is assigned to the CO 3 2− ν 2 mode. No ν 2 bending modes are observed in the Raman spectra for smithsonite. The band at 746 cm −1 shifts to 743 cm −1 at 400 °C and is attributed to the CO 3 2− ν 4 in phase bending modes. Two infrared bands at 744 and around 729 cm −1 are assigned to the ν 4 in phase bending mode. Multiple bands may be attributed to the structural distortion ZnO 6 octahedron. This structural distortion is brought about by the substitution of Zn by some other cation. A number of bands at 2499, 2597, 2858, 2954 and 2991 cm −1 in both the IE and infrared spectra are attributed to combination bands.

Raman and infrared spectroscopy of the manganese arsenate mineral allactite

The mineral allactite [Mn7(AsO4)2(OH)8] is a basic manganese arsenate which is highly pleochroic. The use of the 633nm excitation line enables quality spectra of to be obtained irrespective of the crystal orientation. The mineral is characterised by a set of sharp bands in the 770–885cm−1 region. Intense and sharp Raman bands are observed at 883, 858, 834, 827, 808 and 779cm−1. Collecting the spectral data at 77K enabled better band separation with narrower bandwidths. The observation of multiple AsO4 stretching bands indicates the non-equivalence of the arsenate anions in the allactite structure. In comparison the infrared spectrum shows a broad spectral profile with a series of difficult to define overlapping bands. The low wavenumber region sets of bands which are assigned to the ν2 modes (361 and 359cm−1), the ν4 modes (471, 452 and 422cm−1), AsO stretching vibrations at 331 and 324cm−1, and bands at 289 and 271cm−1 which may be ascribed to MnO stretching modes. The observation of multiple bands shows the loss of symmetry of the AsO4 units and the non-equivalence of these units in the allactite structure. The study shows that highly pleochroic minerals can be studied by Raman spectroscopy.

Extended tunnelling states in the benzoic acid crystal: Infrared and Raman spectra of the OH and OD stretching modes

We compare Raman and infrared spectra of the nuOH/OD modes in benzoic acid crystal powders at 7 K. The extremely sharp Raman bands contrast to the broad infrared profiles and suggest adiabatic separation of hydrogen (deuterium) dynamics from the crystal lattice. There is no evidence of any proton-proton coupling term. The assignment scheme is consistent with a quasisymmetric double-minimum potential, largely temperature independent. Tunnel splitting is a major band shaping mechanism, in addition to anharmonic coupling with lattice modes. The proton/deuteron dynamics are rationalized with nonlocal pseudoparticles and extended states. We propose a symmetry-related damping mechanism to account for the broad infrared profiles, as opposed to the sharp Raman bands. We assign spectral features to distinct interconversion mechanisms based on either pseudoparticle transfer or adiabatic pairwise transfer. We establish close contacts with theoretical models based on first-principles calculations.

An infrared and Raman spectroscopic study of natural zinc phosphates

Zinc phosphates are important in the study of the phosphatisation of metals. Raman spectroscopy in combination with infrared spectroscopy has been used to characterise the zinc phosphate minerals. The minerals may be characterised by the patterns of the hydroxyl stretching vibrations in both the Raman and infrared spectra. Spencerite is characterised by a sharp Raman band at 3516 cm −1 and tarbuttite by a single band at 3446 cm −1. The patterns of the Raman spectra of the hydroxyl stretching region of hopeite and parahopeite are different in line with their differing crystal structures. The Raman spectrum of the PO 4 stretching region shows better band separated peaks than the infrared spectra which consist of a complex set of overlapping bands. The position of the PO 4 symmetric stretching mode can be used to identify the zinc phosphate mineral. It is apparent that Raman spectroscopy lends itself to the fundamental study of the evolution of zinc phosphate films.

