Abstracts
Improvements in the Use of Attenuated Total Reflection - FT-IR Dichroism for Measuring Surface Orientation in Polymers
by *Neil J. Everall and Arran Bibby, ICI Research and Technology Centre, P.O. Box 90, Wilton, Middlesbrough, Cleveland, TS90 8JE, U.K.
Improvements in the use of attenuated total reflection (ATR) Fourier transform infrared (FT-IR) dichroism for measuring surface orientation in polymer films are described, with poly(ethylene terephthalate) (PET) as an example material. It is shown that normalizing band intensities relative to a nondichroic band, prior to calculating dichroic ratios, eliminates the need to maintain identical contact areas/pressures when removing, rotating, and reclamping samples to the ATR element, which has been a major historical drawback to this technique. The normalization is vital; it makes the calculated dichroic ratios largely insensitive to variations in sample/prism contact area, and less sensitive to uncertainties in the refractive indices and birefringence of the polymer. For PET, it is shown that the birefringence can be neglected in the analysis, and a single approximate refractive index used. This is a significant benefit since the birefringence will vary as a function of orientation and crystallinitv. Polymers that are much more birefringent than PET can also be analyzed by using the formalism described in this paper, provided that the three independent indices are known. This paper is presented in two parts; first, equations are derived which allow the calculation of all second-order orientation parameters (P 200, P 220, P 202 ,,and P 222), and the averaged squared direction cosines, from the normalized ATR dichroic ratios. Second, we show how a single-reflection diamond ATR unit is an ideal tool for this work, since it allows small, hard, or irregularly shaped samples to be examined without fear of damaging the ATR element. We illustrate the technique using data obtained from a series of uniaxially drawn films, and one biaxially drawn film, using a commercially available accessory. From these data, orientation parameters were calculated as a function of draw ratio and compared with those obtained from specular-reflectance FT-IR and birefringence analysis of the same samples. The method should be applicable to any polymer provided that (1) a suitable nondichroic band is available for normalization and (2) the largest polymer refractive index lies well below the ATR element (2.4 in the case of diamond). It must be realized that condition 1 is not trivial; careful investigation is required to identify truly nondichroic bands (if any exist for the polymer of interest.
Noise Sources in Step-Scan FT-IR Spectrometry
by *Christopher J. Manning and Peter R. Griffiths, Manning Applied Technology, 121 Sweet Avenue, Moscow, Idaho, 83843, USA
Step-scan Fourier transform infrared (FT-IR) spectrometry has been accepted as a useful tool for obtaining vibrational spectra of a variety of time-dependent systems. Unfortunately, a significant signal-to-noise ratio (SNR) disadvantage has been associated with the step-scan mode of data collection relative to the same data collection time with conventional rapid-scan FT-IR spectrometry. The key difference between the two methods is the average mirror velocity, which alters the dynamic range of the detector signal, as well as the frequencies of its components. The SNR disadvantage is shown to be related to low-frequency multiplicative fluctuations, caused in part by temperature variations, which convolve noise with measured spectra. Refractive index variations of air or purge gas in the paths of the infrared- and reference-laser radiation can be a particularly serious temperature-induced problem. The various noise sources are described, and experiments confirming that some are related to temperature variations are reported.
Trace Elements Analysis in Water by Laser-Induced Breakdown Spectroscopy Technique
by G. Arca, A. Ciucci, *V. Palleschi, S. Rastelli, and E. Tognoni, IFAM -- Istituto di Fisica Atomica e Molecolare del CNR, Via del Giardino, 7-56127 Pisa, Italy
In this paper, results are presented showing the feasibility of the laser-induced breakdown spectroscopy (LIBS) technique as a fast and sensitive analytic tool for quantitative measurement of trace elements in water. Many ionic elements were detected; the system linearity was tested by analyzing water samples containing known concentration of Mg and Ca, whereas Cr-polluted samples were exploited to test the system sensitivity limit to impurities.
