Laser Raman Study Research Articles

Raman Spectroscopic Technique to Distinguish Constituents of Hydrocarbon-Bearing Fluid Inclusions of Kerala-Konkan Basin, Western offshore, India

Fluid inclusion studies have a great diversity of applications in exploration geology and are necessary tools in the determination of palaeotemperature and nature of fluids associated with the rocks in a basin. Using various fluid inclusion techniques such as petrography, microthermometry and Laser Raman Spectroscopy of fluid inclusions with Hydrocarbon fluid inclusions (HCFIs) help us to understand the generation potential of the basin. The representative micron sized fluid inclusions that intruded into the different geological formations of the KK-4C-A1well drilled by Oil and Natural Gas Corporation in Kerala-Konkan Basin, India has been selected for this study. Petrographic analyses confirm the presence of HCFIs with the help of Ultraviolet (UV) light. Raman spectra of HCFIs identified in different formations were examined. The temperature of homogenization (Th) obtained through microthermometric analysis of the fluid inclusions indicate the palaeotemperature of the sedimentary rock units. Coeval-aqueous inclusions associated to HCFIs show Th within the oil window range 60-140oC, indicating a temperature favourable for oil generation in Kerala-Konkan Basin (K-K Basin).Characterisation of hydrocarbon bearing fluid inclusions were carried out using Raman spectroscopy. HCFIs were observed in the annealed micro-cracks of Cannanore (Early Miocene), Calicut (Early Oligocene) formation (Type I) and Kasaragod (Palaeocene to Early Eocene) Formation (Type II), might get trapped along the micro-fracture by re-healing process. Laser Raman study could decipher hydrocarbon species such as Alkanes, SO2, COS, H2S, etc. Keywords: Hydrocarbon Fluid Inclusions, Oil Window Temperature, Raman Spectroscopy, Kerala-Konkan Basin

Effect of deposition temperature on key optoelectronic properties of electrodeposited cuprous oxide thin films

The cuprous oxide (Cu2O) thin films were electrodeposited with different reaction temperatures. The structural, morphological, optical, photoluminescence and photo response properties of the deposited films were analyzed. XRD analysis reveals cubic crystal structure for the deposited films with polycrystalline nature. The film deposited at room temperature possess high crystallite size of 37 nm. The surface morphology shows that by increasing the deposition temperature pyramid shaped morphology changes. Laser Raman study confirms the peaks 109, 148, 219, 415 and 635 cm−1 conforms the Cu2O phase formation. The band gap of the films are 2.02, 2.10 and 2.27 eV for the RT, 40 and 50 °C, respectively. The photoluminescence spectral analysis contains an emission peak at 618 nm confirm the formation of Cu2O. The photo response study confirms the ohmic nature of the films. The film electrodeposited at room temperature showed good I–V curve at the illumination of 300 W cm−2.

The Driving Forces of Guest Substitution in Gas Hydrates—A Laser Raman Study on CH4-CO2 Exchange in the Presence of Impurities

The recovery of CH4 gas from natural hydrate formations by injection of industrially emitted CO2 is considered to be a promising solution to simultaneously access an unconventional fossil fuel reserve and counteract atmospheric CO2 increase. CO2 obtained from industrial processes may contain traces of impurities such as SO2 or NOx and natural gas hydrates may contain higher hydrocarbons such as C2H6 and C3H8. These additions have an influence on the properties of the resulting hydrate phase and the conversion process of CH4-rich hydrates to CO2-rich hydrates. Here we show results of a microscopic and laser Raman in situ study investigating the effects of SO2-polluted CO2 and mixed CH4-C2H6 hydrate on the exchange process. Our study shows that the key driving force of the exchange processes is the establishment of the chemical equilibrium between hydrate phase and the surrounding phases. The exchange rate is also influenced by the guest-to-cavity ratio as well as the thermodynamic stability in terms of p-T conditions of the original and resulting hydrate phase. The most effective molecule exchange is related to structural changes (sI-sII) which indicates that hydrate decomposition and reformation processes are the occurring processes.

