| 1. |
- Axelsson, H, et al.
(författare)
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Measurement of Aromatic-hydrocarbons With the DOAS Technique
- 1995
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 49:9, s. 1254-1260
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Tidskriftsartikel (refereegranskat)abstract
- Long-path DOAS (differential optical absorption spectroscopy) in the ultraviolet spectral region has been shown to be applicable for low-concentration measurements of light aromatic hydrocarbons. However, because of spectral interferences among different aromatics as well as with oxygen, ozone, and sulfur dioxide, the application of the DOAS technique for this group of components is not without problems. This project includes a study of the differential absorption characteristics, between 250 and 280 nm, of twelve light aromatic hydrocarbons representing major constituents in technical solvents used in the automobile industry. Spectral overlapping between the different species, including oxygen, ozone, and sulfur dioxide, has been investigated and related to the chemical structure of the different aromatics. Interference effects in the DOAS application due to spectral overlapping have been investigated both in quantitative and in qualitative terms, with data from a field campaign at a major automobile manufacturing plant.
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| 2. |
- Ferry, Anders, et al.
(författare)
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Curve fitting and deconvolution of instrumental broadening : a simulated annealing approach
- 1995
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Ingår i: Applied Spectroscopy. - : Sage Publications. - 0003-7028 .- 1943-3530. ; 49:3, s. 273-278
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Tidskriftsartikel (refereegranskat)abstract
- A curve-fitting procedure based on the simulated annealing algorithm has been developed for the analysis of spectral Raman data. By the inclusion of a priori information about the instrumental broadening in the definition of the cost function that is minimized, effects of the finite instrumental resolution are eliminated from the resulting fit. The ability of the method to reproduce original band shapes is tested on synthesized spectra and FT-Raman spectra of diamond recorded at different resolutions with different apodization functions. The procedure yields the global optimum of the fitted parameters and is easily implemented on a personal computer.
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| 3. |
- Johansson, Ursula, et al.
(författare)
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Raman spectroscopy of the kaolinite hydroxyls at 77 K
- 1998
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 52:10, s. 1277-1282
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Tidskriftsartikel (refereegranskat)abstract
- Raman spectroscopy of two types of kaolinites has been obtained at liquid nitrogen temperature (77 K) with the use of a Raman microprobe and a thermal stage. The Raman spectrum is characterized by the combination of the frequencies of the inner hydroxyl and the inner surface hydroxyl groups. The inner hydroxyl frequency is reduced, and the outer hydroxyl frequencies move to higher frequencies upon cooling to 77 K. The inner hydroxyl frequency shifts from 3620 cm-1 at 298 K to 3615 cm-1 at 77 K. The two in-phase inner surface hydroxyl frequencies move from 3684 and 3689 cm-1 at 298 K to 3690 and 3699 cm-1 at 77 K. The two out-of-phase vibrations shift from 3650 and 3668 cm-1 to 3656 and 3675 cm-1. The bandwidth of the inner hydroxyl frequency decreases from 3.7 to 2.1 cm-1 at 77 K. The bandwidth of the inner surface hydroxyl frequency (upsilon 1) increases upon cooling from 17.4 to 19.2 cm-1. It is proposed that the increased resolution at low temperature enabled an additional inner surface hydroxyl frequency to be observed.
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| 4. |
- Li, TQ
(författare)
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H-2 NMR spectra for D2O adsorbed on oriented cellulose fibers
- 1996
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Ingår i: APPLIED SPECTROSCOPY. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 50:12, s. 1512-1518
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 2H NMR spectra for D2O adsorbed on cellulose fibers which are macroscopically oriented demonstrate that the axis of cellulose fibers can be regarded as the director of the average molecular motion of the adsorbed D2O. The spectra for samples prepared from fiber sheets depend on the orientation of the sheets with respect to the magnetic field as well as the fiber orientation in the sheets. When the sheets are oriented perpendicular to the magnetic field, all the fibers in the sheets are perpendicular to the field irrespective of the fiber orientations in the sheets, and a partially overlapped quadrupole splitting is observed. When the sheets are oriented parallel to the magnetic field, the observed spectra deviate significantly from the expected 2D powder patterns, and the distribution of fiber orientations in the sheets has a significant influence on the observed band shape. An N-site mutual exchange model was used to account for the lateral diffusion of water molecules from one fiber to another. In a comparison of the simulated spectra based on the N-site mutual exchange model with the experimentally recorded spectra, the average lifetime for the adsorbed D2O molecules to reside on cellulose fibrils was estimated to be about 1.5 ms.
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| 5. |
- Yedur, Sanjay K, et al.
(författare)
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Use of fluorescence spectroscopy in concentration and supersaturation measurements in citric acid solutions
- 1996
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 50:7, s. 866-870
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Tidskriftsartikel (refereegranskat)abstract
- Measurement of supersaturation is of critical importance in the operation and control of crystallizers. In this work, we report a novel spectroscopic technique to achieve the measurement of concentration and supersaturation in crystallizing solutions. In order to develop a sensor for this measurement, citric acid is chosen as the model solute, and the analytical technique involves fluorescence spectroscopy. Citric acid is a common food-grade compound with a wide range of applications that is exclusively produced by crystallization. The fluorescent properties of a probe, 8-hydroxy-1,3,6-pyrenetrisulfonate (pyranine), are used to provide concentration measurements in aqueous citric acid solutions, thereby providing for supersaturation estimation. The change in the relative emission peak intensities of the probe in different solute concentrations gives an excellent calibration curve for concentration measurements. It is also shown that, although pyranine responds to both its solvent microenvironment and the pH of the solution, it is still possible to measure concentration and supersaturation by using this fluorescence technique.
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| 6. |
- Bengtsson, Per Erik
(författare)
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Simultaneous two-dimensional visualization of soot and OH in flames using laser-induced fluorescence
- 1996
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Ingår i: Applied Spectroscopy. - 0003-7028. ; 50:9, s. 1182-1186
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional visualization of soot has been realized in flames with the use of laser-induced fluorescence in C2 from laser-vaporized soot [LIF(C2)LVS]. Soot particles are heated to vaporization temperatures by the absorption of laser radiation. C2 radicals produced by this process are excited at wavelengths around 563 nm through the transition ν′ = 0 d3∏g←ν″ = 1 a3∏u, and the subsequent fluorescence at approximately 516 nm is detected. By frequency-doubling of the laser radiation, wavelengths around 281.5 nm are achieved, which can excite OH radicals to the ν′ = 1 A2Σ+ state from ν″ = 0 X2∏, with subsequent fluorescence at approximately 310 nm. With the use of both these excitation wavelengths, and a Cassegrainian split-mirror telescope as the imaging detection system in front of the charge-coupled device (CCD) camera, simultaneous two-dimensional single-shot images of soot and OH were obtained on a single CCD chip, thus enabling both sooting regions and reaction zones in flames to be monitored.
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