Event-Locked Time-Resolved Fourier Spectroscopy
by H. Weidner and *R. E. Peale, Department of Physics, University of Central Florida, Orlando, Florida, 32816, USA
A low-cost method of adding time-resolving capability to commercial Fourier transform spectrometers with a continuously scanning Michelson interferometer has been developed. This method is specifically designed to eliminate noise and artifacts caused by mirror-speed variations in the interferometer. The method exists of two parts: (1) a novel timing scheme for synchronizing the transient events under study and the digitizing of the interferogram and (2) a mathematical algorithm for extracting the spectral information from the recorded data. The novel timing scheme is a modification of the well-known interleaved, or stroboscopic, method. It achieves the same timing accuracy, signal-to-noise ratio, and freedom from artifacts as step-scan time-resolving Fourier spectrometers by locking the sampling of the interferogram to a stable time base rather than to the occurrences of the HeNe fringes. The necessary pathlength-difference information at which samples are taken is obtained from a record of the mirror speed. The resulting interferograms with uneven pathlength-difference spacings are transformed into wavenumber space by least-squares fits of periodic functions. Spectra from the far-infrared to the upper visible at resolutions up to 0.2 cm -1are used to demonstrate the utility of this method.
Study of Diagnostic Criteria for Pathological Tissues by Laser-Induced Fluorescence
by *Lin Meirong, Lu Zhengrong, Fang Fang, Li Jia, and Zhang Baozheng, Institute of Modern Optics, Nankai University, Tianjin 300071, P. R. China
It has been confirmed that the differences in fluorescence spectra of normal and pathological biotissues can be used as a sensitive and nondestructive diagnostic probe. However, experiments show that not only are the fluorescence spectral features of different tissues very different but the features of the same tissue under different detection conditions are different too. Therefore, the diagnosis criteria of pathological tissues must be changed in accordance with different spectral features. In this paper, several diagnosis methods using native fluorescence characteristics of biotissues given in existing reports are analyzed. With the fourth harmonic at 266 nm of a Q-switched YAG laser as an excitation source, laser-induced fluorescence (LIF) spectra of native human normal and pathological breast and blood vessel tissues in vitro were measured and studied. According to their spectral characteristics, two diagnosis criteria are suggested: by the fluorescence intensity ratios at several specific wavelengths, cancerous (with p < 0.001) and benign tumor (p < 0.005) can be distinguished from the normal tissue; by the fluorescence intensity ratios of the two main peaks, atherosclerotic plague and thrombus (both with p < 0.005) can be distinguished from normal blood vessel. In order to make comparisons with the results from human cancerous breast tissues, spectra of a model mouse were also observed
Classification of Vegetable Oils by FT-IR
by *Donald B. Dahlberg, Shawn M. Lee, Seth J. Wenger, and Julie A. Vargo, Applied Chemometrics, Department of Chemistry, Lebanon Valley College, Annville, Pennsylvania, 17003, USA
The Fourier transform infrared (FT-IR) spectra of 27 brands of 10 types of cooking oils and margarines were measured without temperature control. Attempts to predict the vegetable source and physical properties of these oils failed until wavelength selection and multiplicative signal correction (MSC) were applied to the FT-IR spectra. After pretreatment of the data, principal component analysis (PCA) was totally successful at oil identification, and partial least-squares (PLS) models were able to predict both the refractive indices [standard error of estimation (SEE) 0.0002] and the viscosities (SEE 0.52 cP) of the oils. These models were based predominately on the FT-IR detection of the cis and trans double-bond content of the oils, as well as small amounts of defining impurities in sesame oils. Efforts to use selected wavelengths to discriminate oil sources were only partially successful. These results show the potential utility of FT-IR in the fast detection of substitution or adulteration of products like cooking oils.