Mineralogy and geochemistry of four lunar soils by laser-Raman study

Laser Raman spectroscopy is used to investigate four lunar soils, focusing on mineralogy of grains of <45 μm size. Apollo samples 14163, 15271, 67511, and 71501 were selected as endmembers to study, based on their soil chemistry, maturity, and sample locations. Typical Raman spectral features for major and minor lunar minerals are discussed on the basis of major vibrational modes. We used the Raman peak shift to calculate Mg/(Mg + Fe + Ca) and Ca/(Mg + Fe + Ca) for pyroxene and Mg/(Mg + Fe) for olivine, and thus obtained the compositional distributions of these two minerals in each of the four lunar soils. Classification of feldspar grains was made based on recognition of their Raman patterns. A Raman point-counting procedure was applied to derive mineral modes of the soils, and these are found to be consistent with published modal analysis of these soils. The compositional distributions of pyroxene and olivine grains in each soil sample, as well as the mineral modes, reflect characteristics of the main source materials for these soils. Raman patterns and peak positions also reflect shock effects on plagioclase and quartz, found in 14163.

Microwave Dielectric Properties of Low‐Temperature Sinterable BaCe2(MoO4)4 Ceramics

Low‐temperature sinterable BaCe2(MoO4)4 ceramics were prepared through solid‐state ceramic route. X‐ray diffraction, laser Raman spectroscopy and scanning electron microscopy techniques have been used to investigate the structure and microstructure of BaCe2(MoO4)4 ceramics. The laser Raman study reveals distorted MoO42− tetrahedral networks in the unit cell of the BaCe2(MoO4)4 ceramics. The BaCe2(MoO4)4 exhibits a dielectric constant of 12.3, an unloaded quality factor of 3320, and a temperature coefficient of resonant frequency of −37 ppm/°C.

Possible viral involvement in human mammary carcinoma: A microwave and laser-raman study

The microwave and laser-Raman spectra of normal human mammary and mammary carcinoma cells indicate that resonances between 1010 and 1012 Hz exist in active cells. The spectra of both “normal” and carcinoma cells, from the same patients, displayed a splitting of the single spectra peaks seen in the spectra of normal cells. This same splitting of peaks was observed also when BHK cells, in tissue culture, were transformed into tumor cells by sarcoma viruses. The result suggests that in vivo coherent oscillations become resolved during the oncogenic process. In addition, females who later suffer mammary carcinoma may carry a latent oncogenic virus which becomes induced by pregnancy, menopause, and trauma. Thus mammary carcinoma, and indeed predisposition to the disease, may be diagnosed by the spectroscopic methods described.

Characterization of p-type In–Sb thin films prepared by vacuum evaporation

Thin films of InSb have been prepared onto well-cleaned glass substrates at different substrate temperatures (303, 473 and 523 K) by vacuum evaporation. The elemental composition of the deposited InSb films was evaluated by Auger electron spectroscopy (AES) and it was found to be 24% (In) and 76% (Sb). X-ray diffraction patterns indicated the polycrystalline nature of the InSb films with preferential orientation along (1 1 1) plane. Particle size ( D), dislocation density ( δ ) and strain ( ε ) were determined from the XRD patterns. The particle size increases with the increase of substrate temperature, which was found to be in the range from 8.31 to 24.95 nm. In Laser Raman study, the presence of longitudinal mode (LO) confirms that the deposited films were having crystalline nature. Hall measurements indicate that the films were p-type, having carrier concentration ≅ 10 16 cm −3 and mobility (1.1–6.5)×10 3 cm 2/V s.

