Dependence of harmonic signals on sample-gas parameters in wavelength-modulation spectroscopy for precise absorption measurements

4 and N₂O, are given. Received: 4 March 1998/Revised version: 27 July 1998     

Rapid temperature tuning of a 1.4-mum diode laser with application to high-pressure H(2)O absorption spectroscopy

Enhanced wavelength tuning of a distributed-feedback InGaAsP diode laser is demonstrated by use of rapid temperature cycling. The laser-active region is cycled from -10 to +50 degrees C (scanning the output from 1399 to 1403 nm) at kilohertz rates by pulsed heating with an auxiliary 532-nm laser. Such 4-nm scans represent a ten-fold increase in the wavelength-scanning range offered by standard current-tuning techniques and thus extend the capabilities of scan-wavelength sensors and systems. As an example application, we demonstrate absorption spectroscopy of H(2)O vapor at a pressure of 10 atm.     

Ordering of hydrogen bonds in high-pressure low-temperature H2O

The near K-edge structure of oxygen in liquid water and ices III, II, and IX at 0.25 GPa and several low temperatures down to 4 K has been studied using inelastic x-ray scattering at 9884.7 eV with a total energy resolution of 305 and 175 meV. A marked decrease of the preedge intensity from the liquid phase and ice III to ices II and IX is attributed to ordering of the hydrogen bonds in the proton-ordered lattice of the latter phases. Density functional theory calculations including the influence of the Madelung potential of the ice IX crystal correctly account for the remaining preedge feature. Furthermore, we obtain spectroscopic evidence suggesting a possible new phase of ice at temperatures between 4 and 50 K.     

Modelling coal gasification in an entrained flow gasifier

Coal gasification processes in a slurry-feed-type entrained-flow gasifier are studied. Novel simulation methods as well as numerical results are presented. We use the vorticity-stream function method to study the characteristics of gas flow and a scalar potential function is introduced to model the mass source terms. The random trajectory model is employed to describe the behaviour of slurry-coal droplets. Very detailed results regarding the impact of the O₂/coal ratio on the distribution of velocity, temperature and concentration are obtained. Simulation results show that the methods are feasible and can be used to study a two-phase reacting flow efficiently.     

Methodology for temperature measurements in water vapor using wavelength-modulation tunable diode laser absorption spectrometry in the telecom C-band

A methodology based upon wavelength modulation and two-line thermometry for assessment of gas temperature by tunable diode laser absorption spectroscopy utilizing a standard tunable distributed feedback (DFB) diode laser working in the telecom C-band has been developed. Due to the high density of water lines in this wavelength region at elevated temperatures the methodology does not make use of two individual lines, but rather two groups of lines. The two groups identified have been found to have favorable properties for accurate temperature assessment in the 200–1000°C range, primarily a separation that is within a single DFB laser scan (∼20 GHz), an adequate linestrength, and sufficient difference in temperature dependence; the ratio of the peak values of the 2f-wm-signals, R, was found to increase monotonically with temperature, T, with a relative sensitivity, (ΔR/R)/(ΔT/T), above or around unity for most of the pertinent temperature range. The standard deviation of a temperature measurement with a 1 s integration time was found to be below 0.3%. It is shown that the temperature assessment has virtually no dependence on water concentration but a weak dependence on modulation amplitude.     

Diode-laser absorption measurements of CO2, H2O, N2O, and NH3 near 2.0 μm

2 , H₂O, N₂O, and NH₃ concentrations in various flowfields using absorption spectroscopy and extractive sampling techniques. An external-cavity diode laser with a tuning range of 1.953–2.057 μm was used to record absorption lineshapes from measured transitions in the CO₂ 4ν₂ ⁰+ν₃, ν₁+2ν₂ ⁰+ν₃, and 2ν₁+ν₃ bands, H₂O ν₂+ν₃and ν₁+ν₂ bands, N₂O 2ν₁+4ν₂ ⁰, ν₂ ¹+2ν₃, 3ν₁+2ν₂ ⁰, and 4ν₁ bands, and NH₃ν₁+ν₄ and ν₃+ν₄ bands. Measured CO₂, H₂O, and N₂O survey spectra were compared to calculations to verify the HITRAN96 database and used to determine optimum transitions for species detection. Individual lineshape measurements were used to determine fundamental spectroscopic parameters including the line strength, line-center frequency, and self-broadening coefficient of the probed transition. The results represent the first measurements of CO₂, H₂O, N₂O, and NH₃ absorption near 2.0 μm using room-temperature near-IR diode lasers. Received: 12 March 1998/Revised version: 7 May 1998     