On-Line Monitoring of Laser Cleaning of Limestone by Laser-Induced Breakdown Spectroscopy and Laser-Induced Fluorescence
by *I. Gobernado-Mitre, A. C. Prieto, V. Zafiropulos, Y. Spetsidou, and C. Fotakis, Department of Condensed Matter Physics, Crystallography and Mineralogy, University of Valladolid, 47011 Valladolid, Spain
The application of laser-induced breakdown spectroscopy (LIBS) to monitor the laser cleaning process of polluted limestone from a historic building is examined. The combination of a Q-switched Nd: YAG pulsed laser with on-line diagnostics by the LIBS technique is shown to be very useful for controlling and characterizing the cleaning process in order to avoid overcleaning. In addition, the coupling of this spectroscopic technique to the cleaning process provides important information about the optimal experimental conditions to be selected for achieving an adequate cleaning procedure. Furthermore, the spectroscopic study of the plasma emission can be used to determine the elemental composition of both the black crust and the underlying stone. The application of LIBS as a diagnostic technique to monitor and control the laser cleaning process of limestone is based on the different elemental composition of the black encrustations covering the stone surface and the underlying stone. On the other hand, a different experimental setup for probing the ablation products by laser-induced fluorescence (LIF), in order to achieve a signal amplification of some atomic emission lines with weak intensity in the LIBS spectrum, is described.
Photodegradation in Ballistic Laminates: Spectroscopy and Lifetime Extension
by *Clifford L. Renschler, Brian R. Stallard, Christine A. White, Manuel J. Garcia, and Harvey E. Morse, Sandia National Laboratories, Albuquerque, New Mexico, 87185-0367, USA
Polycarbonate (PC), a critical component in ballistic laminates (BLs), is known to degrade upon exposure to ultraviolet (UV) light. For the purpose of reducing the photodegradation, a UV blocking chemical has been added to the adhesives used to join the layers of the BL. This report describes the development of a spectroscopic method for monitoring surface photodegradation of PC and the method's use in demonstrating the effectiveness of the UV blocker. Reports in the literature demonstrate that photodegradation in thin PC films may be detected by transmission infrared (IR) spectroscopy. The present work extends this approach to thick films, where small surface changes are detected by reflectance IR spectroscopy. We show that UV photodegradation of the PC surface produces a characteristic shift in the carbonyl absorption band at about 1775 cm -1. This shift is consistently observed in PC samples that have been subjected to direct artificial exposure and in PC samples that have been subjected through the outboard layers of the BL to both natural and artificial exposure. When a UV blocker is incorporated into the adhesive layers of the laminate, no peak shift is observed in the carbonyl band after the equivalent of 10 years of exposure.
Investigation of the Degradation Products of Archaeological Linens by Raman Spectroscopy
by *H. G. M. Edwards and M. F. Falk, Chemistry and Chemical Technology, University of Bradford, Bradford BD7 IDP, U.K.
The yellow-brown coloration formed in the degradation process of linen fabrics has been studied by Raman spectroscopy. Aqueous extracts from documented linens from the Egyptian XIIth Dynasty (ca. 4000 y BP) and Kasr-el-Yahud (ca. 1350 y BP) have been used to investigate the chemical basis of the degradation process; the pale-yellow crystalline material isolated from these extracts shows evidence of OH, C=C, C -- C, and hydrocarbon groups. Several possibilities for the ring scission of cellulose under archaeological conditions are addressed.
Imaging Neurotransmitter Uptake and Depletion in Living Astrocytes
by *Weihong Tan, Philip G. Haydon, and Edward S. Yeung, Ames Laboratory -- USDOE and Department of Chemistry, Iowa State University, Ames, Iowa, 50011, USA
An ultraviolet (UV) laser-based optical microscope and charge-coupled device (CCD) detection system was used to obtain chemical images of biological cells. Subcellular structures can be easily seen in both optical and fluorescence images. Laser-induced native fluorescence detection provides high sensitivity and low limits of detection, and it does not require coupling to fluorescent dyes. We were able to quantitatively monitor serotonin that has been taken up into and released from individual astrocytes on the basis of its native fluorescence. Different regions of the cells took up different amounts of serotonin with a variety of uptake kinetics. Similarly, we observed different serotonin depletion dynamics in different astrocyte regions. There were also some astrocyte areas where no serotonin uptake or depletion was observed. Potential applications include the mapping of other biogenic species in cells as well as the ability to image their release from specific regions of cells in response to external stimuli.
