Reflection-absorption spectroscopy examples

The ILs interact with surfaces and electrodes [23-25], and many more studies have been done that what we can cite. As one example, in situ Fourier-transform infrared reflection absorption spectroscopy (FT-IRAS) has been utilized to study the molecular structure of the electrified interphase between a l-ethyl-3-methylimidazolium tetrafluoroborate [C2Qlm][BF4] liquid and gold substrates [26]. Similar results have been obtained by surface-enhanced Raman scattering (SERS) for [C4Cilm][PFg] adsorbed on silver [24,27] and quartz [28]. 

Many similar studies have been done at surface science conditions using step-function concentration signals. For example, Takagi et al. (52) studied the adsorption and desorption of CO on Ni(lOO) via infrared reflection absorption spectroscopy (IRAS). In one case, CO dosing was turned on for 214 s and then turned off. The response of the spectrum of the surface intermediate was followed by IRAS. Of course, under these high-vacuum... 

The third example is the reflection measurement at a rotating disk electrode (RDE). Scherson and his coworkers have developed near-normal incidence UV-visible reflection-absorption spectroscopy at RDEs [50-52]. Both (AR/R)dc and (AR/R)er have been measured under hydrodynamic conditions. The use of an RDE enables them to quantitatively control the diffusion layer concentration profile of the solution phase species, especially the species generated electro-... 

Whereas ATR spectroscopy is most commonly applied in obtaining infrared absorption spectra of opaque materials, reflection-absorption infrared spectroscopy (RAIRS) is usually used to obtain the absorption spectrum of a thin layer of material adsorbed on an opaque metal surface. An example would be carbon monoxide adsorbed on copper. The metal surface may be either in the form of a film or, of greaf imporfance in fhe sfudy of cafalysfs, one of fhe parficular crysfal faces of fhe mefal. 

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

Figure 8.7. Delayed fluorescence and diffuse reflectance transient absorption spectroscopy on scattering substrates. Example terthicnyl on silica gel excited with = 354 nm (neodymium/yttrium-aluminum-garnet) (Nd/YAG) laser pulse of 10 nsec, 20 mj), recorded with a gated diode array spectrometer.

The empirical modeling element indicates an increased emphasis on data-driven rather than theory-driven modeling of data. This is not to say that appropriate theories and prior chemical knowledge are ignored in chemometrics, but that they are not relied upon completely to model the data. In fact, when one builds a chemometric calibration model for a process analyzer, one is likely to use prior knowledge or theoretical relations of some sort regarding the chemistry of the sample or the physics of the analyzer. For example, in process analytical chemistry (PAC) applications involving absorption spectroscopy, the Beer s Law relation of absorbance vs. concentration is often assumed to be true and in reflectance spectroscopy, the Kubelka-Munk or log(l/P) relations are assumed to be true. 

Extending the equipment, the authors (Beale et al., 2005) recently added energy dispersive X-ray absorption spectroscopy (XAS). Raman and UV-vis spectra are recorded by illuminating opposite sides of a catalyst bed in a vertical tubular reactor and detecting the scattered and reflected light as described above. XAS is performed in the same horizontal plane but in transmission and with the beam orthogonal to the incident radiation of the other two methods. Example spectra were recorded for samples at 823 K. A combination of UV-vis (fiber optics) and XAFS spectroscopy for investigation of solids has also been described by Jentoft et al. (2004), who reported UV-vis measurements of samples at 773 K. 

For information on the analysis of surfaces by IR radiation instead of electrons, a complimentary technique known as reflection absorption infrared spectroscopy (RAIRS), see (a) http //www.uksaf.org/tech/rairs.html (b)http //www.cem.msu.edu/ cem924sg/Topicll.pdf For example, the development of fibers/fabrics that will actively adsorb and surface deactivate chemical and biological warfare agents — of increasing importance as new modes of terrorist activity continue to emerge. For more information, see (a) http //web.mit.edu/isn/(Institute of Soldier Nanotechnologies at M.I.T.). (b) Richards, V. N. Vohs, J. K. Williams, G. L. Fahlman, B. D. J. Am. Ceram. Soc. 2005,88,1973. 

When the sample is stimulated hy application of an external electromagnetic radiation source, several processes are possible. For example, the radiation can be scattered or reflected. What is important to us is that some of the incident radiation can be absorbed and thus promote some of the analyte species to an excited state, as shown in Figure 24-5. In absorption spectroscopy, we measure the amount of light absorbed as a function of wavelength. This can give both qualitative and quantitative information about the sample. In photoluminescence spectroscopy (Figure 24-6), the emission of photons is measured after absorption. The most important forms of photoluminescence for analytical purposes are fluorescence and phosphorescence spectroscopy. 

---