Ultra violet

It is the simplest compound containing the -N = N- chromophore, but is of no practical importance since it lacks affinity for fibres. Normally it exists in the most stable trans form, but may be converted to a less stable, bright red as form, m.p. 71 -S C by ultra-violet irradiation. Cis to irans isomerization occurs rapidly on heating. [Pg.48]

BHC is manufactured by chlorination of benzene in the presence of ultra-violet light. The gamma-isomer is obtained from the crude mixture by selective crystallization, and forms colourless crystals, m.p. I13" C. U.S. production 1980 400 tonnes. [Pg.59]

Use of Ultra Violet Spectrometty to Obtain Distribution by Hydrocarbon Families... [Pg.53]

In the electromagnetic spectrum, the ultra violet region is between that of X-rays and visible light. This corresponds to the energies hv ot one hundred to a few tens of electron-volts (wavelengths from 180 to 400 nm). [Pg.53]

Ozone, O3, is found in trace quantities in the upper atmosphere where it is believed to be formed by the photochemical dissociation of oxygen molecules by the intense ultra-violet light from the sun ... [Pg.262]

Purification of anthracene. Dissolve 0-3 g. of crude anthracene (usually yellowish in colour) in 160-200 ml. of hexane, and pass the solution through a column of activated alumina (1 5-2 X 8-10 cm.). Develop the chromatogram with 100 ml. of hexane. Examine the column in the hght of an ultra-violet lamp. A narrow, deep blue fluorescent zone (due to carbazole, m.p. 238°) will be seen near the top of the column. Immediately below this there is a yellow, non-fluorescent zone, due to naphthacene (m.p. 337°). The anthracene forms a broad, blue-violet fluorescent zone in the lower part of the column. Continue the development with hexane until fluorescent material commences to pass into the filtrate. Reject the first runnings which contain soluble impurities and yield a paraffin-hke substance upon evaporation. Now elute the column with hexane-benzene (1 1) until the yellow zone reaches the bottom region of the column. Upon concentration of the filtrate, pure anthracene, m.p. 215-216°, which is fluorescent in dayhght, is obtained. The experiment may be repeated several times in order to obtain a moderate quantity of material. [Pg.944]

Braude, Ultra-Violet Light Absorption and the Structure of Organic Compounds Annual Reports, 42, 105 (1945). ... [Pg.1150]

Experimental information about tire energy levels of molecules is obtained from spectroscopic studies, in the infra-red for the rotational states and in the ultra-violet for die vibrational and most of the dissociation energies. Some thermodynamic data are also obtained for the dissociation energies using mass spectroscopy. [Pg.45]

There are therefore two ways in which lasers may be used to bring about photon-assisted film formation. If the laser emits radiation in the near-ultra-violet or above, photochemical decomposition occurs in the gas phase and some unabsorbed radiation arrives at the substrate, but this latter should be a minor effect in die thin film formation. This procedure is referred to as photolysis. Alternatively, if the laser emits radiation in the infra-red, and tire photons are only feebly absorbed to raise the rotational energy levels of the gaseous... [Pg.82]

Turning to non-metallic catalysts, photoluminescence studies of alkaline-earth oxides in dre near-ultra-violet region show excitation of electrons corresponding to duee types of surface sites for the oxide ions which dominate the surface sUmcture. These sites can be described as having different cation co-ordination, which is normally six in the bulk, depending on the surface location. Ions on a flat surface have a co-ordination number of 5 (denoted 5c), those on the edges 4 (4c), and dre kiirk sites have co-ordination number 3 (3c). The latter can be expected to have higher chemical reactivity than 4c and 5c sites, as was postulated for dre evaporation mechanism. [Pg.124]

Since acetal resins are degraded by ultra violet light, additives may be included to improve the resistance of the polymer. Carbon black is effective but as in the case of polyethylene it must be well dispersed in the polymer. The finer the particle size the better the ultra violet stability of the polymer but the poorer the heat stability. About 1.5% is generally recommended. For white compounds and those with pastel colours titanium dioxide is as good in polyacetals as most transparent ultraviolet absorbers, such as the benzophenone derivatives and other materials discussed in Chapter 7. Such ultraviolet absorbers may be used for compounds that are neither black, white nor pastel shade in colour. [Pg.543]

Detection limits for various elements by TXRF on Si wafers are shown in Fig. 4.13. Synchrotron radiation (SR) enables bright and horizontally polarized X-ray excitation of narrow collimation that reduces the Compton scatter of silicon. Recent developments in the field of SR-TXRF and extreme ultra violet (EUV) lithography nurture our hope for improved sensitivity down to the range of less than 10 atoms cm ... [Pg.190]

OZONE A reactive form of oxygen the molecule of which contains 3 atoms of oxygen. In the ozone layer it protects the earth by filtering out ultra-violet rays. At ground level, as a constituent of photochemical smog, it is an imtant and can cause breathing difficulties. [Pg.16]

OZONE LAYER A thin layer of ozone that lies about 25 kilometres above the earth in the stratosphere. Forms a protective screen against harmful radiation by filtering out ultra-violet rays from the sun. [Pg.16]

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