Use of Pyrolysis Mass Spectrometry with Supervised Learning for the Assessment of the Adulteration of Milk of Different Species
by Royston Goodacre, Institute of Biological Sciences, University of Wales, Aberystwyth, Dyfed, SY23 3DA, U.K.
Binary mixtures of 0-20% cows' milk with ewes' milk, 0-20% cows' milk with goats' milk, and 0-5% cows' milk with goats' milk were subjected to pyrolysis mass spectrometry (PyMS). For analysis of the pyrolysis mass spectra so as to determine the percentage adulteration of either caprine or ovine milk with bovine milk, partial least-squares regression (PLS), principal components regression (PCR) and fully interconnected feed-forward artificial neural networks (ANNs) were studied. In the latter case, the weights were modified by using the standard back-propagation algorithm, and the nodes used a sigmoidal squashing function. It was found that each of the methods could be used to provide calibration models which gave excellent predictions for the percentage adulteration with cows' milk to <1% for samples, with an accuracy of F0.5%, on which they had not been trained. Scaling the individual nodes on the input layer of ANNs significantly decreased the time taken for the ANNs to learn, compared with scaling across the whole mass range; however in one case this approach resulted in poor generalization for the estimates of percentage cows' milk in ewes' milk. To assess whether the calibration models had learned the differences between the milk species or the differences due to the different fat content of in each of the milk types, we also analyzed pure milk samples varying in fat content by PyMS. Cluster analysis showed unequivocally that the major variation between the different milk species was not due to variable fat content. Since any biological material can be pyrolyzed in this way, the combination of PyMS with supervised learning constitutes a rapid, powerful, and novel approach to the quantitative assessment of food adulteration generally.
Nondestructive Discrimination of Biological Materials by Near-Infrared Fourier Transform Raman Spectroscopy and Chemometrics: Discrimination among Hard and Soft Ivories of African Elephants and Mammoth Tusks and Prediction of Specific Gravity of the Ivories
by Masahiko Shimoyama, Hisashi Maeda, Hidetoshi Sato, *Toshio Ninomiya, and *Yukihiro Ozaki, Forensic Science Laboratory, Hyogo Prefectural Police Headquarters, Shimoyamate-dori, Chuo-ku, Kobe 650, Japan (T.N.), Department of Chemistry, School of Science, Kwansei-Gakuin University, Uegahara, Nishinomiya 662, Japan
This paper demonstrates the usefulness of near-infrared (NIR) Fourier transform (FT) Raman spectroscopy and chemometrics in nondestructive discrimination of biological materials. The discrimination among three kinds of materials -- hard ivories, soft ivories, and mammoth tusks -- has been investigated as an example. NIR (1064-nm) excited FT-Raman spectra were measured in situ for these materials, and principal component analysis (PCA) of the obtained spectra was carried out over the 1800-400-cm-1 region. The two kinds of ivories are clearly discriminated from one another on the basis of a one-factor plot. It was found that treatment of the Raman data by multiplicative scatter correction (MSC) greatly improves the ability to discriminate. Principal component weight loadings show that the discrimination relies upon the ratio of collagen and hydroxyapatite included in two kinds of ivories. The discrimination among the hard and soft ivories and mammoth tusks was made by a three-factor plot for FT-Raman spectra after the MSC treatments. Partial least-squares regression (PLSR) enabled us to make a calibration model which predicts the specific gravity of the hard and soft ivories.
Instrumental Resolution Considerations for FT-IR Gas Phase Spectroscopy
by P. Jaakkola, *J. D. Tate, M. Paakkunainen, J. Kauppinen, and P. Saarinen, Dow Chemical USA, 2301 Freeport, Texas, 77541, U.S.A.
