Shock-tube study of high-pressure H2O spectroscopy

Water-vapor absorption features near 7117, 7185, and 7462 cm(-1) were probed at pressures to 65 atm (1 atm = 760 Torr) and temperatures to 1800 K in shock-heated mixtures of H(2)O in N(2) and Ar with a diode-laser source. Calculated absorbances based on Voigt line shapes and measured line parameters were in good agreement, within 10%, with measured absorbances at 7185.4 and 7117.4 cm(-1). We obtained temperature-dependent N(2) and Ar shift parameters for H(2)O absorption features by shifting the calculated spectra to match the recorded absorption scan. Absorbance simulations based on line parameters from HITRAN and HITEMP were found to be similar over the range of temperatures 600-1800 K and were within 25% of the measurements. The combined use of Toth's [Appl. Opt. 36, 4851 (1994)] line positions and strengths and HITRAN broadening parameters resulted in calculated absorption coefficients that were within 15% of the measurements at all three probed wavelengths.     

High-precision laser spectroscopy D/H and 18O/16O measurements of microliter natural water samples

Newly available gas analyzers based on off-axis integrated cavity output spectroscopy (OA-ICOS) lasers have been advocated as an alternative to conventional isotope-ratio mass spectrometers (IRMS) for the stable isotopic analysis of water samples. In the case of H2O, OA-ICOS is attractive because it has comparatively low capital and maintenance costs, the instrument is small and field laboratory portable, and provides simultaneous D/H and 16O/18O ratio measurements directly on H2O molecules with no conversion of H2O to H2, CO, or H2/CO2-water equilibration required. Here we present a detailed assessment of the performance of a liquid-water isotope analyzer, including instrument precision, estimates of sample memory and sample mass effects, and instrumental drift. We provide a recommended analysis procedure to achieve optimum results using OA-ICOS. Our results show that, by using a systematic sample analysis and data normalization procedure routine, measurement accuracies of +/-0.8 per thousand for deltaD and +/-0.1 per thousand delta18O are achievable on nanoliter water samples. This is equivalent or better than current IRMS-based methods and at a comparable sample throughput rate.     

Determination of H2O and CO2 concentrations in fluid inclusions in minerals using laser decrepitation and capacitance manometer analysis

Water and carbon dioxide concentrations within individual and selected groups of fluid inclusions in quartz were analyzed by using laser decrepitation and quantitative capacitance manometer determination. The useful limit of detection (calculated as ten times the typical background level) is about 5 x 10(-10) mol of H2O and 5 x 10(-11) mol of CO2; this H2O content translates into an aqueous fluid inclusion approximately 25 micrometers in diameter. CO2/H2O determinations for 38 samples (100 separate measurements) have a range of H2O amounts of 5.119 x 10(-9) to 1.261 x 10(-7) mol; CO2 amounts of 7.216 x 10(-10) to 1.488 x 10(-8) mol, and CO2/H2O mole ratios of 0.011 to 1.241. Replicate mole ratio determinations of CO2/H2O for three identical (?) clusters of inclusions in quartz have average mole ratios of 0.0305 +/- 0.0041 1 sigma. Our method offers much promise for analysis of individual fluid inclusions, is sensitive, is selective when the laser energy is not so great as to melt the mineral (laser pits approximately 50 micrometers in diameter), and permits rapid analysis (approximately 1 h per sample analysis).     

Precision trace gas analysis by FT-IR spectroscopy. 2. The 13C/12C isotope ratio of CO2

We report the development of a method of carbon stable isotope ratio analysis based on 1-cm-1 resolution Fourier transform infrared (FT-IR) spectroscopy, deployable in both laboratory and field applications. We demonstrate the determination of the 13C/12C ratio of CO2 (i.e., delta 13CO2) in air with an analytical precision of the order of +/- 0.1/1000 (i.e., +/- 0.01%). The FT-IR method relies on calibration using synthetically calculated absorbance spectra and a multivariate calibration algorithm. The method requires no sample preparation other than optional drying of the sample and may be applied directly to ambient air samples containing approximately 350 mumol mol-1 CO2 (molar mixing ratio). It may also be applied to samples more concentrated in CO2, such as human breath, approximately 5% CO2. We demonstrate the utility of the technique to the analysis of delta 13CO2 in air during an experimental field campaign and to the laboratory-based analysis of human breath. A similar method could also be used to determine the H/D ratio in atmospheric water vapor.     