Raman spectroscopy and microwave properties of CaTiO3-based ceramics

x CaTiO 3 −(1−x) Sr ( Mg 1/3 Nb 2/3 ) O 3 (CTSMN) and yCaTiO3−(1−y)NdAlO3 (CTNA) microwave ceramics have been studied by x-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. TEM and XRD revealed that all compositions underwent octahedral tilt transitions on cooling, generally resulting in an a−a−c+ tilt system. The exception was the NdAlO3 end member, which had the R3̄c space group, consistent with an a−a−a− tilt configuration. Sr(Mg1/3Nb2/3)O3 (SMN), (x=0) also exhibited +/−1/3{hkl} reflections in x-ray and electron diffraction patterns associated with 1:2 long-range ordering of the B-site cations. For x⩾0.2, no 1:2 ordered reflections were observed. The long-range B-site ordering in SMN gave rise to sharp Raman bands at 391 and 825 cm−1. The 391 cm−1 band disappeared for x⩾0.2 and the width of the 825 cm−1 band became broader as x increased. It was concluded that for samples with x⩾0.2, only short-range ordering remained which decreased in correlation length as x increased. In CTNA solid solutions, a broad Raman band occurred at ∼800 cm−1 (absent for y=0 and 1 and strongest for y=0.5). The position of this band suggested that its origin was similar in nature to the ∼825 cm−1 band observed in CTSMN and therefore related to local short-range cation ordering. A relation between the presence of strong local order and poor Q in zero-temperature coefficient of the resonant frequency CTSMN (x≈0.2) is postulated.

Raman spectroscopy of B-site order–disorder in CaTiO3-based microwave ceramics

Abstract x CaTiO 3 –(1− x ) Sr(Mg 1/3 Nb 2/3 )O 3 (CTSMN) and y CaTiO 3 –(1− y ) NdAlO 3 (CTNA) were studied by Raman spectroscopy. A sharp Raman band at 825 cm −1 was observed in SrMg 1/3 Nb 2/3 O 3 , consistent with 1:2 long-range ordering of cations on the B-site. The intensity of this band decreased and its width increased with increasing x implying that the degree of order was reduced. A broad Raman band around 800 cm −1 , absent in both pure CaTiO 3 and NdAlO 3 , was found in CTNA solid solutions with the strongest intensity at x =0.5. The position and intensity of this band suggested that its origin was similar in nature to that observed in CTSMN. The occurrence of a band at ∼800 cm −1 in CTNA suggested a non-random distribution of Ti 4+ and Al 3+ on the B cation sites.

Polarized Raman scattering study of terminal stretching modes inK0.30MoO3

Polarized Raman spectra of blue bronze ${\mathrm{K}}_{0.30}{\mathrm{MoO}}_{3}$ are reinvestigated focusing particularly on a frequency range from 900 to 1000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, where remarkably sharp Raman bands, ``spikes,'' appear. This Brief Report proves that previously reported results on the spikes of blue bronze include serious faults with respect to (1) the selection rule, (2) the number, and (3) the origin of the bands: (1) The spikes are Raman active both above and below the Peierls transition temperature ${(T}_{p}),$ in contrast to previous studies, where the spikes were Raman inactive above ${T}_{p}.$ (2) Four spikes are observed with $\mathbf{E}\ensuremath{\perp}\mathbf{b}$ polarization, while in all the previous studies, the number of the spikes was reported to be three. (3) The origin of the spikes should be attributed to terminal Mo-O stretching vibrations rather than to electronic transitions previously proposed. In addition, vibrational mode assignment of the spikes based on the terminal Mo-O stretching vibration model is successfully made. This suggests that an analysis of terminal stretching Mo-O vibrations with Raman spectroscopy can be a useful probe for blue bronze.

X-ray diffraction and spectroscopic studies of oleic acid–sodium oleate

The sodium oleate–oleic acid (1:1) complex (NaHOl 2) is characterized using X-ray diffraction, FT-IR photoacoustic spectroscopy, FT–Raman spectroscopy, and DSC. The special arrangement of hydrogen-bonded pairs of carboxylic acid and carboxylate groups into unique ‘head-group’ is supported by frequency shifts and partial or total disappearance of characteristic vibrations of carboxylic acid dimer and of carboxylate groups. The well-ordered state of hydrocarbon chains is demonstrated by the existence of sharp Raman bands in the CC stretching region (1000–1150 cm −1) and other conformationally sensitive modes. The FT–Raman results suggest that the transition at about 32°C involves the cooperative melting of methyl- and carboxyl/carboxylate-sided hydrocarbon chains. From the X-ray diffraction data it is clear that this transition is associated with the disintegration of the hydrogen-bonded carboxylate–carboxylic acid complex, followed by the separate formation of oleic acid and sodium oleate. The packing of hydrocarbon chain in the acid–soap complex is different from the parent oleic acid or sodium oleate. The hydrocarbon chains in the NaHOl 2 form more stable packing (O ‖ subcell) in comparison to that of oleic acid. A temperature composition phase diagram is presented.

