Laser Raman and infra-red spectra of biomolecule: 5-aminouracil

Laser Raman (200–4000 cm⁻¹) and IR (200–4000 cm⁻¹) spectra of 5-aminouracil were recorded in the region 200–4000 cm⁻¹. Assuming a planar geometry and C_s point group symmetry, it has been possible to assign all the 36 (25a′ + 11a″) normal modes of vibration for the first time. The two NH bonds of the NH₂ group appear to be equivalent as the NH₂ stretching frequencies satisfy the empirical relation proposed for the two equivalent NH bonds of the NH₂ group. The two NH₂ stretching frequencies are distinctly separated from the CH/NH ring stretching frequencies. A strong and sharp IR band at 3360 cm⁻¹ could be identified as the anti-symmetric NH₂ mode whereas the band at 3290 cm⁻¹ with smaller density could be identified as the symmetric NH₂ stretching mode. All other bands have also been assigned different fundamentals/overtones/combinations.      

Pulsed quantum-cascade-laser spectroscopy with intermediate-size pulses: application to NH3 in the 10 μm region

Pulsed quantum-cascade-laser spectrometers are usually used to detect atmospheric gases with either the interpulse technique (short pulses, typically 5–20 ns) or the intrapulse technique (long pulses, typically 500–800 ns). Each of these techniques has its drawbacks. Particularly the gas absorption spectra are generally distorted. We have previously developed another technique called intermediate-size pulses (typically 50–100 ns) technique for gas detection using pulsed QCL spectrometers. In this paper, infrared spectra of ammonia recorded with this technique in the 10 μm region are presented. For the NH₃ spectra recorded at low pressure (i.e. in the mbar range), the spectra show typical oscillations after the absorption. The Beer–Lambert law cannot explain these oscillations, termed the rapid-passage effect. Comparisons between experimental and calculated spectra will be realized. This phenomenon is not satisfactory from a spectroscopic point of view and spectra must be recorded at higher pressures. For the NH₃ spectra recorded at higher pressure (i.e. in the 50 mbar range), the oscillations disappear and the Beer–Lambert law could be reused. This paper will demonstrate that the intermediate-size technique gives reliable measurements for NH₃ detection. Moreover the typical apparatus function (0.003 cm⁻¹ HWHM) is far lower from the typical apparatus function of the interpulse QCL spectrometers (0.015 cm⁻¹ HWHM).     

Infrared absorption spectra of pure and doped YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> single crystals

Several weak absorption bands have been observed in the optical absorption spectra of pure and rare-earth-doped YAl₃(BO₃)₄ single crystals in the 3350– 3650 cm⁻¹ wave number region. Two of them, peaking at about 3377 cm⁻¹ and 3580 cm⁻¹ in the 8 K spectra, appear in most of the samples. They are tentatively attributed to the stretching mode of OH⁻ ions incorporated in the crystal during the growth. An additional absorption band at about 5250 cm⁻¹ at 8 K has also been detected in almost all samples. The temperature and polarization dependences of these bands, and their possible origin, are discussed.     

Influence of post-grown Li-rich and Li-poor vapor transport equilibration on composition, OH− absorption and optical-damage threshold of Mg (5 mol%) : LiNbO3 crystals

Li-rich (Li-poor) vapor transport equilibration (VTE) treatments on a number of Z-cut 0.47 mm thick congruent MgO (5 mol% in melt) : LiNbO₃ crystals were carried out at 1100°C over different durations ranging in 1–172 (40–395) h. Neutron activation analysis shows that neither Li-rich nor Li-poor VTE-induced Mg and Nb loss from the crystal occurred. The Li₂O content in the crystal was measured as a function of VTE duration by the gravimetric method. The Li-rich/Li-poor VTE effects on OH⁻ absorption were studied in comparison with the as-grown crystal. The study shows that the Li-rich VTE results in OH⁻ absorption band annihilation. After further oxidation treatment the band reemerges and peaks at the same wavenumber as that of the as-grown crystal (∼3535.6 cm⁻¹), showing that the MgO concentration in the Li-rich VTE crystal is still above the optical-damage threshold. The Li-poor VTE causes OH⁻ band shift to 3486.3–3491.6 cm⁻¹, indicating that the MgO concentration in all Li-poor VTE crystals is all below the optical-damage threshold. Further successive Li-rich VTE and oxidation treatments on the Li-poor VTE-treated crystal lead the band to shift back to 3535.6 cm⁻¹, showing that the post Li-rich VTE brought the Li-poor VTE-treated crystal above the optical-damage threshold again. It is found that the peaking position, band width, peaking absorption and band area of the absorption at ∼3486 cm⁻¹ all increase monotonously with the decrease of the Li₂O content arising from prolonged Li-poor VTE, and quantitative relationships to the Li₂O content are established for the latter two parameters. The VTE effects on the OH⁻ absorption are conducted with the VTE-induced OH⁻ content alteration and charge redistribution.     

