Ultraviolet—visible absorption spectroscopy

CdS nanocrystallites of various sizes 6.0, 4.5 and 2.2 nm diameters. The bulk spectra for the two systems are also shown. Adapted from [11, 99, 100]. 

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Low-temperature, photoaggregation techniques employing ultraviolet-visible absorption spectroscopy have also been used to evaluate extinction coefficients relative to silver atoms for diatomic and triatomic silver in Ar and Kr matrices at 10-12 K 149). Such data are of fundamental importance in quantitative studies of the chemistry and photochemistry of metal-atom clusters and in the analysis of metal-atom recombination-kinetics. In essence, simple, mass-balance considerations in a photoaggregation experiment lead to the following expression, which relates the decrease in an atomic absorption to increases in diatomic and triatomic absorptions in terms of the appropriate extinction coefficients. 

MOLECULAR SPECTROSCOPY 4.35.3.1 Ultraviolet-Visible Absorption Spectroscopy... 

Dioctadecylamino-l,3,5-Triazine AmphiphUe at the Air-Water Interface Studies by Ultraviolet-Visible Absorption Spectroscopy and Brewster Angle Microscopy , Langmuir, 14,2174(1998)... 

As already pointed out, the most direct consequence of a reduction in the nanocrystallite size on the electronic structure of semiconducting materials is a pronounced increase in the band gap due to the quantum confinement effect. While there are several ways to quantitatively understand this phenomenon from a theoretical standpoint, the experimental determination of the band gap variation as a function of size is most directly performed by ultraviolet-visible absorption spectroscopy, with the experimental absorption threshold corresponding to the direct band gap in the material. As the band gap shifts to higher energy, the blue-shift in the absorption edge signals the formation of progressively smaller sized nanocrystals. Therefore, UV-Vis absorption spectroscopy has played an immensely important role in the study of these systems and we discuss the essential aspects in Section 11.3. 

Molecular spectroscopy based on ultraviolet, visible, and infrared radiation is widely used for the identification and detennination of many inorganic, organic, and biochemical species. Molecular ultraviolet/visible absorption spectroscopy is used primcirily for quantitative analysis and is probably more extensively applied in chemical and clinical laboratories throughout the world than any other single method. Infrared absorption spectroscopy is a poweiful too for determining the structure of both inorganic and organic compounds. In addition, it now plays an important role in quantitative analysis, particularly in the area of environmental pollution. 

The ultraviolet-visible method is useful for the study of electronic transitions in molecules and atoms. Although various forms of ultraviolet-visible spectroscopy can be used to study a myriad of important chemical and physical properties, we will be most concerned with its use in quantitative analysis. It is probably the single most frequently used analytical method, with the possible exception of the analytical balance. For example, a single clinical analysis laboratory in a major hospital may perform a million chemical analyses a year, primarily on serum and urine, and about 707o of these tests are done by ultraviolet-visible absorption spectroscopy. Atomic absorption and emission spectroscopy (Chaps. 10 and 11) is used primarily to analyze for metallic elements in a variety of matrices—serum, natural waters, tissues, and so forth. 

Absorption spectroscopy technologies use particular parts of the electromagnetic (EM) spectra. The sample s absorption of the EM waves reveals its molecular make-up. Examples of this type include atomic absorption spectroscopy, ultraviolet/visible absorption spectroscopy, and infrared spectroscopy. 

Thompson C. Ultraviolet-Visible Absorption Spectroscopy. Willard Grant Press, 1974, Chaps. 2 and 3. 

A The Magnitude of Molar Absorptivitics 367 14B Absorbing Species 367 14C Qualitative Applications of Ultraviolet-Visible Absorption Spectroscopy 372... 

Tomita, S., Hayashi, S., Tsukuda, Y, Fujii, M., 2002b, Ultraviolet-visible absorption spectroscopy of carbon onions, Phys. Solid State 44,450-453. 

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