Hexacarbonyldiplatinum(I). Synthesis, Spectroscopy, and Density Functional Calculation of the First Homoleptic, Dinuclear Platinum(I) Carbonyl Cation, [{Pt(CO)3}2]2+, Formed in Concentrated Sulfuric Acid

The dissolution of PtO2 in concentrated H2SO4 under an atmosphere of CO results in the formation of hexacarbonyldiplatinum(I), [{Pt(CO)3}2]2+ (1), the first homoleptic, dinuclear, cationic platinum carbonyl complex, of which a prolonged evacuation leads to reversible disproportionation to give cis-[Pt(CO)2]2+(solv) (2) and Pt(0). 1 has been completely characterized by NMR (13C and 195Pt), IR, Raman, and EXAFS spectroscopy. The structure of 1 is rigid on the NMR time scale at room temperature. NMR: δ(13CA) 166.3, δ(13CB) 158.7, δ(195Pt) −211.0 ppm; 1J(Pt−CA) = 1281.5 Hz, 1J(Pt−CB) = 1595.7 Hz, 1J(Pt−Pt‘) = 550.9 Hz. The strongly polarized, sharp Raman band at 165 cm-1 (ρ = ca. 0.25) indicates the presence of a direct Pt−Pt bond. The IR and Raman spectra in the CO stretching region are entirely consistent with the presence of only terminal CO's on a nonbridged Pt−Pt bond with D2d symmetry. ν(CO)IR: 2174 (E), 2187 (B2), and 2218 cm-1 (B2); ν(CO)Raman: 2173 (E), 2194 (B2), 2219 (B2), 2209 (A1) and 2233 cm-...

Pseudo-lattice vibrations in smectic phase of liquid crystals: studies on small wave number Raman spectra of 4-alkyl-4′-cyanobiphenyl

Small wave number Raman spectra of 4-C n H 2 n +1-4′-cyanobiphenyl ( nCB) were measured for n=8,9,10,12. Sharp Raman bands are observed in common below about 10 cm −1 for the smectic A phase of these compounds. These bands are assigned to intermolecular vibrations along the direction perpendicular to the smectic layers each of which comprises two sublayers. Existence of such definite intermolecular vibrations has been reported previously by the present authors. We called them pseudo-lattice vibrations in smectic liquid crystals. Apparent force constant and damping factor of these vibrations are smaller for a larger n. These facts imply that for a larger n, the structural ordering in a sublayer is better, but the interaction between sublayers is smaller.

Surface-enhanced Raman assays (SERA): measurement of bilirubin and salicylate

Results of a study to detect bilirubin and salicylate using SERS and a reactive coating are presented. The motivation for this work was to devel to develop an assay that would simplify an analysis by detecting the analyte in a whole blood sample. This would remove the risks and time associated with preparing a serum sample. Quantitative analysis was performed using partial least-squares. The results are that one can detect bilirubin and salicylate in whole blood at levels below the normal or therapeutic levels using a coating based on an argentiphilic diazonium molecule. The sharp Raman bands associated with the analyte–coating adduct are sufficiently resolved to allow the analyte to be detected in the presence of a complex matrix such as whole blood. Copyright © 1999 John Wiley & Sons, Ltd.