Optical and IR study of Li2O–CuO–P2O5 glasses

Infrared (IR) and UV spectra of ternary Li₂O–CuO–P₂O₅ glasses in two series Li₂O(65−X)%–CuO(X%)–P₂O₅(35%), X = 20, 30, 40 and Li₂O(55−X)%–CuO(X%)–P₂O₅(45%), X = (10, 20, 30) were studied. Infrared (IR) investigations showed the metaphosphate and pyrophosphate structures and with increase of CuO content in metaphosphate glass, the skeleton of metaphosphate chains is gradually broken into short phosphate groups such as pyrophosphate. IR spectra showed one band at about 1,220 and 1,260 cm⁻¹ for P₂O₅(35%) and P₂O₅(45%) series, respectively, assigned to P=O bonds. For CuO additions ≤20 mol%, the glasses exhibit two bands in the frequency range 780–720 cm⁻¹ which are attributed to the presence of two P–O–P bridges in metaphosphate chain. But for CuO addition ≥30 mol%, the glasses exhibit only a single band at 760 cm⁻¹ which is assigned to the P–O–P linkage in pyrophosphate group. In optical investigations, absorption coefficient versus photon energy showed three regions: low energy side, Urbach absorption, and high energy side. In Urbach’s region, absorption coefficient depends exponentially on the photon energy. At high energy region, optical gap was calculated and investigations showed indirect transition in compounds and decreases in optical gap with increases of copper oxides contents that is because of electronic transitions and increasing of nonbridging oxygen content.     

Wavelength modulation and cavity enhanced absorption spectroscopy using ～1.9?μm radiation produced by difference frequency generation with a MgO doped PPLN crystal

We have demonstrated the production of ∼1.9 μm near-infrared radiation by using difference frequency generation within a 5% MgO doped PPLN crystal by coupling ∼735 nm radiation from a tunable external cavity diode laser with relatively high powered 532 nm radiation from both Nd:YVO₃ and Nd:YAG lasers. The radiation produced is of low power, ∼15 μW, and was used in conjunction with the sensitivity enhancing techniques of wavelength modulation spectroscopy (WMS) and cavity enhanced absorption spectroscopy (CEAS). Experiments were carried out on rotationally resolved transitions in the combination bands of NH₃ and CO₂ in the 1.9 μm region. An α _min value of 3.6×10⁻⁶ cm⁻¹ Hz^−1/2 was achieved for WMS measurements on CO₂. A comparable α _min value of 2.2×10⁻⁶ cm⁻¹ Hz^−1/2 was achieved for NH₃ using CEAS. The low NIR power indicates that despite the level of MgO doping quoted for the crystal, under prolonged exposure photorefractive damage has occurred.     

