Ultraviolet light excitation

The effect of ultraviolet light on ethylene. Ultraviolet light excites one of the ethylene pi electrons into the antibonding orbital. The antibonding orbital is now occupied, so it is the new HOMO. ... 

This study attempts to identify the experimental parameters required to achieve the full-colored emission under accelerated electrons (cathode ray tube) and ultraviolet light excitations for ZnGa204 phosphor with graded and non-stoichiometric composition. 

Photolysis of aqueous soiutions of TNT, such as the wastes obtained from munition plants, leads to the formation of pink water. Ultraviolet light excites the nitro group to a triplet state according to the equation ... 

Photopolymerization and Plasma Polymerization. The use of ultraviolet light alone (14) as well as the use of electrically excited plasmas or glow discharges to generate monomers capable of undergoing VDP have been explored. The products of these two processes, called plasma polymers, continue to receive considerable scientific attention. Interest in these approaches is enhanced by the fact that the feedstock material from which the monomer capable of VDP is generated is often inexpensive and readily available. In spite of these widespread scientific efforts, however, commercial use of the technologies is quite limited. 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

Other techniques to inspect bonding surfaces for contamination have also been proposed, including ultraviolet fluorescence [162], Pulsed ultraviolet light incident on the surface excites fluorescence of organic contamination, which can... 

Instruments for the measurement of fluorescence are known as fluorimeters or spectrofluorimeters. The essential parts of a simple fluorimeter are shown in Fig. 18.1. The light from a mercury-vapour lamp (or other source of ultraviolet light) is passed through a condensing lens, a primary filter (to permit the light band required for excitation to pass), a sample container, a secondary filter (selected to absorb the primary radiant energy but transmit the fluorescent... 

Franck and Gustav Hertz passed electrons through mercury vapor at low pressure to determine the minimum kinetic energy required to produce the excited state that emits ultraviolet light at 253.7 nm. What is that minimum kinetic energy What wavelength is associated with electrons of this energy ... 

Purines absorb only ultraviolet light and they contribute to structural colors (white and silver) in animals. Pterines are generally yellow, orange, or red pigments. Because they are amphoteric molecules, the absorption spectra depend on the pH and present three or two absorption maxima, usually one in the visible region. Sepiapterin has an absorption maximum at 340 nm in O.IM NaOH and at 410 nm in O.IM HCl." Leucopterin has three maxima 240, 285, and 340 nm. Xanthopterin has two 255 and 391 nm. Because they are conjugated with proteins, pterins show bathochromic shifts in vivo. They also present fluorescence when excited with UV light. 

The absorption of visible light of a particular frequency by atoms or molecules of a solute is perceived by our eyes as the color of this substance. Hence, only colored substances—natural or synthetic dyes— are excited by visible light. Under ultraviolet light, substances not absorbing in the visible part of the spectrum can also be... 

When molecules react thermally, at room temperature or on heating, they are in their lowest electronic states. However, when reactions occur on irradiation of the molecules with visible or ultraviolet light, the processes involve species in electronic excited states. Some of the details of such processes are known, but there is still much to do. Since photoexcitation is important in many areas— photosynthesis, photography, electronic displays, solar cells, cancer-causing ul-... 

An electron in the circle is called the excited electron. Absorption, although at a longer wave length than saturated hydrocarbons occurs below 9.4 x 101 K cal/mole. Therefore, ethers, disulphides, alkyl halides and alkyl amines are transparent to ultraviolet light. 

The quantised energy levels of matter have a separation that is of the same order as the energy of visible or ultraviolet light. Thus the absorption of visible or ultraviolet light by matter can excite electrons to higher energy levels, producing electronically-excited species. 

In 2000, most European countries switched from their traditional currencies to the euro. Lanthanide luminescence is used as a means of preventing counterfeit euro banknotes from passing into the money chain. Excitation of euro banknotes with ultraviolet light results in fluorescence in the red, green and blue regions due to complexes of europium (Eu3+), terbium (Tb3+) and thulium (Tm3+), respectively, that are present in the banknotes. 

When a molecule absorbs a quantum of light, it is promoted to an excited state. Because the energy of visible and ultraviolet light is of the same order of magnitude as that of covalent bonds, another possibility is that the molecule may cleave into two parts, a process known as photolysis. 

Photochemistry is the branch of chemistry which relates to the interactions between matter and photons of visible or ultraviolet light and the subsequent physical and chemical processes which occur from the electronically excited state formed by photon absorption. 

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