Ultraviolet-visible spectroscop

Moving an electron from a ground state to an excited state (Eeiectronic)> leading to observations in the ultraviolet-visible spectroscopic region... 

Harder, J. W., A. Fried, S. Sewell, and B. Henry, Comparison of Tunable Diode Laser and Long-Path Ultraviolet-Visible Spectroscopic Measurements of Ambient Formaldehyde Concentrations during the 1993 OH Photochemistry Experiment, . /. Geophys. Res., 102, 6267-6282 (1997b). 

Mangrich, A. S., Lermen, A. W., Santos, E. J., Gomes, R. C., Coelho, R. R. R., Linhares, L. F., and Senesi, N. (1998). Electron paramagnetic resonace and ultraviolet-visible spectroscopic evidence for copper porphyrin presence in actinomycete melanims from soils. Biol. Fertil. Soils 26, 341-345. 

Other semiempirical Hamiltonians have also been used within the BKO model. A Complete Neglect of Differential Overlap (CNDO/2) ° study of the effect of solvation on hydrogen bonds has appeared. o The Intermediate Neglect of Differential Overlap (INDO) °2 formalism has also been employed for this purpose.2011 Finally, the INDO/S model,which is specifically parameterized to reproduce excited state spectroscopic data, has been used within the SCRF model to explain solvation effects on electronic spectra.222,310-312 jhis last approach is a bit less intuitively straightforward, insofar as the INDO/S parameters themselves include solvation by virtue of being fit to many solution ultraviolet/visible spectroscopic data.29J... 

Liu, S.-Q., Cao, M.-L., and Dong S.-L., 2008. Electrochemical and ultraviolet-visible spectroscopic studies on the interaction of deoxyribonucleic acid with vitamin Bg. Bioelectrochemistry. 74 164-169. 

Van der Waals complexes can be observed spectroscopically by a variety of different teclmiques, including microwave, infrared and ultraviolet/visible spectroscopy. Their existence is perhaps the simplest and most direct demonstration that there are attractive forces between stable molecules. Indeed the spectroscopic properties of Van der Waals complexes provide one of the most detailed sources of infonnation available on intennolecular forces, especially in the region around the potential minimum. The measured rotational constants of Van der Waals complexes provide infonnation on intennolecular distances and orientations, and the frequencies of bending and stretching vibrations provide infonnation on how easily the complex can be distorted from its equilibrium confonnation. In favourable cases, the whole of the potential well can be mapped out from spectroscopic data. 

The focus of this chapter is photon spectroscopy, using ultraviolet, visible, and infrared radiation. Because these techniques use a common set of optical devices for dispersing and focusing the radiation, they often are identified as optical spectroscopies. For convenience we will usually use the simpler term spectroscopy in place of photon spectroscopy or optical spectroscopy however, it should be understood that we are considering only a limited part of a much broader area of analytical methods. Before we examine specific spectroscopic methods, however, we first review the properties of electromagnetic radiation. 

Transitions between different electronic states result in absorption of energy in the ultraviolet, visible and, for many transition metal complexes, the near infrared region of the electromagnetic spectrum. Spectroscopic methods that probe these electronic transitions can, in favourable conditions, provide detailed information on the electronic and magnetic properties of both the metal ion and its ligands. 

For ultraviolet and visible spectroscopic detectors, a standard solution of a compound whose molar absorption constant is known must be prepared, and placed in the flow cell. The absorbance obtained is then compared with the value measured by a standard spectrophotometer. 

A number of methods used to decide which type of cation is formed rely upon spectroscopic comparisons of protonated molecules with the methylation or alkylation products in general ([3] and [4], with Me or R instead of H). In alkylation products there is no mobility of the group R and the structure of the ion is thus fixed. There is no possibility of mobile tautomeric equilibria. The properties of the TT-electron system, which determines nmr coupling constants and ultraviolet/visible absorption (and, not quite... 

There have been relatively little ultraviolet-visible (UV-Vis) spectroscopic data for 1,4-oxazines, but selected data are presented in Table 8. UV spectroscopy is important for photochromic compounds, such as spirooxazines. The UV spectra of 33 spirooxazines in five different solvents are collected in a review <2002RCR893>, and the more recently reported examples of photochromic oxazines 65, 66, 101, and 102 are shown here. It can be seen from Table 8 that both adding methoxy substituents to the oxazine and changing to a more polar solvent give a UV maximum at a higher wavelength. This solvent effect can also be seen in the case of 102, which also has important fluorescence properties, discussed in Section 8.06.12.2. 

Whether laser flash photolysis (LFP) is used to detect RIs before they react, or matrix isolation at very low temperatures is employed to slow down or quench these reactions, spectroscopic characterization of RIs is frequently limited to infrared (IR) and/or ultraviolet-visible (UV-vis) spectroscopy. Nuclear magnetic resonance (NMR) spectroscopy, which is generally the most useful spectroscopic technique for unequivocally assigning structures to stable organic molecules, is inapplicable to many types of RI. 

Like diffraction, spectroscopic methods using ultraviolet, visible, or infrared light are generally much Easier than molecular vibrations or interconversions, and the... 

Post-column detection of chlorophyll derivatives is often accomplished by ultraviolet and visible spectroscopic techniques, which take advantage of the strong electronic absorption spectra of these pigments (units F4.3 F4.4). While these methods have enjoyed wide application (Schwartz et al., 1981 Khachik et al., 1986), a major advance was made with the introduction of photodiode array (PDA) detection. Multichannel photodiode array detection allows for simultaneous monitoring of multiple wavelengths, resulting in the generation of online electronic absorption spectra of a compound as it elutes from the HPLC column. Because of the uniqueness of electronic absorption spectra of individual chlorophyll derivatives, these techniques have enjoyed extensive application for tentative identification of components from complex mixtures and extracts... 

The tautomerism of 4 (Figure 1) was also studied by UV-Vis (ultraviolet-visible) spectroscopy in polar aprotic solvents the effect of added water, darkness, and indirect sunlight were also evaluated. The experimental spectroscopic results are discussed in Section 13.14.3.1.1 (i). Theoretical calculations using ZINDO/S were performed to state the allowed absorption transitions <2005SAA875>. The five tautomeric structures of 4 as well as the calculated energies for each are depicted in Figure 2. 

Aromatic compounds. These compounds exhibit characteristic absorption in the ultraviolet-visible region of the spectrum, and although they are frequently easily recognised from their other spectroscopic properties, examination of their electronic spectra can often lead to the elucidation or confirmation of some of the detailed structural features. 

Collections of spectroscopic data (a) Standard Spectra Collection. Sadtler Research Laboratories, Philadelphia. (The 1980 index covers 48 000 grating i.r. spectra, 59000 prism i.r. spectra, 48 000 ultraviolet/visible spectra, 32 000 60 MHz n.m.r. spectra, and 7000 carbon-13 n.m.r. spectra.)... 

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