Absorption of 9.6-micron CO2 laser radiation by CO2 at elevated temperatures

Absorption of 9.6-micron CO2 laser radiation by CO2 at temperatures between 296 and 625 K has been measured at a pressure of 200 Torr. Experimental results for the R1O-R26 and P1O-P28 transitions have been obtained and compared with computed values of absorption. The relative optical broadening coefficients due to He and N2 have been measured on the R16-R22 and P16-P22 transitions over the same temperature range.     

In Situ Combustion Measurements of CO(2) by Use of a Distributed-Feedback Diode-Laser Sensor Near 2.0 mum

High-resolution absorption measurements of CO(2) were made in a heated static cell and in the combustion region above a flat-flame burner for the development of an in situ CO(2) combustion diagnostic based on a distributed-feedback diode laser operating near 2.0 mum. Calculated absorption spectra of high-temperature H(2)O and CO(2) were used to find candidate transitions for CO(2) detection, and the R(50) transition at 1.997 mum (the nu(1) + 2nu(2) + nu(3) band) was selected on the basis of its line strength and its isolation from interfering high-temperature water absorption. Measurements of spectroscopic parameters such as the line strength, the self-broadening coefficient, and the line position were made for the R(50) transition, and an improved value for the line strength is reported. The combustion-product populations of CO(2) in the combustion region above a flat-flame burner were determined in situ to verify the measured spectroscopic parameters and to demonstrate the feasibility of the diode-laser sensor.     

Photoacoustic distributed feedback laser spectroscopy on hydrogen fluoride

We have developed a photoacoustic spectrometer based on a distributed feedback (DFB) diode laser. The single-mode emission of the laser can be tuned continuously over 700 GHz enabling the precise determination of absorption line parameters. Our experiments were performed on the rotational lines P2 and P3 of the vibrational transition 2-0 (overtone) of hydrogen fluoride (HF) at 1304.534 nm and 1312.591 nm (vacuum), respectively. The pressure broadening coefficient due to elastic collisions with N(2) molecules is found to be 5.92 +/- 0.04 GHz/atm (296 K) and 5.38 +/- 0.04 GHz/atm, respectively. The Doppler linewidths turn out to be 630 +/- 40 MHz and 670 +/- 40 MHz (296 K), respectively. The pressure-induced line shifts of the absorption lines for N(2) are 540 +/- 40 MHz/ atm and 580 +/- 40 MHz/atm, respectively.     

Rapid, online quantification of H2S in JP-8 fuel reformate using near-infrared cavity-enhanced laser absorption spectroscopy

One of the key challenges in reforming military fuels for use with fuel cells is their high sulfur content, which can poison the fuel cell anodes. Sulfur-tolerant fuel reformers can convert this sulfur into H(2)S and then use a desulfurizing bed to remove it prior to the fuel cell. In order to optimize and verify this desulfurization process, a gas-phase sulfur analyzer is required to measure H(2)S at low concentrations (<1 ppm(v)) in the presence of other reforming gases (e.g., 25-30% H(2), 10-15% H(2)O, 15% CO, 5% CO(2), 35-40% N(2), and trace amounts of light hydrocarbons). In this work, we utilize near-infrared cavity-enhanced optical absorption spectroscopy (off-axis ICOS) to quantify H(2)S in a JP-8 fuel reformer product stream. The sensor provides rapid (2 s), highly precise (±0.1 ppm(v)) measurements of H(2)S in reformate gases over a wide dynamic range (0-1000 ppm(v)) with a low detection limit (3σ = ±0.09 ppm(v) in 1 s) and minimal cross-interferences from other present species. It simultaneously quantifies CO(2) (±0.2%), CH(4) (±150 ppm(v)), C(2)H(4) (±30 ppm(v)), and H(2)O (±300 ppm(v)) in the reformed gas for a better characterization of the fuel reforming process. Other potential applications of this technology include measurement of coal syngas and H(2)S in natural gas. By including additional near-infrared, distributive feedback diode lasers, the instrument can also be extended to other reformate species, including CO and H(2).     