Influence of substrate temperature on the properties of vacuum evaporated InSb films

AbstractIndium Antimonide (InSb) thin films were grown onto well cleaned glass substrates at different substrate temperatures (303, 373 and 473 K) by vacuum evaporation. The elemental composition of the deposited InSb film was found to be 52.9% (In) and 47.1% (Sb). X‐ray diffraction studies confirm the polycrystallinity of the films and the films show preferential orientation along the (111) plane. The particle size (D), dislocation density (δ) and strain (ε) were evaluated. The particle size increases with the increase of substrate temperature, which was found to be in the range from 22.36 to 32.59 nm. In Laser Raman study, the presence of longitudinal mode (LO) confirms that the deposited films were having the crystalline nature. Raman peak located at 191.26 cm–1 shift towards the lower frequencies and narrows with increase in deposition temperature. This indicates that the crystallinity is improved in the films deposited at higher substrate temperatures. Hall measurements indicate that the films were p‐type, having carrier concentration ≅1016 cm–3 and mobility (4–7.7) ×103 cm2/Vs. It is observed that the carrier concentration (N) decreases and the Hall mobility (μ) increases with the increase of substrate temperature. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A comparative laser Raman study on TB4A, TB7A and TB10A

The basic structural differences between three thermotropic liquid crystals TB4A, TB7A and TB10A have been interpreted by analysing their Raman spectra. Three spectral regions, 925-1025, 1275-1475 and 1525-1650 cm-1, have been chosen in this context to incorporate their structural dissimilarity. The induced planarity of the backbone, as an effect of increasing chain length, has been studied by observing the changes in the respective Raman spectra of the three compounds. A tentative assignment of all the modes observed in the region 400-1700cm-1 is made in this context. The molecular conformations of the three compounds have been predicted in their solution states, and are compared with the molecular environment that exists in their liquid crystalline states. Structural disorder at the solid-SmG transition is discussed and the changes are incorporated systematically.

Laser raman study of interaction between microclusters of AgI and HgI 2

Laser Raman spectrum of the product of interaction between nanoparticles of AgI and HgI 2 has been studied. The close resemblance of this spectrum with that of the laser Raman spectrum of crystalline Ag 2HgI 4 indicates that interaction has taken place between nanoparticles of AgI and HgI 2.

A laser Raman study of D+ and He+ ion irradiated diamond and graphite

Type Ib diamond and highly orientated graphite were irradiated with 25 keV D+ or He+ ions at room temperature to several doses, and examined by laser Raman spectroscopy. The absolute intensity of the diamond peak at 1330 cm−1 gradually decreased with increasing dose, finally disappeared at a critical dose, and a very broad peak appeared instead, indicating an amorphization of the diamond. Though the critical dose for D+ was larger than that for He+, the critical dpa calculated by energy deposition for both ions was nearly the same, which means the chemical effect of implanted species on the amorphization is negligible. Nevertheless, a certain difference was observed in the broad Raman spectra of the amorphized specimen between the D+ and He+ irradiation. The Raman spectrum of the D+ irradiated diamond was quite similar to that of amorphous hydrogenated carbon (a-C:H) and a Raman component, which is due to C-D bond formation, appeared at around 1550 cm−1 only for the D+ irradiated diamond. A similar spectrum was also seen in the amorphized graphite by D+ irradiation. This leads us to conclude that the amorphized structures of diamond and graphite under D+ irradiation are very similar to that of a-C:H.

Structural effects of the C2-methylhypoxanthine:cytosine base pair in B-DNA: A combined NMR and X-ray diffraction study of d(CGC[m2I]AATTCGCG).

