Near infrared spectroscopy of stearic acid adsorbed on montmorillonite

The adsorption of stearic acid on both sodium montmorillonites and calcium montmorillonites has been studied by near infrared spectroscopy complimented with infrared spectroscopy. Upon adsorption of stearic acid on Ca–Mt additional near infrared bands are observed at 8236 cm^?1 and is assigned to an interaction of stearic acid with the water of hydration. Upon adsorption of the stearic acid on Na–Mt, the NIR bands are now observed at 5671, 5778, 5848 and 5912 cm^?1 and are assigned to the overtone and combination bands of the CH fundamentals. Additional bands at 4177, 4250, 4324, 4337, 4689 and 4809 cm^?1 are attributed to CH combination bands resulting from the adsorption of the stearic acid. Stearic acid is used as a model molecule for adsorption studies. The application of near infrared spectroscopy to the study of this adsorption proved most useful.     

Thermal properties of Co-, Ni- and Cu-exchanged montmorillonite with 3-hydroxypyridine

Thermal analysis (TG, DTG), powder diffraction analysis (RTG) and infrared absorption spectra (IR spectra) were used to study of release of 3-hydroxypyridine (3-OHpy) from Co-, Ni- and Cu-exchanged montmorillonite (Co-MMT, Ni-MMT, Cu-MMT). It was found that release of 3-OHpy under heating from Co- and Ni-MMT proceeds in three distinct steps while from Cu-MMT in four steps. The first step can be assigned to the release of physically sorbed 3-OHpy while the last one corresponds to the lattice dehydroxylation. The second step (Co-, Ni-MMT) and/or second and third steps (Cu-MMT) can be assigned to release of chemically bonded 3-OHpy. This investigation shows that studied exchanged montmorillonites predominantly exhibit Lewis acid character. This revised version was published online in August 2006 with corrections to the Cover Date.     

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 1440cm(-1) is assigned to the nu(3) CO(3)(2-) antisymmetric stretching vibration. An additional band is resolved at 1335cm(-1). An intense sharp Raman band at 1092cm(-1) is assigned to the CO(3)(2-) symmetric stretching vibration. Infrared emission spectra show a broad antisymmetric band at 1442cm(-1) shifting to lower wavenumbers with thermal treatment. A band observed at 870cm(-1) with a band of lesser intensity at 842cm(-1) shifts to higher wavenumbers upon thermal treatment and is observed at 865cm(-1) at 400 degrees C and is assigned to the CO(3)(2-)nu(2) mode. No nu(2) bending modes are observed in the Raman spectra for smithsonite. The band at 746cm(-1) shifts to 743cm(-1) at 400 degrees C and is attributed to the CO(3)(2-)nu(4) in phase bending modes. Two infrared bands at 744 and around 729cm(-1) are assigned to the nu(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 2991cm(-1) in both the IE and infrared spectra are attributed to combination bands.     

Time-resolved Fourier transform infrared emission spectroscopy of laser ablation products

Time-resolved Fourier transform infrared spectroscopy was applied for observations of emission spectra from ablation products induced by a Nd:YLF laser with a 2.5 kHz repletion rate. The infrared emission spectra from Fe, Cu, Zn, and Al atoms were observed in the 2.5–5 μm region. The observed emission spectrum from iron ablation in the 2500 cm⁻¹ region agrees very well with solar absorption spectrum, where new lines have been detected in the present experiment in addition to the lines observed from a hollow cathode discharge. When O₂ was added to the carbon ablation, emissions from vibrationally excited CO were observed with non-equilibrium vibrational distribution.     

Mid-infrared spectroscopy of molecular ions in helium nanodroplets

High resolution IR spectra of aniline, styrene, and 1,1-diphenylethylene cations embedded in superfluid helium nanodroplets have been recorded in the 300-1700 cm(-1) range using a free-electron laser as radiation source. Comparison of the spectra with available gas phase data reveals that the helium environment induces no significant matrix shift nor leads to an observable line broadening of the resonances. In addition, the IR spectra have provided new and improved vibrational transition frequencies for the cations investigated, as well as for neutral aniline and styrene. Indications have been found that the ions desolvate from the droplets after excitation by a non-evaporative process in which they are ejected from the helium droplets. The kinetic energy of the ejected ions is found to be ion specific and to depend only weakly on the excitation energy.     