Ametryn degradation in the ultraviolet (UV) irradiation/hydrogen peroxide (H2O2) treatment

Ultraviolet (UV) irradiation (253.7nm) in the presence of hydrogen peroxide (H(2)O(2)) was used to decompose aqueous ametryn. The concentrations of ametryn were measured with time under various experiment conditions. The investigated factors included H(2)O(2) dosages, initial pH, initial ametryn concentrations, and a variety of inorganic anions. Results showed that ametryn degradation in UV/H(2)O(2) process was a pseudo-first-order reaction. Removal rates of ametryn were greatly affected by H(2)O(2) dosage and initial concentrations of ametryn, but appeared to be slightly influenced by initial pH. Furthermore, we investigated the effects of four anions (SO(4)(2-), Cl(-), HCO(3)(-), and CO(3)(2-)) on ametryn degradation by UV/H(2)O(2). The impact of SO(4)(2-) seemed to be insignificant; however, Cl(-), HCO(3)(-), and CO(3)(2-) considerably slowed down the degradation rate because they could strongly scavenge hydroxyl radicals (OH) produced during the UV/H(2)O(2) process. Finally, a preliminary cost analysis revealed that UV/H(2)O(2) process was more cost-effective than the UV alone in removal of ametryn from water.     

Diode-laser absorption technique for simultaneous measurements of multiple gasdynamic parameters in high-speed flows containing water vapor

A distributed-feedback InGaAsP diode laser, emitting near 1.38 μm, was used to acquire spectrally resolved absorption profiles of H(2)O lines in the ν(1) + ν(3) band at a repetition rate of 10 kHz. The profiles were used for simultaneous measurements of flow parameters in high-speed, one-dimensional (1-D) transient flows generated in a shock tube. Velocity was determined from the Doppler shift, which was measured with a pair of profiles simultaneously acquired at different angles with respect to the flow direction. Temperature was determined from the intensity ratio of two adjacent lines. Pressure and density were found from the fractional absorption. From these primary gasdynamic variables, the mass and momentum fluxes were determined. Experiments were conducted with three different gas mixtures in the shock tube: pure H(2)O at initial pressures lower than 3 Torr, up to 6% of H(2)O in O(2) at initial pressures below 120 Torr, and up to 8% of H(2)O in O(2) at initial pressures below 35 Torr. In the third case, pyrolysis of H(2) /O(2) behind incident shocks produced known yields of H(2)O. With all three mixtures, results compare well with 1-D shock calculations. This H(2)O diagnostic strategy shows promise for applications in both ground and flight testing.     

Measurements of collisional broadening coefficients by infrared polarization spectroscopy

We present measurements of collisional broadening coefficients, obtained at atmospheric pressure, by polarization spectroscopy. Using tunable single mode laser radiation at approximately 2 microm, high-resolution infrared polarization spectra were recorded for CO2-Ar and CO2-He binary mixtures. The recorded polarization spectra were fitted with a Lorentzian cubed function form to obtain the broadening coefficients. The full-width at half-maxima (FWHM) collisional broadening rates of CO2 by Ar and He, for the R14 (12 degrees1<--00 degrees0) line, have been determined to be 0.161+/-0.018 cm-1 atm-1 and 0.1823+/-0.0032 cm-1 atm-1, respectively.     