C2-Methylhypoxanthine (m2I) is a synthetic analog of guanine with the N2-amino group replaced by a methyl group. We have studied the structural consequence of the m2I incorporation in DNA by a combination of X-ray crystallographic, NMR, and enzymatic analyses. The crystal structure of d(CGC[m2I]AATTCGCG) has been solved and refined to an R factor of 20.7% at 2.25-A resolution. In the DNA duplex, the two independent m2I:C base pairs maintain the Watson-Crick scheme. While the C2-methyl group of m2I is in van der Waals contact with the O2 of the base-paired cytosine, it only causes the base pair to have slightly higher propeller twist and buckle angles. Its solution structure was analyzed by the NMR refinement procedure SPEDREF [Robinson, H., & Wang, A. H.-J. (1992) Biochemistry 31, 3524-3533] using 2D nuclear Overhauser effect data. Two starting models, a relaxed fiber model and an X-ray model, were subjected to the NOE-constrained refinement using 1518 NOE cross-peak integrals to arrive at the final models with (NOE) R factors of 13.8% and 14.3%, respectively. The RMSD between the two refined models (all atoms included) is 1.23 A, which presently seems to be near the limit of convergence of NOE-based refinement. The local structures of the two models are in better agreement as measured by the RMSD of the dinucleotide steps, falling in the range 0.54-0.98 A. Both refined solution structures confirm that the m2I dodecamer structure is of the B-DNA type with a narrow minor groove at the AT region, as observed in the crystal. However, significant differences exist between the crystal and solution structures in parameters such as pseudorotation angles, propeller twist angles, etc. The solution structure tends to have a more uniform backbone conformation, an observation consistent with that concluded from the laser Raman study of d(CGCAAATTTGCG) [Benevides, J. M., Wang, A. H.-J., van der Marel, G. A., van Boom, J. H., & Thomas, G. J., J. (1988) Biochemistry 27, 931-938]. Three related dodecamers, d(CGCGAATTCGCG), d(CGC[m2I]AATTCGCG), and d(CGC[e6G]AATTCGCG), were tested as substrates for the restriction endonuclease EcoRI. The m2I dodecamer was active, but the e6G dodecamer was not. Our results illustrate the complementarity in terms of the structural information provided by the two methods, X-ray diffraction and NMR.

Inhibiting effect of AlPO4 and SiO2 on the anatase → rutile transformation reaction: An x-ray and laser Raman study

The anatase → rutile transformation reaction of TiO2 prepared in contact with amorphous aluminum phosphate and with fume silica has been investigated as a function of temperature by x-ray diffraction methods. It is observed that the anatase → rutile transformation in such systems becomes greatly inhibited and the Raman spectra of titania on such surfaces exhibit features that indicate substrate-TiO2 interfacial reactions.

In situ laser Raman study of the effect of water on undoped and caesium-doped silica-supported 12-molybdophosphoric acid catalysts

The surface chemistry of silica-supported 12-molybdophosphoric acid (HPMo) catalysts and the caesium salts, in dehydrated and hydrated form, has been investigated by laser Raman spectroscopy (LRS). The Raman spectra were observed to be dependent on both the pretreatment temperature and the environment of the sample during heating. A sample containing 23 wt.% HPMo, equivalent to 0.12 of the molybdophosphate anions (Keggin unit, KU) per nm2, a loading only marginally greater than the monolayer loading found from X-ray photoelectron spectroscopy (XPS), produced an unidentified species and/or MoO3 on heating to temperatures higher than 300 °C. Upon exposure to water vapour, the unknown species is reconverted to the KU. With loadings of HPMo less than the monolayer equivalent no decomposition into MoO3 is observed at temperatures up to 550 °C. The stable species found on the silica surface after heating is believed to be the dehydrated or defect KU formed on removal of an oxygen ion in the process of the desorption of water.

Laser Raman study of the low-temperature phase transformation in [N(CH3)4]2CuCl4 single crystals

Abstract The results of a detailed temperature-dependent Raman study of single crystals of [N(CH 3 ) 4 ] 2 CuCl 4 are reported in different spectral regions. The observed splittings of the symmetric stretching modes of the N(CH 3 ) + 4 ion below 250 K and the CuCl 2− 4 ion below 50 K into doublets have been explained as being due to the presence of ions on two energetically inequivalent positions within the lattice. From a temperature dependence of the half-widths, frequency separation, relative intensities of the two components of the CN stretch and other thermosensitive spectral changes, we have discovered a new first order type phase transition in this system at ∼50 K due to ordering of ions from one configuration to another. The reordering in phase IV up to 50 K takes place via continuous movement of cations from the disordered to ordered configuration, but below 50 K the ions freeze in the two inequivalent configurations. The dynamics of ordering of the ions at different temperatures is discussed in this communication.