Instrumental resolution has a significant effect on the performance of Fourier transform infrared (FT-IR) spectrometers used for gas-phase analysis. Low-resolution FT-IR spectroscopy offers some valuable advantages compared with the traditional high-resolution FT-IR gas-phase spectroscopy, especially in nonlaboratory environments. First, high signal-to-noise ratio (SNR) spectra can be acquired in field conditions without the use of traditional liquid nitrogen-cooled detectors. Second, the dynamic range for quantitative analysis is larger for low-resolution spectroscopy than for high-resolution due to the lower absorbance values and lower noise levels. Third, spectral analysis speed is increased and data storage requirements are substantially reduced. The purpose of this study was to investigate the effect of instrumental resolution on FT-IR gas-phase analysis. The effects of spectral resolution on sensitivity, selectivity, accuracy, precision, spectral overlap, dynamic range, and nonlinearity are separately discussed.
Study on Surface-Enhanced IR-Adsorption Spectroscopy (SEIRAS) Over Evaporated Au Films in an Ultra-High Vacuum System
by *Shinri Sato and Toshihiro Suzuki, Catalysis Research Center, Hokkaido University, Sapporo 060, Japan
IR transmission spectra were measured in an ultrahigh vacuum system for Fe(CO)5, n-decane, and NH3 adsorbed at <150 K on transparent Au films evaporated on a sapphire plate. The spectra of Fe(CO)5 show 10-fold enhancement as compared to those observed on an SiO2 film coated on a sapphire plate, which has been reported as surface-enhanced IR-absorption (SEIRA). The enhancement is reduced when the coverage of adsorbate exceeds a mono-layer or other molecules present on the surface prior to adsorption, indicating that SEIRA is effective only in the close vicinity of the surface. The SEIRA effect is also reduced when film is heated in a vacuum, probably because of sintering of the Au particles forming the film. In addition, the heat treatment of the film results in blue shifts of bands, accompanied by some band distortion. With the use of SEIRAS, the surface photochemistry of Fe(CO)5 has been investigated.
Quantitation of Poly(ethylene glycol) Concentration Using Raman Spectroscopy
by Yanira MelJndez, Kimberley F. Schrum, and *Dor Ben-Amotz, Department of Chemistry, Purdue University, West Lafayette, Indiana, 47907-1393, USA
This study uses Raman spectroscopy to quantitate the amount of polymer in solution, in particular poly (ethylene glycol) dissolved in chloroform. For various chain lengths and polymer weight fraction ranges, it is shown that the ratios of peak intensities in the C -- H stretching region may be used to quantitate polymer weight fraction with about 1% uncertainty. For low polymer weight fraction ranges (0-10%), the relationship between Raman intensity and polymer weight fraction is essentially linear, while at higher ranges (0-50%) the intensity follows a nonlinear function derived from basic concentration relationships and indicates a universal scaling with polymer chain length.
Interpolation of Spectral Data Using the Shift Theorem of the Discrete Fourier Transform
by Sisko Maria Eskola and *Folke Stenman, Department of Physics, Accelerator Laboratory, University of Helsinki, P.O.B. 9, 00014 Helsinki, Finland
We present a method for interpolating discrete spectral data using the shift theorem of the discrete Fourier transform. The advantages of the method as compared to ordinary curve fitting and similar direct interpolation methods are that, being based on the discrete courier transform, our method is also very fast for large sample volumes if used with the fast Fourier transform (FFT) algorithm. In contrast to direct interpolation methods in spectral space, our method does not modify the modulus of the inverse Fourier transform of the shifted profile, so that the spectral content of the signal is preserved. The basis of the method also makes it suitable for analyzing hot-band structures in vibrational spectra. The method is illustrated with two examples.
Elemental Fractionation in Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS)
by *Deborah Figg and Michael S. Kahr, CST-9, Chemical Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA
Three laser wavelengths (1064, 532, and 266 nm) were employed for laser ablation at varied laser pulse energies to study the effect of irradiance and wavelength upon analytical results for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Two important results were observed and are reported here: (1) the intensity of the MS signal came to a local minimum when the laser focal point was on the sample surface, and (2) elemental fractionation based upon laser wavelength and laser pulse energy was observed. For the waste glass simulant studied, ablation with 1064-nm (IR) and 532-nm (green) radiation produced elemental fractionation that relates to the melting point of the elemental oxide, whereas with 266-nm (UV) ablation the response was independent of the elemental oxide melting point. At high laser powers, ablation at 266 nm produced an elemental bias based upon the mass of the elements. These observations suggest the use of ultraviolet radiation at low pulse energies to obtain improved analytical results.
