Absorption infrared spectroscopy

Of all the physical techniques, infrared spectroscopy gives perhaps the most valuable information about the constitution of organic materials. Indeed, qualitative information about specific structural elements can often be surmised even though the spectra are too complex for individual compound analysis. 

FIGURE 10.4 Relative abundances of aromatic and heteroaromatic units from oxidation of lignite, bituminous coal, and anthracite. (From Hayatsu, R. et al.. Fuel, 57, 541, 1978.) 

Source Speight, J.G., Analytical Methods for Coal and Coal Products, C. Karr, Jr., Ed., Academic Press, Inc., New York, 1978, Vol. II, Chapter 22. 

The absorption band at 3030 cm (aromatic CH), which appears in a coal with 81% carbon, becomes more pronounced as coal rank increases while the band at 2920 cm generally increases with rank to 86% carbon but decreases sharply thereafter. The assignment of absorptions in the infrared spectra to various oxygen functions has also received some attention (Table 10.6) (Speight, 1978). 

Pyridine extraction of coal appears to afford, as indicated by infrared absorption studies, a two-component system, one rich in carbonyl and hydroxyl functions and the other in nonaromatic 

The two key performance metrics for a sensing technique are specificity and sensitivity. Specificity of IR absorption spectroscopy relies on identification of characteristic absorption lines of target molecules at particular wavelengths. In a dilute gaseous medium at room temperature, spectral widths of small-molecule absorption 

Sensitivity of waveguide evanescent wave sensors can be conveniently analyzed using the Lambert-Beer law. The intensity reduction AI due to target molecule absorption through a waveguide section of length L is given by 

On-chip analyte transport can be realized by integrating microfluidic flow systems or miniaturized gas chambers with the sensor device [69]. Hu et al. demonstrated a microfluidic sensor device monolithically integrated with planar Ge-Sb-S ChG waveguides [70]. Quantitative chemical sensing via evanescent wave absorption spectroscopy was demonstrated using the microfluidic device. 

Sensitivity of resonant cavity sensors operating in the absorption spectroscopy mode was both theoretically and experimentally investigated by several groups [78-80]. The effective optical path length Lgg in a resonant cavity at resonance X can be estimated by the following formula  

Here F is the cavity finesse and the factor F/2n manifests the optical path length enhancement effect with respect to the cavity physical length at the resonance wavelength. Similar to waveguide evanescent sensors, the sensitivity of resonator sensors is also ultimately bounded by intrinsic propagation loss in the device. 

The most analytically useful region of the IR spectrum is 2.5 15 pm (wave numbers 4000 650 cm ). In this region, most organic compounds produce a 

IR spectrometers have the same components as UY/visible, except the materials need to be specially selected for their transmission properties in the IR (e.g., NaCl prisms for the monochromators). The radiation source is simply an inert substance heated to about 1500 °C (e.g., the Nernst glower, which uses a cylinder composed of rare earth oxides). Detection is usually by a thermal detector, such as a simple thermocouple, or some similar device. Two-beam system instruments often work on the null principle, in which the power of the reference beam is mechanically attenuated by the gradual insertion of a wedge-shaped absorber inserted into the beam, until it matches the power in the sample beam. In a simple ( flatbed ) system with a chart recorder, the movement of the mechanical attenuator is directly linked to the chart recorder. The output spectrum is essentially a record of the degree of 

In mathematical terms, the relationship between the interferogram in FTIR and the absorbance spectrum obtained by conventional IR is that the interferogram is the Fourier transform of the absorbance spectrum - hence the term FTIR. Application of an inverse Fourier transform to the interferogram, therefore, converts the output of the FTIR into a conventional display. 

It can be shown that the mathematical form of a pure cosine interferogram (P( 5), where 5 is the phase difference between the two beams) can be expressed as  

We can consider a real interferogram to be the summation of an infinite number of cosine terms, or  

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Wang C, Mohney B K, Williams R, Hupp J T and Walker G C 1998 Solvent control of vibronic coupling upon intervalence charge transfer excitation of (NC)gFeCNRu(NH3)g- as revealed by resonance Raman and near-infrared absorption spectroscopies J. Am. Chem. Soc. 120 5848-9... 

K. Nakanishi, Infrared Absorption Spectroscopy, Holden-Day, Inc., San Francisco, 1962. 

The Raman spectrum of an oxide sample after adsorption may be considered to consist of the spectrum of the adsorbed species superimposed on the spectrum due to the oxide adsorbent. In general, the Raman spectra of oxide adsorbents are sufficiently weak or sufficiently simple that they allow the detection of Raman lines due to the adsorbed species. This is one major advantage of Raman scattering over infrared absorption spectroscopy. The infrared spectra of most oxide adsorbents show strong absorptions which may obscure those arising from the adsorbates (Figs. 13,14). 

