Infrared spectroscopy, long-path

DeKlein cam, McTaggaet IP, Smith KA, Stevens RJ, Harrison R and Laughlin RJ (1999) Measurement of nitrous oxide emissions from grassland soil using photo-acoustic infrared spectroscopy, long-path infrared spectroscopy, gas chromatography, and continuous flow isotope-ratio mass spectrometry. Commun Soil Sci Plant Analysis 30 1463-1477. 

McAfee, J. M., J. N. Pitts. Jr., and A. M. Winer. In-situ Long-path Infrared Spectroscopy of Photochemical Air Pollutants in an Environmental Chamber. Paper No. 125 Presented at the Pacific Conference on Chemistry and Spectroscopy, San Francisco, California, October 16-18, 1974. (American Chemical Society—lOth Western Regional Meeting and Society for Applied Spectroscopy—13th Pacific Meeting)... 

Tuazon, E. C., A. M. Winer, and J. N. Pitts, Jr., Trace Pollutant Concentrations in a Multiday Smog Episode in the California South Coast Air Basin by Long Path Length Fourier Transform Infrared Spectroscopy, Environ. Sci. Technol., 15, 1232-1237 (1981). 

Shortly after the discovery of photochemical air pollution, Stephens and his co-workers (Stephens et al., 1956 Stephens, 1987) applied long-path infrared spectroscopy to identifying and measuring products in the photooxidation of organic-NO, mixtures. In the photooxidations of 3-methylheptane and, to a larger extent, 2,3-butanedione, a set of infrared bands that could not be assigned to known products was observed. These were assigned to a previously unobserved species, which was initially called compound X. It was ultimately shown to be peroxyacetyl nitrate (PAN) ... 

Stephens, E. R., Long-Path Infrared Spectroscopy for Air Pollution Research, Soc. Appl. Spectrosc., 12, 80-84 (1958). 

Tuazon EC, Winer AM, Graham RA, et al. 1981a. Atmospheric measurement of trace pollutants Long path fourier transform infrared spectroscopy. EPA- 600/S3-81-026. US EPA Research Triangle Park, NC. 

Coomber and Pitts (58) extended the abovementioned work by a study at wavelengths longer than 255 nm and 70-130°C. They found that (1) the major photodecomposition products were CO and propylene, and (2) small amounts of ethylene, allene, methyl-acetylene, cyclopropane, ethylketene, and enol-crotonaldehyde were also formed. Experiments with long-path infrared spectroscopy (LPIR) have shown that the quantum yields of ethylketene were 0.02 at X < 280 nm and -0.001 at X > 300 nm, whereas the quantum yields of enol-crotonaldehyde were very small at X <... 

Niki etal. (1977) have identified this product by long-path infrared spectroscopy in a study of the gas phase ozonolysis of ci s-2-butene. The occurrence of secondary ozonides in the gas-phase corresponds entirely to their production in the liquid phase at low temperatures (Criegee, 1957). These results led Dodge and Arnts (1979) to derive from a computer simulation of the experimental data of Niki et al. (1977) the following percentages... 

Using a similar technique, Nlkl and co-workers (151) have obtained rate constant data for the reaction of OH radicals with a series of aldehydes from their rates of disappearance, as measured by long path Fourier transform infrared spectroscopy. 

Various methods have been developed for remote gas sensing. These include differential optical-absorption spectroscopy (DOAS), differential absorption lidar (DIAL), and a number of methods that use spectroscopic methods with an atmospheric path in place of a laboratory long-path cell, for example tunable diode laser absorption spectroscopy (TDLAS) and Fourier transform infrared (FTIR) spectroscopy. 

The kinetics of reaction (Equation 4.45) for formaldehyde have been studied using long-path infrared (IR) and visible spectroscopy to follow the reactants and products in dilute mixtures of O3, NO and CH O (700 Torr) at room temperature [37]. It was accepted that only reactions (Equation 4.27), (Equation 4.28), (Equation 4.45) and (Equation 4.46) are important in the simplified reaction mechanism of the loss of CH O and N3O3/NO3. A more detailed consideration of the chemistry of the system... 

Liu K, Fellers RS, Viant MR, McLaughlin RP, Brown MG, Saykally RJ (1996) A long path length pulsed slit valve appropriate for high temperature operation infrared spectroscopy of jet-cooled large water clusters and nucleotide bases. Rev Sci Instnrm 67 410-416... 

U.S. Environmental Protection Agency, Compendium Method TO-16 Long-Path Open-Path Fourier Transform Infrared Spectroscopy of Atmospheric Gases, EPA 625R-96/010h, NTIS PB99-172355, Center for Environmental Research Information, Office of Research and Development, Cincinnati, OH, 1999. 

The Stable carbonyl and thiocarbonyl halide molecules have been studied by IR as well as Raman spectroscopy. Normal coordinate analyses based on force constants transferred from other molecules (Urey-Bradley type), or from ab initio calculations, have aided in the vibrational assignments. Some of the unstable molecules which have been observed in the microwave have been characterized by infrared spectroscopy. The somewhat lower sensitivity of this method means that long path lengths of the gas may be needed. The identification of the various stable and unstable species in the microwave spectrum is simplified by the fact that the absorption lines are usually well resolved from each other. The widths of the bands in the infrared may make the transient species difficult to detect against the stronger absorptions of the stable side products. IR and Raman spectroscopies do have the advantage that they can be used on solid and liquid samples. Since the bands in a low temperature rare gas matrix have a narrower profile, the infrared spectrum is usually simplified over the room temperature gas phase spectrum. Moreover, the vibrational frequencies are only mildly perturbed by solid state effects. For example, CF Se has not been observed in the vapor phase, yet its vibrational dynamics are known from its matrix isolation spectrum. Table 9 gives the vibrational data for the carbonyl, thiocarbonyl, seleno-carbonyl and formyl halides. 

The only study of the reaction of OH with iV-methylformamide is that conducted by Solignac et al. (2005). The measurements were performed using the relative rate technique in combination with long path Fourier transform infrared spectroscopy (ETIR). An unweighted mean of the values presented in table VUI-B-l obtained using three reference compounds gives k = 8.0 x 10 cm molecule s at 298 K with an estimated uncertainty of 35%. 

A major advantage of infrared absorption spectroscopy derives from the characteristic fingerprints associated with infrared-active molecules. On the other hand, interferences from common atmospheric components such as C02 and HzO are significant, so that the sensitivity and detection limits that can be obtained are useful primarily for polluted urban air situations. For atmospheric work, long optical path lengths are needed. 

If near-infrared diode lasers have low-noise characteristics similar to those of mid-infrared diode lasers, and thus minimum absorbances of 10 5 or less are possible, then an approximate detection limit can be calculated for an absorption experiment. For a 200-m optical path, the calculated detection limit is 5 x 1010 molecules/cm3, which is well above levels of H02 expected to be found in the atmosphere. An absorption experiment in this spectral region apparently would require extremely long optical path lengths, and, indeed, a calculation with a 5-km path yields a calculated detection limit of 2 x 109 molecules/cm3, still rather high for tropospheric measurements. Other issues associated with the use of diode lasers in absorption spectroscopy are discussed in the next section. 

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