Optical absorption spectroscopy applications

GOME is a nadir sounding spectrometer which observes the up-welling radiance from the top of the atmosphere and the extra-terrestrial solar irradiance between 240 and 790 nm. The resolution of the measurements is chosen to be suitable for the application of the differential optical absorption spectroscopy (DOAS) technique, which was developed for long-path measurements and zenith sky observations (e.g. Platt and Pemer, 1980 Mounter a/., 1987 Eisinger etal., 1997). 

Note NA = not applicable FID = flame ionization detector DOAS = differential optical absorption spectroscopy. 

It would be beyond the scope of this article to attempt to explore all possible applications of alkenyl carbonium ions to catalytic reaction mechanisms. The several examples which have been discussed serve to illustrate the potential utility of optical absorption spectroscopy to problems in heterogeneous catalysis. 

Because of a low number density of cluster ions isolated in the gas phase, conventional methodologies available for condensed matters are not applicable to the measurements of the cluster properties. The first step of the measurements is to obtain a cluster ion with a desired size by mass-spectroscopic separation of cluster ions in a cluster source. After the size-selection, the number density of the size-selected cluster ion is typically 10 cm or lower, which is too low for the conventional optical absorption spectroscopy, for instance. In the measurement of an electronic conductivity, one should attach electrodes to the specimen that you intend to measure. 

Polystyrene. HREELS is usually applied in a qualitative way for the study of adsorbed molecules. The theoretical frame for these studies was established some 20 years ago [47]. However, its application to polymer surfaces is more recent [117, 118]. Polystyrene is a very common polymer and has been extensively studied in optical absorption spectroscopy and is often taken as a standard sample. It was extensively used as a standard sample to evidence the ability of HREELS to study polymeric surfaces, namely its quantitative capabilities. 

A variety of applications for optical absorption spectroscopy related to polymers has been proposed ... 

In low-dimensional systems, such as quantum-confined. semiconductors and conjugated polymers, the first step of optical absorption is the creation of bound electron-hole pairs, known as excitons [34). Charge photogcncration (CPG) occurs when excitons break into positive and negative carriers. This process is of essential importance both for the understanding of the fundamental physics of these materials and for applications in photovoltaic devices and photodctcctors. Since exciton dissociation can be affected by an external electric field, field-induced spectroscopy is a powerful tool for studying CPG. 

The potential applications of NIR OFCD determination of metal ions are numerous. The detection of metal contaminants can be accomplished in real-time by using a portable fiber optical metal sensor (OFMD). Metal probe applications developed in the laboratory can be directly transferred to portable environmental applications with minimal effort. The response time of the NIR probe is comparable to its visible counterparts and is much faster than the traditional methods of metal analysis such as atomic absorption spectroscopy, polarography, and ion chromatography. With the use of OFMD results can be monitored on-site resulting in a significant reduction in labor cost and analysis time. 

The luminescence of diamonds is related to various defects in its structure. Almost always, luminescence centers in diamonds are related to N atoms. It is logical, because the atomic radii of C and N are nearly equal (approximately 0.77 A). Luminescence spectroscopy has proven to be the most widely used method in studies of diamonds even in comparison with optical absorption, ESR, IR and Raman spectroscopies. Himdreds of spectra have been obtained, fluorescence characteristics enter into diamond quality gemological certificates, a wide range of electronic and laser applications are based on diamond optical properties in excited states nitrogen center aggregation is controlled by the residence time of diamond in the mantle, distinction between natural... 

The most frequently applied analytical methods used for characterizing bulk and layered systems (wafers and layers for microelectronics see the example in the schematic on the right-hand side) are summarized in Figure 9.4. Besides mass spectrometric techniques there are a multitude of alternative powerful analytical techniques for characterizing such multi-layered systems. The analytical methods used for determining trace and ultratrace elements in, for example, high purity materials for microelectronic applications include AAS (atomic absorption spectrometry), XRF (X-ray fluorescence analysis), ICP-OES (optical emission spectroscopy with inductively coupled plasma), NAA (neutron activation analysis) and others. For the characterization of layered systems or for the determination of surface contamination, XPS (X-ray photon electron spectroscopy), SEM-EDX (secondary electron microscopy combined with energy disperse X-ray analysis) and... 

Fourier transform methods have revolutionized many fields in physics and chemistry, and applications of the technique are to be found in such diverse areas as radio astronomy [52], nuclear magnetic resonance spectroscopy [53], mass spectroscopy [54], and optical absorption/emission spectroscopy from the far-infrared to the ultraviolet [55-57]. These applications are reviewed in several excellent sources [1, 54,58], and this section simply aims to describe the fundamental principles of FTIR spectroscopy. A more theoretical development of Fourier transform techniques is given in several texts [59-61], and the interested reader is referred to these for details. 

Electro-absorption (EA) spectroscopy, where optical absorption is observed under the application of an electric field to the sample, is another method that can distinguish between localised and inter-band excitations. The electric field produces a Stark shift of allowed optical absorptions and renders forbidden transitions allowed by mixing the wavefunctions of the excited states. Excitons show a quadratic Stark (Kerr) effect with a spectral profile that is the first derivative of the absorption spectrum for localised (Frenkel) excitons and the second derivative for charge transfer excitons, i.e. 

Tt may be safe to say that the interest of environmental scientists in airborne metals closely parallels our ability to measure these components. Before the advent of atomic absorption spectroscopy, the metal content of environmental samples was analyzed predominantly by wet or classical chemical methods and by optical emission spectroscopy in the larger analytical laboratories. Since the introduction of atomic absorption techniques in the late 1950s and the increased application of x-ray fluorescence analysis, airborne metals have been more easily and more accurately characterized at trace levels than previously possible by the older techniques. These analytical methods along with other modem techniques such as spark source mass spectrometry and activation analysis... 

It is not surprising therefore that the optical properties of small metal particles have received a considerable interest worldwide. Their large range of applications goes from surface sensitive spectroscopic analysis to catalysis and even photonics with microwave polarizers [9-15]. These developments have sparked a renewed interest in the optical characterization of metallic particle suspensions, often routinely carried out by transmission electron microscopy (TEM) and UV-visible photo-absorption spectroscopy. The recent observation of large SP enhancements of the non linear optical response from these particles, initially for third order processes and more recently for second order processes has also initiated a particular attention for non linear optical phenomena [16-18]. Furthermore, the paradox that second order processes should vanish at first order for perfectly spherical particles whereas experimentally large intensities were collected for supposedly near-spherical particle suspensions had to be resolved. It is the purpose of tire present review to describe the current picture on the problem. 

---