FTIR spectra of plasticized high molecular weight PVC–LiCF3SO3 electrolytes

Fourier transform infrared spectroscopy studies have been conducted to investigate the interaction among components in a system of high molecular weight polyvinylchloride (PVC)–lithium trifluoromethanesulfonate (LiCF₃SO₃) incorporated with different type of plasticizers, namely, ethylene carbonate (EC), propylene carbonate (PC), and dibutylphthalate (DBP). Interaction between PVC and LiCF₃SO₃ was confirmed by C–H rocking mode at 1,255 cm⁻¹ for PVC shift to 1,252 cm⁻¹ in PVC–LiCF₃SO₃. The plasticizers’ carbonyl (C=O) oxygen atom which carries lone pair electrons interact with Li⁺ of LiCF₃SO₃ and methine hydrogen of PVC in LiCF₃SO₃–plasticizer system and PVC–plasticizer system, respectively. Changes in peaks assigned to 1,264 cm⁻¹ (ν _as(SO₃)), 1,033 cm⁻¹ (ν _s(SO₃)), 1,181 cm⁻¹ (ν _as(CF₃)), 1,230 cm⁻¹ (ν _s(CF₃)), 765 cm⁻¹ (δ _s(CF₃)), 644 cm⁻¹ (δ _s(SO₃)), 578 cm⁻¹ (δ _as(CF₃)), and 519 cm⁻¹ (δ _as(SO₃)) indicate the occurrence of complexation in the PVC–LiCF₃SO₃ system, LiCF₃SO₃–plasticizer system, and PVC–LiCF₃SO₃–plasticizer system.     

Measurements of the temperature and water vapor concentration in a hot zone by tunable diode laser absorption spectrometry

A tunable diode laser absorption spectroscopy (TDLAS) technique and appropriate instrumentation was developed for the measurement of temperature and water vapor concentrations in heated gases. The technique is based on the detection of the spectra of H₂O absorption lines with different energies of low levels. The following absorption lines of H₂O were used: 7189.344 cm⁻¹ (E″=142 cm⁻¹), 7189.541 cm⁻¹ (E″=1255 cm⁻¹), 7189.715 cm⁻¹ (E″=2005 cm⁻¹). Spectra were recorded using fast frequency scanning of a single distributed feedback (DFB) laser. A unique differential scheme for the recording of the absorption spectra was developed. An optimal technique for fitting the experimental spectra was developed.     

Nanosized IrO<Subscript>2</Subscript> electrocatalysts for oxygen evolution reaction in an SPE electrolyzer

Nanosized IrO₂ electrocatalysts (d ~ 7–9 nm) with specific surface area up to 100 m² g⁻¹ were synthesized and characterized for the oxygen evolution reaction in a solid polymer electrolyte (SPE) electrolyzer. The catalysts were prepared by a colloidal method in aqueous solution and a subsequent thermal treatment. An iridium hydroxide hydrate precursor was obtained at ~100 °C, which was, successively, calcined at different temperatures from 200 to 500 °C. The physico-chemical characterization was carried out by X-ray diffraction (XRD), thermogravimetry–differential scanning calorimetry (TG–DSC) and transmission electron microscopy (TEM). IrO₂ catalysts were sprayed onto a Nafion 115 membrane up to a loading of 3 mg cm⁻². A Pt catalyst was used at the cathode compartment with a loading of 0.6 mg cm⁻². The electrochemical activity for water electrolysis of the membrane-electrode assemblies (MEAs) was investigated in a single cell SPE electrolyzer by steady-state polarization curves, impedance spectroscopy and chrono-amperometric measurements. A maximum current density of 1.3 A cm⁻² was obtained at 1.8 V and 80 °C for the IrO₂ catalyst calcined at 400 °C for 1 h. A stable performance was recorded in single cell for this anode catalyst at 80 °C. The suitable catalytic activity and stability of the most performing catalyst were interpreted in terms of proper combination between nanostructure and suitable morphology.     

Fabrication of a nanoparticle TiO<Subscript>2</Subscript> photoelectrochemical cell utilizing a solid polymeric electrolyte of PAN–PC–LiClO<Subscript>4</Subscript>