Diode-Laser Absorption Measurements of CO(2) Near 2.0 mum at Elevated Temperatures

A diode-laser sensor system based on absorption spectroscopy techniques has been developed for nonintrusive measurements of CO(2) in high-temperature environments. Survey spectra of the CO(2) (20 degrees 1,04 degrees 1)(I)-00 degrees 0 and (20 degrees 1,04 degrees 1)(II)-00 degrees 0 bands between 1.966 and 2.035 mum (4915-5085 cm(-1)) were recorded at temperatures between 296 and 1425 K in a heated static cell and compared with calculated spectra (by using the HITRAN 96/HITEMP database) to find candidate transitions for CO(2) detection. High-resolution measurements of the CO(2) R(56) line shape [(20 degrees 1,04 degrees 1)(II)-00 degrees 0 band] were used to determine the transition line strength, the self-broadening half-width, and the coefficient of temperature dependence of the self-broadening half-width. The results represent what are believed to be the first measurements of CO(2) absorption near 2.0 mum with room-temperature diode lasers. Potential applications of the diode-laser sensor system include in situ combustion measurements and environmental monitoring.     

Probing hot electron flow generated on Pt nanoparticles with Au/TiO2 Schottky diodes during catalytic CO oxidation

Hot electron flow generated on colloid platinum nanoparticles during exothermic catalytic carbon monoxide oxidation was directly detected with Au/TiO2 diodes. Although Au/TiO2 diodes are not catalytically active, platinum nanoparticles on Au/TiO2 exhibit both chemicurrent and catalytic turnover rate. Hot electrons are generated on the surface of the metal nanoparticles and go over the Schottky energy barrier between Au and TiO2. The continuous Au layer ensures that the metal nanoparticles are electrically connected to the device. The overall thickness of the metal assembly (nanoparticles and Au thin film) is comparable to the mean free path of hot electrons, resulting in ballistic transport through the metal. The chemicurrent and chemical reactivity of nanoparticles with citrate, hexadecylamine, hexadecylthiol, and TTAB (tetradecyltrimethylammonium bromide) capping agents were measured during catalytic CO oxidation at pressures of 100 Torr O2 and 40 Torr CO at 373-513 K. We found that chemicurrent yield varies with each capping agent but always decreases with increasing temperature. We suggest that this inverse temperature dependence is associated with the influence of charging effects due to the organic capping layer during hot electron transport through the metal-oxide interface.     

Analysis of aircraft exhausts with Fourier-transform infrared emission spectroscopy

Because of the worldwide growth in air traffic and its increasing effects on the atmospheric environment, it is necessary to quantify the direct aircraft emissions at all altitudes. In this study Fourier-transform infrared emission spectroscopy as a remote-sensing multi-component-analyzing technique for aircraft exhausts was investigated at ground level with a double pendulum interferometer and a line-by-line computer algorithm that was applied to a multilayer radiative transfer problem. Initial measurements were made to specify the spectral windows for traceable compounds, to test the sensitivity of the system, and to develop calibration and continuum handling procedures. To obtain information about the radial temperature and concentration profiles, we developed an algorithm for the analysis of an axial-symmetric multilayered plume by use of the CO(2) hot band at approximately 2400 cm(-1). Measurements were made with several in-service engines. Effects that were due to engine aging were detected but have to be analyzed systematically in the near future. Validation measurements were carried out with a conventional propane gas burner to compare the results with those obtained with standard measurement equipment. These measurements showed good agreement to within +/-20% for the CO and NO(x) results. The overall accuracy of the system was found to be +/-30%. The detection limits of the system for a typical engine plume (380 degrees C, ? = 50 cm) are below 0.1% for CO(2), ~0.7% for H(2)O, ~20 ppmv (parts per million by volume) for CO, and ~90 ppmv for NO.     