Organic pesticides modify lipid-lipid and lipid-protein domains in model membranes. A laser Raman study

The effect of hexachlorocyclohexane (all isomers) on the thermal transition properties of phospholipid liposomes was determined by Raman spectroscopy. Raman spectra of liposomes with and without the presence of hexachlorocyclohexanes were recorded in the C-H stretching region which shows three major bands around 2850, 2880 and 2930 cm −1. Thermal transition properties were estimated from plots of I 2880 I 2850 and or I 2930 I 2850 vs. temperature, where I represents the intensity of the respective band. Our data on phospholipid liposomes reveal that δ- and γ-hexachlorocyclohexanes drastically reduce and broaden the main thermal transitions of phospholipids at toxic level concentrations. These effects are more pronounced in liposomes containing 18 or more carbon atom long acyl chains. α- and β-isomers at similar concentrations show a minimum effect on the thermal transition properties of phospholipids. Raman analysis of phospholipid liposomes containing melittin, interestingly, reveal that the δ-isomer unlike the γ-isomer strongly alters the transition properties of boundary lipids. These data suggest that the effect of hexachlorocyclohexanes on the thermal transition properties of membranes is stereo specific and that the δ-isomer preferably disrupts the lipid-protein domains. Results are explained on the basis of the dynamic flexibility owing to the equatorial and axial chlorine atoms of various hexachlorocyclohexane isomers.

Laser Raman study of single crystals of deuterated cadmium fluorosilicate

A laser Raman study of oriented single crystals of CdSiF 6:6D 2O at room temperature as well as at 10 K in all the six polarization geometries has been made. Also a detailed temperature dependent Raman study from room temperature to 10 K in ( yy) polarization in the region of internal vibrations and lattice modes has been made. Abrupt changes have been observed in frequency shift, line-width and intensity of some of the bands at about 235 K. Some doubly degenerate modes show splitting at the same temperature. From these observations a phase change at about 235 K is inferred for this salt. It has been suggested that when the system is cooled, the lattice contracts and the water molecules lose their reorientational freedom to some extent which might result in the distortion of the [Cd(OD 2) 6] 2+ octahedra triggering a phase transition.

Laser Raman study of lattice modes of high temperature tetragonal to cubic transition in ammonium nitrate

The temperature dependence of the Raman spectra of ammonium nitrate in the lattice mode region below 200 cm −1 has been measured at high temperatures through the tetragonal II to cubic I phase transition at 398 K. As the II–I transition is approached a pronounced softening of the librational mode is observed as well as an increase in the line width.

Laser Raman study of phase transitions in [N(CH3)4]2COCl4 single crystals

AbstractTemperature‐dependent Raman spectra of oriented single crystals of [N(CH3)4]2CoCl4 are reported. An assignment of the observed Raman bands has been made and it was found that the N(CH3)4+ and CoCl42− groups occupy sites of Cs symmetry in the lattice at room temperature. However, because of rapid reorientation, the CoCl42− groups retain an effective tetrahedral symmetry. The prototypic to incommensurate to commensurate phase transitions are associated with the orientational dynamics of the CoCl4 tetrahedra. The monoclinic to orthorhombic super lattice phase transition at 122 K in [N(CH3)4]2CoCl4 is triggered by the distortion of the N(CH3)4+ groups in the lattice.

Laser Raman study of phase transformation in single crystals of cadmium fluorotitanate hexahydrate

AbstractA detailed temperature‐dependent Raman study of oriented single crystals of CdTiF6·6H2O down to 10 K was carried out in the regions of internal vibrations and lattice modes. The line width, frequency shift and intensities of the modes associated with the [Cd(H2O)6]2+ and [TiF6]2− octahedra show abrupt changes at temperatures around 200 and 80 K, respectively, and many doubly degenerate modes split into two components. These studies suggest that this system undergoes two structural phase transitions at 200 and 80 K. A mechanism for these phase transitions is suggested.