A nanoparticle TiO₂ solid-state photoelectrochemical cell utilizing as a solid electrolyte of poly(acrylonitrile)–propylene–carbonate–lithium perchlorate (PAN–PC–LiClO₄) has been fabricated. The performance of the device has been tested in the dark and under illumination of 100-mW cm⁻² light. A nanoparticle TiO₂ film was deposited onto indium tin oxide-covered glass substrate by controlled hydrolysis technique assisted with spin-coating technique. The average grain size for the TiO₂ film is 76 nm. LiClO₄ salt was used as a redox couple. The room temperature conductivity of the electrolyte is 4.2 × 10⁻⁴ S cm⁻¹. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows the rectification property in the dark and shows the photovoltaic effect under illumination. The best J _sc and V _oc of the device were 2.82 μA cm⁻² and V _oc of 0.58 V, respectively, obtained at the conductivity of 4.2 × 10⁻⁴ S cm⁻¹ and intensity of 100 mW cm⁻². The J _sc was improved by about three times by introducing nanoparticle TiO₂ and by using a solid electrolyte of PAN–PC–LiClO₄ replacing PVC–PC–LiClO₄ in the device. The current transport mechanism of the cell is also presented in this paper.     

Detection of <Emphasis Type="Italic">trans</Emphasis>-isomers of hydrocarbon residues of lipid molecules by IR absorption

IR spectroscopy is used for a comparative analysis of the trans-isomerization of double bonds in hydrocarbon residuals of lactic and hydrogenated lipids. The maximum of the absorption band of the trans-isomers for all the lipid samples is found to lie at 965 cm⁻¹. An absorption band at 970 cm⁻¹ is discovered in the spectra of the lactic lipids near the analytic band of the trans-isomers at 965 cm⁻¹. Based on a gaussian approximation for their absorption spectral bands, the trans-isomer content in the lactic lipid samples is 10–11%. The absorption by lipid molecules at 970 cm⁻¹ has to be taken into account when determining the trans-isomer content of fat and oil products. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 138–142, January–February, 2009.     

Transmission spectra of epitaxial layers of Pb1 ? xEuxTe (0 ≤ x ≤ 0.37) solid solutions in the frequency range 7–4000 cm?1

The spectra of epitaxial Pb_{1 − x} Eu _x Te (0 ≤ x ≤ 0.37) solid solution layers grown on BaF₂ and Si substrates have been investigated over a wide frequency range 7–4000 cm⁻¹ at temperatures of 5–300 K. Apart from the phonon and impurity absorption lines, the absorption in a local mode in PbEuTe layers of substrates and buffer layers has been observed in the frequency range 110–114 cm⁻¹. As the temperature decreases from 300 to 5 K, the transverse phonon mode softens from 33.0 to 19.5 cm⁻¹.     

Tunable diode laser spectroscopy of benzene near 1684 nm with a low-temperature VCSEL

We describe the application of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) with extended tuning range to the detection of benzene vapor at atmospheric pressure. A benzene absorption feature centered at 1684.24 nm was accessed by reducing the heat sink temperature of a VCSEL designed for room-temperature operation to −55°C. This allowed us to increase the injection current and thus to extend a single-scan tuning interval up to 46.4 cm⁻¹ or 13.2 nm around a central wavelength of 1687.4 nm. Five absorption lines of methane in the 5903–5950 cm⁻¹ range could be acquired within single laser scans at a repetition rate of 500 Hz. A benzene absorption feature between 5926 and 5948 cm⁻¹ was recorded for concentration measurements at atmospheric pressure using a single-pass 1.2 m absorption cell. A 50 ppmv mixture of CH₄ in N₂ was introduced into the cell along with benzene vapor to calibrate benzene concentration measurements. Benzene mixing ratios down to ∼90 ppmv were measured using a direct absorption technique. The minimum detectable absorbance and detection limit of benzene were estimated to be ∼10⁻⁴ and 30 ppmv, respectively. Using the wavelength modulation technique, we measured a second harmonic sensor response to benzene vapor absorption in air at atmospheric pressure as a function of modulation index. We conclude that a low-temperature monolithic VCSEL operating near 1684 nm can be employed in compact benzene sensors with a detection limit in the sub-ppm range.     

Absorption line strengths of <Superscript>15</Superscript>NH<Subscript>3</Subscript> in the near infrared spectral region

We present initial results of an investigation of the near infrared absorption spectrum of ¹⁵NH₃ between 6468 and 6692 cm⁻¹. A widely tunable external cavity diode laser is used in a direct absorption setup to determine the line positions and line strengths of several lines in that spectral range. Line data measurements on a ¹⁴NH₃ sample are used for validation of the setup by comparison of the results with available literature data. The presented overview measurements on absorption lines of ¹⁵NH₃ have been performed to serve as a starting point for candidate line selection for prospective isotopic ratio measurements of ¹⁴NH₃ and ¹⁵NH₃.     