A nano-light-source generated on the metallic nano-tip induces a variety of optical phenomena in a nano-volume. Hence, nano-analysis, nano-identification and nanoimaging are achieved by combining the near-field technique with many kinds of spectroscopy. The use of a metallic nano-tip applied to nanoscale spectroscopy, for example, Raman spectroscopy [9], two-photon fluorescence spectroscopy [13] and infrared absorption spectroscopy [14], was reported in 1999. We have incorporated Raman spectroscopy with tip-enhanced near-field microscopy for the direct observation of molecules. In this section, we will give a brief introduction to Raman spectroscopy and demonstrate our experimental nano-Raman spectroscopy and imaging results. Furthermore, we will describe the improvement of spatial resolution... 

Osawa, M Tsushima, M Mogami, H., Samjeske, G. and Yamakata, A. (2008) Structure of water at the electrified platinum-water interface a study by surface-enhanced infrared absorption spectroscopy. J. Phys. Chem. C, 112, 4248- 256. 

Yamakata, A., Uchida, T., Kubota, J. and Osawa, M. (2006) Laser-induced potential jump at the electrochemical interface probed by picosecond time-resolved surface-enhanced infrared absorption spectroscopy./. Phys. Chem. B, 110, 6423-6427. 

Samjeske G, Miki A, Ye S, Osawa M. 2006. Mechanistic study of electrocatal3dic oxidation of formic acid at platinum in acidic solution by time-resolved surface-enhanced infrared absorption spectroscopy. J Phys Chem B 110 16559-16566. 

A related effect has been described for IR spectroscopy - Surface Enhanced Infrared Absorption spectroscopy (SEIRA). However, as the enhancement factors are significantly lower than for SERS and both the required metal particle size and the activation distance between the target molecule and the particle are more than one order of magnitude smaller, no practically applicable SEIRA sensors have been demonstrated up to now. 

We wondered why NSCs proliferated exclusively on surfaces with EGF-His ligands anchored by coordination. We focused on two aspects in particular the conformational integrity of coordinated EGF-His and the stability of coordinate bonds at the interface. Conformational information was acquired with multiple internal reflection-infrared absorption spectroscopy (MIR-IRAS) [97]. The stability of coordinate bonds was assessed by culturing NSCs on a surface with a small region of EGF-His ligands anchored by coordination. This spatially restricted EGF-His anchoring enabled an intuitive exploration of EGF-His release under cell culture conditions. 

As for silicon, secondary ion mass spectrometry (SIMS) is the most widely used profiling analysis technique for deuterium diffusion studies in III-V compounds. Deuterium advantageously replaces hydrogen for lowering the detection limit. The investigations of donor and acceptor neutralization effects have been usually performed through electrical measurements, low temperature photoluminescence, photothermal ionization spectroscopy (PTIS) and infrared absorption spectroscopy. These spectroscopic investigations will be treated in a separated part of this chapter. 

Infrared absorption spectroscopy is also a powerful tool for matrix isolation studies, which have been carried out extensively for alcohol clusters [34, 88, 103]. Recently, the gap between vacuum and matrix isolation techniques for direct absorption spectroscopy has been closed by the study of nano matrices that is, Ar-coated clusters of alcohols [80]. Furthermore, alcohol clusters can be isolated in liquid He nanodroplets, where metastable conformations may be trapped [160]. 

Nakanishi, K., Infrared Absorption Spectroscopy , 2nd ed., San Fransisco, Holden-Day, 1997. 

Any analytical method [312] suitable for determining equilibrium compositions of a reaction mixture at several temperatures can be used to obtain the enthalpy and the entropy of that reaction. The first example we describe involves a common analytical technique (infrared absorption spectroscopy) and addresses the energetics of the hydrogen bond between phenol and acetonitrile. This careful study on the equilibrium 14.6 was made by Sousa Lopes and Thompson more than 30 years ago [313]. 

The differently produced conductive polymer structures described above all have enhanced conductivity, which can be employed in microelectronics [44] and as sensors using immobilized enzymes [46, 47[. Martin and coworkers used polarized infrared absorption spectroscopy to access the alignment of the polymer fibers on the outer surface of the nanotubes [48[. The study showed that the enhancement of the conductivity is due to the alignment of the polymer fibers on the outer surface of the tubes. 

The mechanism of dissolution of the Cu UPD layer on Au(lll) has been studied by Ataka etal. [409]. The monolayer comprised Cu in 2/3 and sulfate in 1/3 proportions. It has been found by applying time-resolved surface-enhanced infrared absorption spectroscopy and chronoam-perometry that dissolution proceeds in two steps. In the first step, 1/3 Cu monolayer and all sulfate anions are removed via the Langmuir-type kinetics. In the second step, the rest of Cu is desorbed via nucleation and growth kinetics. 

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