Three New Organic Scintillators with Large Stokes Shifts
by E. Barni, G. Viscardi, *C. D'Ambrosio, H. Leutz, D. Puertolas, S. Tailhardat, P. Destruel, P. Jolinat , and H. Ghsten, CERN, Geneva, Switzerland
Three new organic scintillators (PMP-410, PMP470, and PMP480) were synthesized on the basis of 1-phenyl-3-mesityl-2-pyrazoline (PMP). Their synthesis and their polymerization in polystyrene are described. We measured their Stokes shifts in polystyrene (-1.3 eV) between their absorption maxima (PMP-410: 287 nm; PMP-470: 315 nm; PMP-480: 314 nm) and their emission maxima (PMP-410: 408 nm; PMP-470: 480 nm; PMP-480: 479 nm). Absorption and emission maxima, Stokes shifts, and light yields of all eight pyrazoline scintillators so far synthesized are listed and are compared with results for 3-hydroxyflavone (3-HF). The advantages of these one-component dopants are discussed with respect to the usually applied two-component (scintillator plus wavelength shifter) dopants.
Determination of Protein in Ground Wheat Samples by Mid-Infrared Diffuse Reflectance Spectroscopy
by *James B. Reeves III and Stephen R. Delwiche, USDA, Agricultural Research Service, NCML, LPSI, Bldg. 200, Rm 124, Beltsville, Maryland 20705, USA
The objective of this study was to determine whether mid-infrared diffuse reflectance spectroscopy could be used in the same manner as near-infrared diffuse reflectance spectroscopy to quantitatively determine the protein content of ground wheat samples. One hundred and thirty hard red winter wheat samples were assayed for protein by combustion and scanned in the near- and mid-infrared. Samples (UDY ground) were scanned neat in the near-infrared from 1100 nm (9091 cm-1) to 2498 nm (4003 cm-1) on a scanning monochromator and in the mid-infrared from 4000 cm-1 (2500 nm) to 400 cm-1 (25,000 nm) on a Fourier transform spectrometer at 4and 16-cm ' resolutions. Protein content varied from a low of 8.98% to a high of 18.70% (average of 12.86% with a standard deviation of 1.66%). Calibrations developed with the use of partial least-squares gave an R2 and bias-corrected standard error of performance of 0.999 and 0.054 for the near-infrared and 0.997 and 0.085 for the mid-infrared (4 cm-1 resolution). Calibration results based on mid-infrared spectra, while not as good as those for near-infrared spectra, were nevertheless quite good. These results demonstrate that it is possible to develop satisfactory calibrations for protein in ground wheat with the use of mid-infrared spectra without the need for sample dilution with KBr.
Urinary Stone Layer Analysis of Mineral Components by Raman Spectroscopy, IR Spectroscopy and X-Ray Powder Diffraction: A Comparative Study
by *C. G. Kontoyannis, N. C. Bouropoulos, and P. G. Koutsoukos, Institute of Chemical Engineering and High Temperature Chemical Processes, University of Patras, GR 26500 Patras, Greece
Mineral components of a urinary stone forming layers have been analyzed with the use of Raman spectroscopy (RS), Fourier transform infrared spectroscopy (FT-IR), and X-ray powder diffraction (XRD). The three spectroscopic methods were compared with respect to their capability of yielding reliable analytical qualitative results. The application of RS yielded less crowded spectra with sharper bands in comparison with those obtained by FT-IR. The analysis of the various mineral layers found in a human stone was possible with RS by focusing the laser beam at the desired layer. Overlapping broad bands were produced from the application of FT-IR, which made it difficult to identify components whose bands showed overlapping. Powder XRD could not be used for accurate analysis of the mineral components of the various stone layers since the material contained in the layers of small stones is not sufficient for analytical purposes. Moreover, the necessary stone grinding precludes the possibility of mineral topological analysis.