Gas-phase photodissociation of CH3COCN at 308 nm by time-resolved Fourier-transform infrared emission spectroscopy

By using time-resolved Fourier-transform infrared emission spectroscopy, the fragments of HCN(v = 1, 2) and CO(v = 1-3) are detected in one-photon dissociation of acetyl cyanide (CH(3)COCN) at 308 nm. The S(1)(A(")), (1)(n(O), π(?) (CO)) state at 308 nm has a radiative lifetime of 0.46 ± 0.01 μs, long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of Ar collision-induced internal conversion is estimated to be (1-7) × 10(-12) cm(3) molecule(-1) s(-1). The measurements of O(2) dependence exclude the production possibility of these fragments via intersystem crossing. The high-resolution spectra of HCN and CO are analyzed to determine the ro-vibrational energy deposition of 81 ± 7 and 32 ± 3 kJ∕mol, respectively. With the aid of ab initio calculations, a two-body dissociation on the energetic ground state is favored leading to HCN + CH(2)CO, in which the CH(2)CO moiety may further undergo secondary dissociation to release CO. The production of CO(2) in the reaction with O(2) confirms existence of CH(2) and a secondary reaction product of CO. The HNC fragment is identified but cannot be assigned, as restricted to a poor signal-to-noise ratio. Because of insufficient excitation energy at 308 nm, the CN and CH(3) fragments that dominate the dissociation products at 193 nm are not detected.     

Field emission spectroscopy

The first experimental evidence of the existence of electron states localised on a clean metal surface was available to us since 1967 in the form of the well known Swanson-Crouser hump in the energy distribution of electrons field-emitted from the W(100) plane, although it took some time before its interpretation as such, in 1976, was established beyond any doubt. Subsequently, angle-resolved photoemission proved to be a more competitive method for the investigation of surface states of metals and semiconductors. However, field emission remains a useful tool in surface physics research.

After a brief introduction to field emission spectroscopy, we review recent work which shows the potentiality of this technique in the investigation of the surface properties of semiconductors, ferromagnetic metals, thermal superconductors, and of the electronic structure of supported clusters.     

Photofield emission spectroscopy

A brief review of the investigations of optical excitations in the bulk and on the surfaces of metals by the photofield emission method is presented. The selected results show that the method is very useful for detailed penetration of band structure near the Fermi level. Examples for bulk band structures and surface density of states of tungsten, tantalum and titanium are presented and compared with theoretical results. The residual gas effect on surface states is described and discussed. Taking into consideration the thermocurrent produced by light radiation, a new and more detailed presentation of surface states observed for titanium (0001) face is shown as the density of states. The method of energy distribution of photofield emitted electrons is briefly mentioned. The inverse and two-photon photoemission methods are mentioned.     

Mid-infrared second-order susceptibility of alpha-quartz and its application to visible-infrared surface sum-frequency spectroscopy

We provide the first account of the second-order susceptibility of quartz down to 10 mum (1000 cm(-1)) and show how this data may be used along with the sum-frequency response of an amorphous gold surface to elucidate the nonlinear susceptibility of any material in the mid-infrared region. Crystalline quartz is an established material for use in second-harmonic and sum-frequency generation studies of new systems, on account of its well-characterized linear and nonlinear optical properties. Previous knowledge of its nonlinear susceptibility has been limited to its transparent region, wavelengths shorter than about 3 mum. Longer wavelength chi((2)) values for quartz are particularly important for techniques such as vibrational sum-frequency spectroscopy which are expanding into the mid-IR with the increasing availability of widely tunable infrared laser sources.     

Determination of chlorinated hydrocarbons introduced into air/acetylene flames by Fourier transform infrared emission spectroscopy

A Fourier transform spectrometer is used to record the infrared emission from chlorinated hydrocarbons combusted in an air/acetylene flame. In this manner, the chlorinated hydrocarbons are determined by monitoring the infrared emission of hydrogen chloride at 2653 cm(-1). Discussion is presented of the air/acetylene flame background, and the potential spectral interference from the emission of deuterated species. Practical detection limits for chloroform, carbon tetrachloride and methylene chloride in acetone, methanol, and ethanol are solvent independent and are found to be 1.1, 0.80, and 1.0%, respectively. Calibration curves for these three analytes are linear from their detection limits to approximately 55% (v/v). In addition, evidence is presented that flame flicker-noise does not lead to a multiplex disadvantage when the Fourier transform instrument is used for data acquisition.     