High-accuracy gas analysis via isotope dilution mass spectrometry: carbon dioxide in air

An absolute method, based on isotope dilution mass spectrometry, is described for the determination of atmospheric concentrations of carbon dioxide (CO2) in dry air. In this study, the relative amounts of sample and spike gases are measured manometrically under temperature control before blending. The spike CO2 composition is approximately 0.1 atom % 13C while the oxygen isotopic composition is "normal". Exhaustive assessment of potential error sources leads to accountability of observed imprecision and determination of accuracy confidence intervals (CI). The imprecision interval (95% CI) about the mean is smaller than +/- 0.1% (+/- 0.4 mumol/mol) while the accuracy interval (95% CI) is +/- 0.15% (+/- 0.52 mumol/mol) for air having a CO2 concentration of about 350 mumol/mol. Calculated concentrations of CO2 are statistically indistinguishable from those generated by gravimetry, an independent method of analysis. In this study, the major contributors to uncertainty and imprecision are the predetermination of the gas volume ratio and the measurement of the isotopic composition of the blended CO2, respectively.     

CO-sensing properties of In/sub 2/O/sub 3/-doped SnO/sub 2/ thick-film sensors: effect of doping concentration and grain size

In/sub 2/O/sub 3/-doped SnO/sub 2/ nanoparticles were prepared using sol-gel technique from 0.1-M solutions of both stannic chloride (SnCl/sub 4/ 5H/sub 2/O) and indium nitrate. The doping concentration was varied from 7.718/spl times/10/sup -5/ to 3.859/spl times/10/sup -4/ moles. The average particle size, as measured from XRD, SEM, and TEM analyses, varies from 34-130 nm as a result of powder calcination at different temperatures ranging from 300/spl deg/C-900/spl deg/C. Thick-film samples with a thickness of /spl sim/15 /spl mu/m, were tested for low concentration (15-1000 ppm) of CO in air ambient. The optimal temperature for CO sensing is found to be 220/spl deg/C-240/spl deg/C. A blue shift in the sensing temperature and increase in sensitivity factor (S/sub f/) is observed with increasing doping concentration of indium oxide. Maximum sensitivity factor of /spl sim/5 is found for the highest doping concentration (3.859/spl times/10/sup -4/ moles) at 1000 ppm of CO concentration. The morphological and elemental studies of the film are carried out using SEM, TEM, XRD, and EDAX techniques. The results are discussed based on elemental analyses and available theories.     

Photodegradation of 17beta-estradiol in water by UV-vis/Fe(III)/H2O2 system

Photodegradation of 17beta-estradiol (E2) in aqueous solutions by UV-vis/Fe(III)/H(2)O(2) system, namely Photo-Fenton system, was preliminarily investigated under a 250 W metal halide lamp (lambda > or = 313 nm). The influences of initial pH value, initial concentration of H(2)O(2) and E2 on photodegradation efficiency of E2 were discussed and the amount of CO(2) produced by the photodegradation reaction was measured. The results indicates that E2 could be decomposed efficiently in UV-vis/Fe(III)/H(2)O(2) system. Under the condition of 10.0 micromol L(-1) Fe(III), 1000 micromol L(-1) H(2)O(2) and pH 3.0, the degradation efficiency of 18.4 micromol L(-1) E2 reach 75.2% after the irradiation of 160 min. Over the range of pH 3.0-6.0, the higher acidity, the higher the degradation efficiency of E2 and initial reaction rate are. The degradation efficiency of E2 increases with increasing of initial concentration of H(2)O(2) and with decreasing of initial concentration of E2. The E2 mineralization efficiency increases with reaction time but the mineralization efficiency was lower. When the initial concentration of Fe(III) and H(2)O(2) were 10.0 and 1000 micromol L(-1), respectively, the mineralization efficiency of 18.4 micromol L(-1) E2 solution with pH 3.0 was only 21.6% after 160 min irradiation. It is suggested that the mineralization occurred probably only at aromatic ring.     