Sensitive detection of temperature behind reflected shock waves using wavelength modulation spectroscopy of CO2 near 2.7?μm

Tunable diode-laser absorption of CO₂ near 2.7 μm incorporating wavelength modulation spectroscopy with second-harmonic detection (WMS-2f) is used to provide a new sensor for sensitive and accurate measurement of the temperature behind reflected shock waves in a shock-tube. The temperature is inferred from the ratio of 2f signals for two selected absorption transitions, at 3633.08 and 3645.56 cm⁻¹, belonging to the ν ₁+ν ₃ combination vibrational band of CO₂ near 2.7 μm. The modulation depths of 0.078 and 0.063 cm⁻¹ are optimized for the target conditions of the shock-heated gases (P∼1–2 atm, T∼800–1600 K). The sensor is designed to achieve a high sensitivity to the temperature and a low sensitivity to cold boundary-layer effects and any changes in gas pressure or composition. The fixed-wavelength WMS-2f sensor is tested for temperature and CO₂ concentration measurements in a heated static cell (600–1200 K) and in non-reactive shock-tube experiments (900–1700 K) using CO₂–Ar mixtures. The relatively large CO₂ absorption strength near 2.7 μm and the use of a WMS-2f strategy minimizes noise and enables measurements with lower concentration, higher accuracy, better sensitivity and improved signal-to-noise ratio (SNR) relative to earlier work, using transitions in the 1.5 and 2.0 μm CO₂ combination bands. The standard deviation of the measured temperature histories behind reflected shock waves is less than 0.5%. The temperature sensor is also demonstrated in reactive shock-tube experiments of n-heptane oxidation. Seeding of relatively inert CO₂ in the initial fuel-oxidizer mixture is utilized to enable measurements of the pre-ignition temperature profiles. To our knowledge, this work represents the first application of wavelength modulation spectroscopy to this new class of diode lasers near 2.7 μm.     

Mid-infrared upconversion spectroscopy based on a Yb:fiber femtosecond laser

We present a system for molecular spectroscopy using a broadband mid-infrared laser with near-infrared detection. Difference frequency generation of a Yb:fiber femtosecond laser produced a mid-infrared (MIR) source tunable from 2100–3700 cm⁻¹ (2.7–4.7 μm) with average power up to 40 mW. The MIR spectrum was upconverted to near-infrared wavelengths for broadband detection using a two-dimensional dispersion imaging technique. Absorption measurements were performed over bandwidths of 240 cm⁻¹ (7.2 THz) with 0.048 cm⁻¹ (1.4 GHz) resolution, and absolute frequency scale uncertainty was better than 0.005 cm⁻¹ (150 MHz). The minimum detectable absorption coefficient per spectral element was determined to be 4.4×10⁻⁷ cm⁻¹ from measurements in low pressure CH₄, leading to a projected detection limit of 2 parts-per-billion of methane in pure nitrogen. In a natural atmospheric sample, the methane detection limit was found to be 30 parts-per-billion. The spectral range, resolution, and frequency accuracy of this system show promise for determination of trace concentrations in gas mixtures containing both narrow and broad overlapping spectral features, and we demonstrate this in measurements of air and solvent samples.     

Grafted natural rubber-based polymer electrolytes: ATR-FTIR and conductivity studies