Use of near infrared emission spectroscopy in the study of supporting materials and stationary phases for liquid chromatography

Near infrared emission spectroscopy (NIRES) has been investigated in the study of different materials employed in liquid chromatography. The samples were heated in a nitrogen atmosphere and the emission spectra were obtained using a lab-made NIRES instrument. Through principal component analysis (PCA) using the raw emission spectra, it was possible to distinguish different materials according to their physical and/or chemical characteristics. Linear relationships between emissivity spectra and the contents of the coating material or the specific surface areas was observed for stationary phases or bare silicas, respectively. Furthermore, the thermal stability of stationary phases could be followed in real time.     

Mid-infrared spectroscopy for detection of Huanglongbing (greening) in citrus leaves

In recent years, Huanglongbing (HLB) also known as citrus greening has greatly affected citrus orchards in Florida. This disease has caused significant economic and production losses costing about $750/acre for HLB management. Early and accurate detection of HLB is a critical management step to control the spread of this disease. This work focuses on the application of mid-infrared spectroscopy for the detection of HLB in citrus leaves. Leaf samples of healthy, nutrient-deficient, and HLB-infected trees were processed in two ways (process-1 and process-2) and analyzed using a rugged, portable mid-infrared spectrometer. Spectral absorbance data from the range of 5.15-10.72 μm (1942-933 cm⁻¹) were preprocessed (baseline correction, negative offset correction, and removal of water absorbance band) and used for data analysis. The first and second derivatives were calculated using the Savitzky-Golay method. The preprocessed raw dataset, first derivatives dataset, and second derivatives dataset were first analyzed by principal component analysis. Then, the selected principal component scores were classified using two classification algorithms, quadratic discriminant analysis (QDA) and k-nearest neighbor (kNN). When the spectral data from leaf samples processed using process-1 were used for data analysis, the kNN-based algorithm yielded higher classification accuracies (especially nutrient-deficient leaf class) than that of the other spectral data (process-2). The performance of the kNN-based algorithm (higher than 95%) was better than the QDA-based algorithm. Moreover, among different types of datasets, preprocessed raw dataset resulted in higher classification accuracies than first and second derivatives datasets. The spectral peak in the region of 9.0-10.5 μm (952-1112 cm⁻¹) was found to be distinctly different between the healthy and HLB-infected leaf samples. This carbohydrate peak could be attributed to the starch accumulation in the HLB-infected citrus leaves. Thus, this study demonstrates the applicability of mid-infrared spectroscopy for HLB detection in citrus.     

Infrared and infrared emission spectroscopy of gallium oxide α-GaO(OH) nanostructures

Infrared spectroscopy has been used to study nano- to micro-sized gallium oxyhydroxide α-GaO(OH), prepared using a low temperature hydrothermal route. Rod-like α-GaO(OH) crystals with average length of 2.5 μm and width of 1.5 μm were prepared when the initial molar ratio of Ga to OH was 1:3. β-Ga₂O₃ nano and micro-rods were prepared through the calcination of α-GaO(OH). The initial morphology of α-GaO(OH) is retained in the β-Ga₂O₃ nanorods.The combination of infrared and infrared emission spectroscopy complimented with dynamic thermal analysis were used to characterise the α-GaO(OH) nanotubes and the formation of β-Ga₂O₃ nanorods. Bands at around 2903 and 2836 cm⁻¹ are assigned to the –OH stretching vibration of α-GaO(OH) nanorods. Infrared bands at around 952 and 1026 cm⁻¹ are assigned to the Ga–OH deformation modes of α-GaO(OH). A significant number of bands are observed in the 620–725 cm⁻¹ region and are assigned to GaO stretching vibrations.     