Optimal Wavelength Range Selection by a Genetic Algorithm for Discrimination Purposes in Spectroscopic Infrared Imaging
by W. H. A. M. van den Broek, D. Wienke, W. J. Melssen, and *L. M. C. Buydens, Catholic University of Nijmegen, Laboratory for Analytical Chemistry, Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
When spectroscopic infrared imaging is applied to discriminate between different materials, multiple images have to be measured at different wavelengths or wavelength ranges. The time-consuming step in present on-line spectroscopic imaging is the measurement and processing time per identification of a number of spectroscopic images. If this number of images can be kept small, whereby an optimal discrimination is still guaranteed, the acquisition and processing time will be faster and, therefore, this approach becomes attractive in real-world applications. This paper describes the search for a limited number of spectroscopic wavelengths or wavelength ranges for images where optimal discrimination between the materials is guaranteed. This optimization is applied in particular to the discrimination between plastics and nonplastics. Because the number of potential wavelength combinations is huge, a genetic algorithm (GA) is used as a subset selection technique to solve this large-scale optimization problem. Since the problem concerns classification, a specific optimization criterion is developed. Finally, infrared images are measured at the calculated optimal wavelength ranges, and the resulting discrimination performance is compared with that of images measured at wavelengths chosen on the basis of a priori spectroscopic knowledge.
Examination of the Photochemical Curing and Degradation of Oil Paints by Laser Raman Spectroscopy
by Seiichiro Higuchi, Tosimitsu Hamada, and *Yohichi Gohshi, Department of Applied Chemistry, Faculty of Engineering, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan
In the present study, the curing and the degradation of oil paints by irradiation with ultraviolet light was investigated by laser Raman spectroscopy. At present, the curing reaction of oil paints is interpreted by several reaction schemes, although none of them is considered to be based on definite experimental evidence. The most typical examples are as follows: one is the radical termination reaction of the crosslinking type; the other, the polymerization reaction of the Diels -- Alder reaction (diene reaction) type. In the present investigation, oil paint film (ZnO White and TiO2 White) was irradiated with a Xe lamp, and the time dependence of the Raman spectra of the films was examined. It is shown that the curing reaction cannot be explained by either of the above-mentioned reaction schemes. A new reaction mechanism for the curing and the degradation of paint films is proposed. It is concluded that the microscopic approach to the elucidation of the degradation mechanism of oil paint films based on Raman spectroscopy is very useful for the improvement of oil painting techniques.
Ultraviolet-363.8 nm Raman Spectroscopic System for in situ Measurements at High Temperatures
by *Masatomo Yashima, Masato Kakihana, Ryosuke Shimidzu, Hirotaka Fujimori, and Masahiro Yoshimura, Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Nagatsuta 4259. Midori-ku, Yokohama, 226, Japan
A new ultraviolet (UV) Raman spectroscopic system to measure the Raman scattering from materials at high temperatures up to 1500 ºC has been designed. This system is based on a CW (continuous-wave) ultraviolet argon-ion laser (363.8 nm), a spatial filter, a single monochromator coupled to a double-grating rejection filter, and a two-dimensional charge-coupled device (CCD) detector. The plasma lines from the laser are almost completely rejected by a Pellin -- Broca prism combined with apertures. In situ Raman measurements for a zirconia (ZrO2) specimen at various high temperatures have been performed by using the UV excitation as well as the conventional visible 488.0-nm excitation for comparison. In the case of visible excitation, thermal emission obstructs the observation of the Raman scattering from zirconia even at 900 ºC; it becomes rapidly pronounced between 900 and 1100 ºC, and finally it is impossible to observe Raman spectra at temperatures higher than 1200 ºC. In sharp contrast to the visible excitation, the UV excitation provides good-quality Raman spectra with practically flat backgrounds for the Raman signal of tetragonal zirconia in the spectral region of 20 -- 1100 cm-1 even at 1500 ºC, and it enables clear observation of the monoclinic-tetragonal phase transformation of zirconia occurring between 1100 and 1200 ºC.