Attenuated total reflectance–Fourier transformed infrared spectroscopy measurement is employed to study the interactions between the components of 30% methyl-grafted natural rubber (MG30), lithium trifluromethanesulfonate (LiCF₃SO₃ or LiTF), and propylene carbonate (PC). Vibrational spectra data of LiTF reveals that the ν_s(SO₃) at 1,045 cm⁻¹, δ_s(CF₃) at 777 cm⁻¹, and C=O stretching mode at 1,728 cm⁻¹ for MG30 have shifted to lower wave numbers in MG30–LiTF complexes indicating that complexation has occurred between MG30 and LiTF. The solvation of lithium ion is manifested in Li⁺ ← O=C interaction as shown by the downshifting and upshifting of C=O mode at 1,788 to 1,775 cm⁻¹ and ν_as(SO₃) at 1,250 to 1258 cm⁻¹, respectively, in LiTF–PC electrolytes. There is no experimental evidence of the interaction between MG30 and PC. Competition between MG30 and PC on associating with lithium ion is studied, and the studies show that the interaction between MG30–LiTF is stronger than that of the PC–LiTF in plasticized polymer–salt complexes. The effect of PC on the ionic conductivity of the MG30–LiTF system is explained in terms of the polymer, plasticizer, and salt interactions. The temperature dependence of conductivity of the polymer films obeys the Vogel–Tamman–Fulcher relation. Values of conductivity and activation energy of the MG30-based polymer electrolyte systems are presented and discussed.     

Analysis of trace impurities in semiconductor gas via cavity-enhanced direct frequency comb spectroscopy

Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) has demonstrated powerful potential for trace-gas detection based on its unique combination of high bandwidth, rapid data acquisition, high sensitivity, and high resolution, which is unavailable with conventional systems. However, previous demonstrations have been limited to proof-of-principle experiments or studies of fundamental laboratory science. Here, we present the development of CE-DFCS towards an industrial application—measuring impurities in arsine, an important process gas used in III–V semiconductor compound manufacturing. A strongly absorbing background gas with an extremely complex, congested, and broadband spectrum renders trace detection exceptionally difficult, but the capabilities of CE-DFCS overcome this challenge and make it possible to identify and quantify multiple spectral lines associated with water impurities. Further, frequency combs allow easy access to new spectral regions via efficient nonlinear optical processes. Here, we demonstrate detection of multiple potential impurities across 1.75–1.95 μm (5710–5130 cm⁻¹), with a single-channel detection sensitivity (simultaneously over 2000 channels) of ∼4×10⁻⁸ cm⁻¹ Hz^−1/2 in nitrogen and, specifically, an absorption sensitivity of ∼4×10⁻⁷ cm⁻¹ Hz^−1/2 for trace water doped in arsine.     

Conductivity studies of starch-based polymer electrolytes

A proton-conducting polymer electrolyte based on starch and ammonium nitrate (NH₄NO₃) has been prepared through solution casting method. Ionic conductivity for the system was conducted over a wide range of frequency between 50 Hz and 1 MHz and at temperatures between 303 K and 373 K. Impedance analysis shows that sample with 25 wt.% NH₄NO₃ has a smaller bulk resistance (R _b) compared to that of the pure sample. The amount of NH₄NO₃ was found to influence the proton conduction; the highest obtainable room temperature conductivity was 2.83 × 10⁻⁵ S cm⁻¹, while at 100 °C, the conductivity in found to be 2.09 × 10⁻⁴ S cm⁻¹. The dielectric analysis demonstrates a non-Debye behavior. Transport parameters of the samples were calculated using the Rice and Roth model and thus shows that the increase in conductivity is due to the increase in the number of mobile ions.     

Thin TiO2 grown by metal–organic chemical vapor deposition on (NH4)2S x -treated InP

The electrical characteristics of thin TiO₂ films prepared by metal–organic chemical vapor deposition grown on a p-type InP substrate were studied. For a TiO₂ film of 4.7 nm on InP without and with ammonium sulfide treatment, the leakage currents are 8.8×10⁻² and 1.1×10⁻⁴ A/cm² at +2 V bias and 1.6×10⁻¹ and 8.3×10⁻⁴ A/cm² at −2 V bias. The lower leakage currents of TiO₂ with ammonium sulfide treatment arise from the improvement of interface quality. The dielectric constant and effective oxide charge number density are 33 and 2.5×10¹³ cm², respectively. The lowest mid-gap interface state density is around 7.6×10¹¹ cm⁻² eV⁻¹. The equivalent oxide thickness is 0.52 nm. The breakdown electric field increases with decreasing thickness in the range of 2.5 to 7.6 nm and reaches 9.3 MV/cm at 2.5 nm.