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A novel method has been implemented for measuring the concentration of gas species, water vapor and carbon dioxide, within a narrow channel flow field non-invasively using tunable diode laser absorption spectroscopy (TDLAS) in conjunction with a laser modulated at a high frequency (Wavelength Modulation Spectroscopy (WMS)) tuned to the ro-vibrational transition of the species. This technique measures the absorption profile which is a strong function of the species concentration across short path lengths and small time spans, as in PEM fuel cells during high load cycles. This method has been verified in a transparent circular flow 12 cm path length and a 12 mm rectangular flow channel. Distinct absorption peaks for water vapor and carbon dioxide have been identified, and concentrations of water vapor and carbon dioxide within the test cells have been measured in situ with high temporal resolutions. A comparison of the full width at half maximum (FWHM) of the absorption lineshapes to the partial pressure of water vapor and carbon dioxide showed a predominantly linear relationship, except in the lower partial pressure regions. Test section temperature was observed to have very minimal impact on these curves at low partial pressure values. A porous media like a membrane electrode assembly (MEA) similar to those used in PEM fuel cells sandwiched between two rectangular flow channels was also tested. Some of the scattered radiation off the MEA was observed using a photodiode at high gain, allowing for more localized species detection. The technique was used to monitor the humidity on either side of the MEA during both temperature controlled and super-saturated conditions. The measurements were observed to be repeatable to within 10 %.
Gas phase molecular spectroscopy is a powerful tool for obtaining information on the geometry and internal structure of isolated molecules as well as on the interactions that they undergo. It enables the study of fundamental parameters and processes and is also used for the sounding of gas media through optical techniques. It has been facing always renewed challenges, due to the considerable improvement of experimental techniques and the increasing demand for accuracy and scope of remote sensing applications. In practice, the radiating molecule is usually not isolated but diluted in a mixture at significant total pressure. The collisions among the molecules composing the gas can have a large influence on the spectral shape, affecting all wavelength regions through various mechanisms. These must be taken into account for the correct analysis and prediction of the resulting spectra. This book reviews our current experimental and theoretical knowledge and the practical consequences of collisional effects on molecular spectral shapes in neutral gases. General expressions are first given. They are formal of difficult use for practical calculations often but enable discussion of the approximations leading to simplified situations. The first case examined is that of isolated transitions, with the usual pressure broadening and shifting but also refined effects due to speed dependence and collision-induced velocity changes. Collisional line-mixing, which invalidates the notion of isolated transitions and has spectral consequences when lines are closely spaced, is then discussed within the impact approximation. Regions where the contributions of many distant lines overlap, such as troughs between transitions and band wings, are considered next. For a description of these far wings the finite duration of collisions and concomitant breakdown of the impact approximation must be taken into account. Finally, for long paths or elevated pressures, the dipole or polarizability induced by intermolecular interactions can make significant contributions. Specific models for the description of these collision induced absorption and light scattering processes are presented. The above mentioned topics are reviewed and discussed from a threefold point of view: the various models, the available data, and the consequences for applications including heat transfer, remote sensing and optical sounding. The extensive bibliography and discussion of some remaining problems complete the text. - State-of-the-art on the subject - A bibliography of nearly 1,000 references - Tools for practical calculations - Consequences for other scientific fields - Numerous illustrative examples - Fulfilling a need since there is no equivalent monograph on the subject
Line by line calculations of absorption spectra were carried out for the 2.0 and the 2.7 micron bands of carbon dioxide and for the 2.7 micron band of water vapor. The parameters for these calculations are taken from published listings for these bands. The calculations are compared with experimental data of the same spectral resolution, this being a fraction of a wavenumber. The comparisons show the line positions to be in good agreement with the experimental data. The 2.0 micron bands of carbon dioxide differ from the calculations by a small amount, but adjustment of parameters is required for the experimental and calculated values to agree in the 2.7 micron bands of carbon dioxide. There are large differences between calculated and experimental spectra in the 2.7 micron band of water vapor throughout much of the spectra. (Author).
This thesis presents a highly innovative study of the ultrafast structural and vibrational dynamics of hydrated phospholipids, the basic constituents of cell membranes. As a novel approach to the water-phospholipid interface, the author studies phosphate vibrations using the most advanced methods of nonlinear vibrational spectroscopy, including femtosecond two-dimensional infrared spectroscopy. He shows for the first time that the structure of interfacial water undergoes very limited fluctuations on a 300 fs time scale and that the lifetimes of hydrogen bonds with the phospholipid are typically longer than 10 ps. Such properties originate from the steric hindrance of water fluctuations at the interface and the orienting action of strong electric fields from the phospholipid head group dipoles. In an extensive series of additional experiments, the vibrational lifetimes of the different vibrations and the processes of energy dissipation are elucidated in detail.
The theoretical basis and computational procedures for producing absorption spectra of water vapor and carbon dioxide under varying conditions of temperature and pressure are discussed. Such spectra are produced with a line- by-line analysis using theoretically calculated spectral parameters. Any experimentally practical degree of spectral resolution is possible. (Author).
Explores the latest advances and applications of specialty and electronic gas analysis The semiconductor industry depends upon a broad range of instrumental techniques in order to detect and analyze impurities that may be present in specialty and electronic gases, including permanent gases, water vapor, reaction by-products, and metal species. Trace Analysis of Specialty and Electronic Gases draws together all the latest advances in analytical chemistry, providing researchers with both the theory and the operating principles of the full spectrum of instrumental techniques available for specialty and electronic gas analysis. Moreover, the book details the advantages and disadvantages of each technique, steering readers away from common pitfalls. Featuring contributions from leading analytical and industrial chemists, Trace Analysis of Specialty and Electronic Gases covers a wide range of practical industrial applications. The book begins with the historical development of gas analysis and then focuses on particular subjects or techniques such as: Metals sampling and ICP-MS analysis Improvements in FTIR spectroscopy Water vapor analysis techniques New infrared laser absorption spectroscopy approaches GC/MS, GC/AED, and GC-ICP-MS techniques Gas chromatography columns Atmospheric pressure ionization mass spectrometry Lastly, the book examines gas mixtures and standards that are critical for instrument calibration. There are also two appendices offering information on fittings and material compatibility. With its thorough review of the literature and step-by-step guidance, Trace Analysis of Specialty and Electronic Gases enables researchers to take full advantage of the latest advances in gas analysis. Although the book's focus is the semiconductor and electronics industry, analytical chemists in other industries facing challenges with such issues as detection selectivity and sensitivity, matrix gas interference, and materials compatibility will also discover plenty of useful analytical approaches and techniques.