Low temperature measurements by infrared spectroscopy in CoFe2O4 ceramic

This paper presents results of new far-infrared and middle-infrared measurements (wavenumber range of 4000?C100 cm^?1) of the CoFe₂O₄ ceramic in the temperature range from 300 K to 8 K. The band positions and their shapes remain constant across the wide temperature range. The quality of the sample was investigated by X-ray, EDS and EPMA studies. The CoFe₂O₄ retains the cubic structure (Fd - 3m) across the temperature range from 85 K to 360 K without any traces of distortion. Based on current knowledge the polycrystalline CoFe₂O₄ does not exhibit any phase transitions across the temperature range from 8 K to 300 K.     

Interest of absorption spectroscopy for the control of industrial processes. Application to H2 massive production

Absorption and TDLA spectroscopies find their applications in a lot of fields of research. The purpose of this article is to show how these methods can bring significant advances in chemical research projects. “H₂ massive production” using nuclear heat together with a thermochemical cycle is an important way to massively produce hydrogen, a potential energy vector. The sulfur–iodine cycle and the hybrid copper-chloride thermochemical cycles are some good candidates for water splitting.     

Computation of absorption by H2O near 4250 cm-1

By comparing computed and observed spectra over the region 4210–4310 cm^-1, it is shown that the H₂O line parameters calculated by Flaud and Camy-Peyret for this region represent a significant improvement over those listed in the revised version of the AFCRL Atmospheric Absorption Line Parameter Compilation.     

Applications of wavelength-modulation spectroscopy in resolution of pressure and modulation broadened spectra

Theoretical and experimental results for modulation absorption spectroscopy (with simultaneous amplitude and wavelength modulations) are given, with particular emphasis on the effects of pressure and modulation broadening. As expected, such broadening effects result in a loss of resolution of nearly overlapping lines, whether these are from one or more absorbing species. The effects of phase-sensitive detection at harmonics greater than the commonly used second are investigated. It is shown that when detection is performed at higher harmonics, one is able to counter the loss of resolution due to pressure and modulation broadening. Applications in measurements of congested spectra, and in the simultaneous measurement of more than one species, are discussed. Other general characteristics of signals obtained by using higher-harmonic detection are also discussed, together with corresponding applications.     

A difference in the electromagnetic properties of D2O and H2O ice revealed by resonance measurements

The dielectric parameters of H₂O and D₂O ice samples were studied by a resonance technique in the region of 6 GHz. The ratio of the resonance curve halfwidths at half maximum was measured for light and heavy ice in the temperature range from 0 to ?130°C. The temperature dependences of the resonance peak asymmetry of the two types of ice are qualitatively different. The ratio of the higher-frequency halfwidths at half maximum to the lower-frequency one plotted versus temperature exhibits a positive slope for light ice and a negative slope for heavy ice. It is suggested that the difference reflects the different quantum statistics of the hydrogen and deuterium nuclei in ice.     

Transesterification of an RNA model in buffer solutions in H2O and D2O

Transesterification of a phosphodiester bond of RNA models has been studied in various buffer solutions, under neutral and slightly alkaline conditions in H₂O and D₂O. The results show that imidazole is the only buffer system where a clear buffer catalysis on the cleavage of a phosphodiester bond is observed. The rate enhancement in sulphonic acid buffers is smaller, and a sulphonate base, particularly, is inactive as a catalyst. The rate‐enhancing effect of imidazole is, however, catalytic, and the catalytic inactivity of sulphonate buffers can be attributed to their structure and/or charge. The catalysis by imidazole is a complex system which, in addition to first‐order reactions, involves a process that shows a second‐order dependence in imidazole concentration. The latter reaction becomes significant in acidic imidazole buffers (pH < pK_a), as the buffer concentration increases. The kinetic solvent deuterium isotope effect k_H/k_D, referring to first‐order catalysis by imidazole base, is 2.3 ± 0.3. That referring to second‐order catalysis is most probably much larger, but an accurate value could not be obtained. Copyright © 2007 John Wiley & Sons, Ltd.     