Raman and infrared spectroscopy of selected vanadates

Raman and infrared spectroscopy has been used to study the structure of selected vanadates including pascoite, huemulite, barnesite, hewettite, metahewettite, hummerite. Pascoite, rauvite and huemulite are examples of simple salts involving the decavanadates anion (V10O28)6-. Decavanadate consists of four distinct VO6 units which are reflected in Raman bands at the higher wavenumbers. The Raman spectra of these minerals are characterised by two intense bands at 991 and 965 cm(-1). Four pascoite Raman bands are observed at 991, 965, 958 and 905 cm(-1) and originate from four distinct VO6 sites. The other minerals namely barnesite, hewettite, metahewettite and hummerite have similar layered structures to the decavanadates but are based upon (V5O14)3- units. Barnesite is characterised by a single Raman band at 1010 cm(-1), whilst hummerite has Raman bands at 999 and 962 cm(-1). The absence of four distinct bands indicates the overlap of the vibrational modes from two of the VO6 sites. Metarossite is characterised by a strong band at 953 cm(-1). These bands are assigned to nu1 symmetric stretching modes of (V6O16)2- units and terminal VO3 units. In the infrared spectra of these minerals, bands are observed in the 837-860 cm(-1) and in the 803-833 cm(-1) region. In some of the Raman spectra bands are observed for pascoite, hummerite and metahewettite in similar positions. These bands are assigned to nu3 antisymmetric stretching of (V10O28)6- units or (V5O14)3- units. Because of the complexity of the spectra in the low wavenumber region assignment of bands is difficult. Bands are observed in the 404-458 cm(-1) region and are assigned to the nu2 bending modes of (V10O28)6- units or (V5O14)3- units. Raman bands are observed in the 530-620 cm(-1) region and are assigned to the nu4 bending modes of (V10O28)6- units or (V5O14)3- units. The Raman spectra of the vanadates in the low wavenumber region are complex with multiple overlapping bands which are probably due to VO subunits and MO bonds.     

Rapid discrimination of Eurycoma longifolia extracts by Fourier transform infrared spectroscopy and two dimensional correlation infrared spectroscopy

Eurycoma longifolia is a herbal medicinal plant of South-East Asian origin, popularly recognized as ‘Tongkat Ali’. The root extracts have been used in indigenous traditional medicines for its unique antimalarial, anti-pyretic, antiulcer, cytotoxic and aphrodisiac properties. It is an important task that fast and effective analysis methods monitor the inherent qualities of traditional herbal medicines and its corresponding extracts products as a complicated mixture system. Owing to the unique fingerprint character and extensive applicability to test sample, infrared spectral method have been used in many research fields. In this paper, we use FT-IR, second derivative infrared spectroscopy and two-dimensional correlation infrared spectroscopy (2D-IR) step by step to analyze E. longifolia and its different extracts (extracted by hexane, ethyl acetate, dichloromethane and methanol in turn). The findings indicated that FT-IR and 2D-IR can provide many holistic variation rules of chemical constituents. The structural information of the samples indicated that E. longifolia and its extracts contain a large amount of quassinoids, since some characteristic absorption peaks of quassinoids, such as ∼1700 cm⁻¹, ∼1670 cm⁻¹, ∼1600 cm⁻¹,∼1500 cm⁻¹, and ∼1270 cm⁻¹ can be detected. This method, having its high resolution and excellent macroscopic fingerprint features, can not only supply lots of structural information of main components in the complicated system, but also can differentiate the tiny differences between the similar systems according to the macro-fringerprint characters. This method is highly rapid, effective, accurate and well repetitive for pharmaceutical research.     

Nanofoam porosity by infrared spectroscopy

Infrared spectroscopy has been used to determine the porosity of polymer nanofoams produced from block copolymers of an aromatic polyimide with either poly(propylene oxide) or poly(α-methyl styrene). It is shown that, with an independent measurement of the film thickness, both the absorption bands and the interference fringes can yield an accurate measure of the void content. The results obtained are in quantitative agreement with density gradient methods. © 1995 John Wiley & Sons, Inc.     

Diffuse-reflectance spectroscopy in the infrared

The theory, and the problems encountered in the development of diffuse-reflectance spectroscopy in the infrared region as an analytical technique, are reviewed. The introduction of Fourier-transform infrared spectrometers has eliminated the difficulty of detecting small scattered intensities, and diffuse-reflectance measurement is now a routine method. The first commercial instruments are now available.     

Polarization fourier transform infrared spectroscopy

Some Fourier transform infrared spectroscopic studies with linearly and circularly polarized radiation are reported. They were all carried out by means of the differential technique, consisting in the comparison of two single-channel spectra of opposite polarization. Thus, linear dichroic or circular dichroic spectra with positive and negative bands were recorded. Typical application examples of both techniques are presented.