Two-Dimensional Imaging of Flame-Species Using Two-Photon LIF
by Nikola Georgiev and *Marcus Alden, Department of Combustion Physics, Lund Institute of Technology, P. O. Box 118, S-221 00 Lund, Sweden
The potential for two-dimensional visualization of combustion species by using two-photon laser-induced fluorescence (LIF) has been investigated. The technique was applied for two-dimensional (2D) imaging of carbon monoxide, ammonia, oxygen, and hydrogen atoms in flames. Approaches for compensating the signal intensity for the quadratic laser intensity dependence in two-photon imaging are discussed. For the case of CO and H atom visualization, a potential problem is the interference from nonresonantly excited C2, whose emission spectrally and spatially coincides with the fluorescence from CO. Different strategies for elimination of the C2 emission were investigated. It was found out that the emissions from CO and C2 can be separated in time. For the case of the oxygen atoms, it was observed that the relation between the intensities of the fluorescence signals at 845 and 777 nm changes with the equivalence ratio of the investigated flame. An attempt to estimate the 2D detection limit for these species in flames is also made.
Phase-Resolved Depth Profiling of Thin-Layered Plasma Polymer Films by Step-Scan Fourier Transform Infrared Photoacoustic Spectroscopy (S2FTIR PAS)
by Eric Y. Jiang, *Richard A. Palmer, Nancy E. Barr and Nicholas Morosoff, Department of Chemistry, Duke University, Durham, North Carolina 27708
After reviewing the background of step-scan interferometric photo-acoustic spectroscopy, this paper describes a step-scan Fourier transform photoacoustic phase-resolved technique and its applications in depth profiling of micrometer-thick layered plasma polymers. In particular, the power of direct use of the photoacoustic phase spectrum in both qualitative and quantitative depth profiling of the layered samples is extensively discussed. The effects of both spatial origin and intensity of a photoacoustic signal on its phase have been explicitly analyzed for both overlapping and distinctive, nonoverlapping, bands of the thin-layered plasma polymer samples. The phase spectrum technique is shown to be a very effective and efficient method of spectral depth profiling analysis.
Rapid Communication Study of Impulse Polymer Rheo-Optics by Step-Scan FT-IR Time-Resolved Spectroscopy (S2FT-IR TRS)
by Haochuan Wang, *Richard A. Palmer, and Christopher J. Manning, Department of Chemistry, Duke University, Durham, North Carolina 27708-0346
The applicability of step-scan impulse/response FT-IR spectroscopy to the rheo-optical study of polymer films is demonstrated by spectral measurements with isotactic polypropylene. A novel piezoelectrically driven microrheometer is employed to apply repetitive impulses to a polymer sample while time-domain spectra are recorded by step-scan FT-IR spectroscopy. The traditional advantages of Fourier transform spectroscopy are retained while providing a second multiplex advantage for the characterization of the time-dependence of the sample response. Reproducible results, consistent-with the frequency-domain literature data and having good signal-to-noise ratio, are obtained. The spectral changes due to molecular reorientation are found to be essentially as fast as the mechanical stretching, also consistent with frequency-domain results. To our knowledge, this is the first reported step-scan FT-IR time-domain rheo-optical measurement. This technique appears to be applicable to a variety of polymer samples. The advantages of time-domain measurements over frequency-domain measurements are briefly discussed.
Calculating Inaccessible Raman Reference Spectra for Use in Monitoring a Suspension Polymerization
by Thomas J. Vickers, Daniel R. Lombardi, Bin Sun, Hsiaoling Wang, and *Charles K. Mann, Department of Chemistry, Florida State University, Tallahassee, Florida 32306-3006, USA
Reduction of Stray Light in Monostatic Open Path FT-IR Spectrometers with a Plane Correction Mirror
by R. L. Richardson and *P. R. Griffiths, Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, USA