Ultraviolet light spectroscopy

UHMWPE Ultrahigh-molecular-weight polyethylene (over 3 Mg mol ) ULDPE Ultralow-density polyethylene UV Ultraviolet light spectroscopy (irradiation)... 

Ultraviolet photoelectron spectroscopy (UPS) [2, 3 and 4, 6] differs from XPS in that UV light (He I, 21.2 eV He II, 40.8 eV) is used instead of x-rays. At these low excitmg energies, photoemission is limited to valence electrons. 

Ubichromenol synthesis, 3, 752 Ugi reaction, 5, 830 Uliginosin B, bromo-molecular dimensions, 3, 621 Ullman and Fetvadjian synthesis quinolines, 2, 477 Ullman synthesis acridines, 2, 470-benzacridines, 2, 470 Ultraviolet light absorbers in polymers, 1, 397-398 Ultraviolet spectroscopy heterocyclic compounds reviews, 1, 78... 

The widely used technique of light spectroscopy has also been applied to the qual and quant detn of bound N in energetic materials. There are five distinct systems used colorimetry, infrared spectroscopy, polarimetry, Raman spec troscopy and ultraviolet spectroscopy... 

Flame Photometry and Gas Chromatography (CyTerra) -Aerodynamic Particle Size and Shape Analysis (BIRAL) -Flow Cytometry (Luminex, LLNL) -Semiconductor-Based Ultraviolet Light (DARPA) -Polymer Fluorochrome (Echo Technology) -Laser-Induced Breakdown Spectroscopy -Raman Scattering -Infrared Absorption -Terahertz Spectroscopy -UV LIDAR... 

DNA is often present in amounts too small to be detected by direct spectroscopy. In this case, the fluorescent dye EtBr can be used to amplify the absorption. EtBr binds to the DNA molecule by intercalating between adjacent base pairs. It absorbs ultraviolet light at 300 nm and emits light at 590 nm in the red/orange region of the visible spectrum. The method can be used to determine the amount of DNA in a test-tube by comparing the EtBr-mediated fluorescence of the sample with that of standards of known amounts of DNA. 

The use of ultraviolet (UV) spectroscopy for on-line analysis is a relatively recent development. Previously, on-line analysis in the UV-visible (UV-vis) region of the electromagnetic spectrum was limited to visible light applications such as color measurement, or chemical concentration measurements made with filter photometers. Three advances of the past two decades have propelled UV spectroscopy into the realm of on-line measurement and opened up a variety of new applications for both on-line UV and visible spectroscopy. These advances are high-quality UV-grade optical fiber, sensitive and affordable array detectors, and chemometrics. 

Reduced forms of these coenzymes absorb ultraviolet light near 340 nm, whereas the oxidized forms do not. For NAD at neutral pH, the maximal absorbance band (s = 18000 M cm ) occurs at 260 nm another absorbance band (s = 8000 M cm ) occurs at 230 nm. For NADH, the maximal absorbance band (s = 16900 M cm ) occurs at 259 nm a second absorbance band (s = 6220 M cm ) occurs at 339 nm two weaker bands occur at 234 and 290 nm with respective s values of 6600 M cm and 1300 M cm h The same is true for NADP and NADPH at 339 nm. Occasionally, investigators have used thio-NADH which has a much stronger absorbance around 366 nm. See Absorption Spectroscopy (Fig. 4, pg. 5) Nicotinic Acid Analogs and Coenzymes... 

It is a remarkable fact that the contemporary history of absorption and emission spectroscopy began simultaneously, from the simultaneous discoveries that Bunsen and Kirchhoff made in the middle of the 19th century. They observed atomic emission and absorption lines whose wavelengths exactly coincided. Stokes and Kirchhoff applied this discovery to the explanation of the Fraunhofer spectra. Nearly at the same time approximately 150 years ago, Stokes explained the conversion of absorbed ultraviolet light into emitted blue light and introduced the term fluorescence. Apparently, the discovery of the Stokes shift marked the birth of luminescence as a science. 

In addition to ESR spectroscopy, which is a general method for detecting radicals, Dole et al. (9, 10, 11, 12) have developed a method of ultraviolet spectroscopy at low temperatures, which is specific for allylic and polyenylic radicals. Numerous papers have dealt with changes in polymers on irradiation, and all of these conclude that the reactions, in one way or another, arise from the formation of free radicals. Only a few papers describe experiments in which the radicals have been observed directly by ESR or ultraviolet spectroscopy at low temperatures. This article merely summarizes the present knowledge of the nature of radicals formed in polyolefins by irradiation in vacuum (ionizing radiation and ultraviolet light) and discusses some new trends in studying these radicals. 

One of the most startling developments in nmr spectroscopy since its inception has been the discovery of chemically induced dynamic nuclear polarization or CIDNP. An especially dramatic example is provided by irradiation of 3,3-dimethyl-2-butanone with ultraviolet light. 

Emulsion polymers and commercial controls were milled (Table III) and molded (Table IV) to produce test samples, and properties were evaluated following standard ASTM procedures (Tables V-VII). During accelerated ultraviolet light aging, the polymers were also examined by infrared spectroscopy of films cast from o-dichlorobenzene solution (Table VIII). 

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