Sensitive absorption measurements in the near-infrared region using off-axis integrated-cavity-output spectroscopy

A novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements of gas mixing ratios using near-infrared diode lasers and absorption-spectroscopy techniques. The instrument employs an off-axis trajectory of the laser beam through the cell to yield an effective optical path length of several kilometers without significant unwanted effects due to cavity resonances. As a result, a minimum detectable absorption of approximately 1.4×10^-5 over an effective optical path of 4.2 km was obtained in a 1.1-Hz detection bandwidth to yield a detection sensitivity of approximately 3.1×10^-11 cm^-1 Hz^-1/2. The instrument has been used for sensitive measurements of CO, CH₄, C₂H₂ and NH₃. Received: 6 May 2002 / Revised version: 31 May 2002 / Published online: 2 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-650/965-7074, E-mail: d.baer@lgrinc.com     

Search for anomalous effects in H2O/D2O mixtures by neutron total cross section measurements

We investigate anomalies ascribed to quantum entanglement phenomena recently reported in deep inelastc neutron scattering (DINS) measurements by an independent neutron technique on H(2)O/D(2)O mixtures. We performed transmission experiments to study several liquid H(2)O/D(2)O mixtures at room temperature in the epithermal energy range. We obtain the total cross sections of the mixtures, which are in agreement with the expected results according to the tabulated values within a 0.3% relative error. We observe no anomalies and stress the limitations of the validity of the data-processing procedures employed in the DINS experiments where the anomalies were reported.     

A high efficiency NH3/H2O absorption power cycle

A work producing cycle has been developed showing a thermodynamic efficiency considerably higher than that of the Rankine cycle. The new cycle employs a mixture of H₂O and NH₃ as the working fluid and uses an absorption process similar to that of absorption refrigerators. Its advantage over existing power cycles working with the same mixture (i.e. the Kalina cycle) is simplicity as far as devices, construction, operation and maintenance are concerned. For the detailed calculation of the proposed cycle a method has been developed, which employs analytical functions describing the thermodynamic properties of the NH₃/H₂O mixture. The proposed cycle has been compared with Rankine cycles working at the same temperature levels. For fixed upper (i.e. superheating) and lower (i.e. condensation) temperatures, the new cycle shows an efficiency 20% higher than that of the Rankine cycle if the boiling temperature is high, while for low boiling temperatures the superiority of the proposed cycle is much more pronounced. A parametric study has also been conducted for the new cycle, wwhich showed, inter alia, that the optimum difference between the mass fractions of the rich and weak solution is about 0.1 kg NH₃/kg mixture.     

Water enrichment by H2O ortho-isomer: Four-photon and NMR spectroscopy

Ratio of H₂O ortho-/para-spin-isomers in water of different treatment procedures (distilled or cavitation fountain) were studied by both Rayleigh wing four-photon spectroscopy and ¹H nuclear magnetic resonance (NMR) spectroscopy. Low-frequency gas-like rotational resonances were observed in the 0.1–1.5 cm^?1 (3–45 GHz) spectral range and NMR proton density was measured in both water samples. We established that the intensity of ortho-isomer line (6₁₆?5₂₃)0.74 cm^?1 measured by four-photon spectroscopy increases by factor of ～3.5 after cavitation treatment of distilled water. Moreover, the proton density measured by NMR spectroscopy in the same sample grows on ～17%. We have suggested that the enrichment of the distilled water by ortho-H₂O molecules was achieved due to cavitation bubbles collapse when the water passes through the supercritical state.