The parathiocyanogen electrode

Stable, yellow anodic films of parathiocyanogen (SCN) x were formed on a platinum electrode from 2.8 M KSCN in methanol at 45 °C at a constant current of 20–40 mA cm−2 for 15–30 min. Loosely bound orange crystals of a more amorphous character were removed by rinsing to leave an adherent yellow film with sharp Raman bands under 647.1 nm laser excitation at 627 cm−1 (vCS), 1152 cm−1 and 1236–1261 cm−1 (vNN and vCN). The lack of electroactivity and short-lived photocurrents pointed to an insulating film at potentials up to 1.0 V (SHE). At more positive potentials, longer-lasting photocurrents were obtained, consistent with breakdown of the insulating film. XPS scans confirmed N:C:S ratios close to 1:1:1, with a deficiency of S of some 10% due to S lost as sulfate at the film surface. Oxidation of SeCN− in neutral aqueous solution led to the formation of a less-stable orange paraselenocyanogen film with a Raman band at 1256–1267 cm−1, which decomposed within a day to grey selenium.

Multiple-overtone resonance Raman scattering and fluorescence from I2 species adsorbed on silver surfaces

A detailed excitation profile of a Raman progression consisting of up to six overtones and a fundamental band at 123 cm−1 observed from iodide adsorbed on an electrochemically roughened silver surface at 20 K is analyzed. The excitation profile was constructed from 77 spectra obtained by tuning the laser wavelength in ∼0.25 nm steps through the spectral range 409 nm–433 nm. The shift between resonances in the excitation profile, corresponding to the spacing between vibronic levels in the excited state, is also equal to 123 cm−1 indicating that the ground state and excited state potential energy surfaces have the same shape. Only two distinct resonances spaced three vibrational quanta apart were evident in the profile for each band in the progression. Curve fitting of the Raman band shapes indicates that each overtone is composed of one sharp and one broad band, whereas the fundamental contains only one sharp component. The measured width of the fundamental was less than 2.5 cm−1 FWHM, limited by the instrument function. It is proposed that the sharp Raman bands represent a normal vibrational mode of a surface-adsorbed I2-like species with the width determined by the intrinsic vibrational dephasing in the ground state. On the other hand, the broad Raman bands reflect vibronic coupling between different I2-like species adsorbed on the same Ag cluster. The broad bandwidths result from both dephasing associated with the vibronic coupling and the intrinsic vibrational dephasing. Other weak emission bands are attributed to resonance fluorescence corresponding to direct transitions from higher vibronic levels of the excited state to the ground state. An emission at 429.9 nm is assigned to exciton recombination in small silver iodide clusters which are formed after spontaneous oxidation of the iodide-modified silver surface.

Quantitative Analysis of Sulfated Calcium Carbonates Using Raman Spectroscopy and X-ray Powder Diffraction

C. G. Kontoyannis, M. G. Orkoula and P. G. Koutsoukos, Analyst, 1997, 122, 33 DOI: 10.1039/A606167B

Attempted hydrothermal synthesis of diamond by hydrolysis of β-SiC powder

Hydrolysis of β-SiC powder in the “hydrothermal” pressure-temperature regime (1.4 kbar at 800 °C) leads to a sharp Raman band at 1330 cm −1. This suggests evidence for growth of diamonds under hydrothermal conditions. However, X-ray diffraction studies and scanning electron microscopy analysis do not provide the usual evidence for diamonds. Instead, they reveal euhedral monodisperse quartz crystals and a second acicular phase. It is possible that any diamond crystals are very small, with sizes of the order of few nanometers. However, transmission electron microscopy analysis reveals that the whiskers are a silicon oxycarbide with an approximate composition of SiO 1.6C 0.2 and have a width up to 100 nm and lattice imaging revealed 9.0 Å spacings.

Effect of Ion Exchange on Photoluminescence of Layered Niobates K4Nb6O17 and KNb3O8

Layered niobates K4Nb6O17 and KNb3O8 showed bright blue emission at 77 K. The luminescent properties were changed by exchanging potassium ions at interlayers with other cations. The luminescent intensity of NH4+-exchanged K4Nb6O17 was higher than that of native K4Nb6O17. In contrast, for H+-exchanged K4Nb6O17 and KNb3O8, the luminescent intensities decreased and the emission spectra red-shifted compared with their native layered niobates. The sharp and strong Raman bands (880 cm-1 for K4Nb6O17 and 955 cm-1 for KNb3O8) assigned to short Nb−O bonds which stuck out into interlayers were observed for the native layered niobates. The Raman bands were decreased by H+ exchange corresponding to the luminescent intensity. These results indicated that characteristics of the short Nb−O bonds were changed by cation exchange at interlayers, resulting in the change in the energy state of niobate layers. Thus, it was demonstrated that photophysical properties of niobate layers could be controlled by substances at interl...