Pulsed laser photofragment emission for detection of mercuric chloride

The viability of pulsed laser photofragment emission (PFE) is evaluated for the in situ measurement of vapor-phase mercuric chloride (HgCl(2)) concentration in combustion flue gas. Dispersed emissions from both the Hg (6(3)P(1)) and HgCl (B(2)Sigma(+)) photoproducts are presented, and the dependence of the HgCl(2) PFE signal originating from Hg (6(3)P(1)) on the collisional environment is examined for buffer-gas mixtures of N(2), O(2), and CO(2). Integrated PFE intensity measurements as a function of buffer gas pressure support the assumption that the primary effect of the relevant flue gas constituents is to quench emission from Hg (6(3)P(1)). The quenching rate constants for PFE from HgCl(2) were measured to be 1.37 (+/-0.16) x 10(5) Torr(-1) s(-1) for N(2), 9.35 (+/-0.25) x 10(6) Torr(-1) s(-1) for O(2), and 1.49 (+/-0.29) x 10(6) Torr(-1) s(-1) for CO(2). These values are in good accord with literature values for the quenching of Hg (6(3)P(1)). The emission cross section for Hg (6(3)P(1)) generated by photodissociation of HgCl(2) in 760 Torr N(2) is found to be 1.0 (+/-0.2) x 10(-25) m(2) by comparing the PFE signal to N(2) Raman scattering.     

Atomic layer deposition of SiO2 thin films using tetrakis(ethylamino)silane and ozone

We examined the atomic layer deposition (ALD) of silicon dioxide thin films on a silicon wafer by alternating exposures to tetrakis(ethylamino)silane [Si(NHC2H5)4] and O3. The growth kinetics of silicon oxide films was examined at substrate temperatures ranging from 325 to 514 degrees C. The deposition was governed by a self-limiting surface reaction, and the growth rate at 478 degrees C was saturated at 0.17 nm/cycle for Si(NHC2H5)4 exposures of 2 x 10(6) L (1 L = 10(-6) Torr x s). The films deposited at 365-404 degrees C exhibited a higher deposition rate of 0.20-0.21 nm/cycle. However, they contained impurities, such as carbon and nitrogen, and showed poor film qualities. The concentration of impurities decreased with increasing substrate temperature. It was found that the films deposited in the high-temperature regime (478-514 degrees C) showed excellent physical and electrical properties equivalent to those of LPCVD films.     

One-dimensional TiO2 nanomaterials: preparation and catalytic applications

This work reports on the syntheses of one-dimensional (1D) H2Ti3O7 materials (nanotubes, nanowires and their mixtures) by autoclaving anatase titania (Raw-TiO2) in NaOH-containing ethanol-water solutions, followed by washing with acid solution. The synthesized nanosized materials were characterized using XRD, TEM/HRTEM, BET and TG techniques. The autoclaving temperature (120-180 degrees C) and ethanol-to-water ratio (V(EtOH)/V(H2O) = 0/60 approximately 30/30) were shown to be critical to the morphology of H2Ti3O7 product. The obtained H2Ti3O7 nanostructures were calcined at 400-900 degrees C to prepare 1D-TiO2 nanomaterials. H2Ti3O7 nanotubes were converted to anatase nanorods while H2Ti3O7 nanowires to TiO2(B) nanowires after the calcination at 400 degrees C. The calcination at higher temperatures led to gradual decomposition of the wires to rods and phase transformation from TiO2(B) to anatase then to rutile. Photocatalytic degradation of methyl orange was conducted to compare the photocatalytic activity of these 1D materials. These 1D materials were used as new support to prepare Au/TiO2 catalysts for CO oxidation at 0 degrees C and 1,3-butadiene hydrogenation at 120 degrees C. For the CO oxidation reaction, Au particles supported on anatase nanorods derived from the H2Ti3O7 nanotubes (Au/W-180-400) were 1.6 times active that in Au/P25-TiO2, 4 times that in Au/Raw-TiO2, and 8 times that on TiO2(B) nanowires derived from the H2Ti3O7 nanotubes (Au/M-180-400). For the hydrogenation of 1,3-butadiene, however, the activity of Au particles in Au/M-180-400 was 3 times higher than those in Au/W-180-400 but similar to those in Au/P25-TiO2. These results demonstrate that the potential of 1D-TiO2 nanomaterials in catalysis is versatile.