Raman scattering in PbI 2 clusters incorporated into zeolite cages

Raman spectra of PbI 2 clusters in zeolite FAU and LTA are reported. A new Raman band with low frequency in the acoustic phonon region was observed in the cluster. The Raman shift was found to increase in inverse proportion to the radius of the cluster. In the optical phonon region, broad and weak Raman signals were observed, in contrast to the sharp and strong Raman bands in the bulk. The experimental results showed that the electron-acoustic phonon coupling via deformation potential interaction was the main process of the electron-phonon interaction due to the localization of the vibrational motion and the wavefunctions of the carriers in a small cluster, while Frohlich coupling to optical phonons became unimportant because of the neutralization of the electronic charge density. The quantized vibrational eigenmodes were calculated for the cluster. The calculated lowest spherical mode was in good agreement with the observed low-frequency Raman shift.

Vibrational spectra and structure of AsPS glasses

A structural model for AsPS glasses is proposed from an analysis of Raman and infrared spectra of two series of glasses with compositions (As 2S 3) 1 − x (P 2S 5) x with x = 0 – 0.7 and As x P x S 1−2 x with x = 0.10-0.16. The structural network in these glasses is composed of AsS 3 2 and S=PS 3 2 structural units forming 8-membered rings of As 2P 2S 4. The Raman spectra of these glasses are characterized by a sharp strong Raman band of 418 cm −1 ascribed to the breathing vibration of the rings. In the S-rich compositional region lying under the As 2S 3P 2S 5 line, towards the S corner of the AsPS phase diagram, sulfur atoms form S 8 molecules inside the structural network. In the 31P MAS-NMR spectrum by a single line with the chemical shift δ( 31 P) = 113.4 ppm is due to the S= PS 3 2 coordination of the phosphorus atom.

Raman microprobe analysis of Tl-Ca-Ba-Cu-O polycrystals

The spatial distribution of phases along the c axis of Tl-Ca-Ba-Cu-O syntactic polycrystals has been determined with ∼ 1 μm resolution using a Raman microprobe. In a crystal that is predominantly Tl 2CaBa 2Cu 2O 8 (Tl-2122), an intergrowth of ∼ 10 μm of TlCaBa 2CuBa 2O 7 (Tl-1122) is found in the crystal. In a crystal that is predominantly Tl 2Ca 2Ba 2Cu 3O 10 (Tl-2223), a layer ∼ 3 μm thick of Tl-2122 is found at one side of the crystal. Sharp Raman bands are observed at 108, 130, 407, 494, and 599 cm −1 for Tl-2122; at 92, 129, 498, and 599 cm −1 for Tl-2223; at 120, 146, and 528 cm −1 for Tl-1122. In addition, weak, broad bands are observed at ∼ 275 and ∼ 405 cm −1 for Tl-2223.

Investigaton of phase separation by Raman spectroscopy

Raman spectra of silica and borate glasses characteristically consist of a few rather broad bands, the frequencies of which are related to the network-forming units - silica tetrahedra, boron triangles, boron tetrahedra, etc. - and the extent to which these units are polymerized. Heat treatment that produces crystallization develops new sharp Raman bands which increase in intensity with time of heat treatment and which measure the evolution of the crystalline phases. Raman spectra of heat-treated glasses for which heat treatment produces glass-glass phase separation are in most cases identical to the original glass. Examination of the Raman spectra of phase-separated alkali borate and alkali silicate glasses leads to the conclusion that the melts from which these glasses are prepared are already clustered on an atomic scale so that they contain all of the network-forming linkages that will be segregated into thermodynamically distinct phases after heat treatment. The minimum size of the clusters is difficult to estimate but deductions from the spectra of germano-silicate glasses suggest it must be on the order of 5–10 tetrahedra.