Radiation monochromatic, production

The phenomenon of multiphoton dissociation finds a possible application in the separation of isotopes. For this purpose it is not only the high power of the laser that is important but the fact that it is highly monochromatic. This latter property makes it possible, in favourable circumstances, for the laser radiation to be absorbed selectively by a single isotopic molecular species. This species is then selectively dissociated resulting in isotopic enrichment both in the dissociation products and in the undissociated material. 

For the purposes of analytical chemistry, four kinds of monochromatic beams need to be considered. (The quotation marks are to remind the reader that the beams under discussion are not always truly monochromatic.) Three kinds of beams—those produced by Bragg reflection (4.9), filtered beams (4.6), beams in which characteristic lines predominate over a background that can be neglected— will be discussed later ( 6.2). The fourth kind of beam contains monochromatic x-rays that are a by-product of our atomic age and that promise to grow in importance they are given off by radioactive isotopes. These x-rays must not be confused with 7-rays (11.1), which also originate from radioactive atoms but which differ from x-rays because the transformation that leads to radiation involves the nucleus. 

Like many of the topics discussed in this book, photochemical reactions are most likely to be used in niche applications for commercial and environmental reasons. Unless there is a major breakthrough in reactor and lamp design, widespread use of this technology is unlikely. Perhaps the best hope of producing high-intensity monochromatic sources of radiation rests with lasers, but currently equipment costs are too high to justify their use for commercial chemical production. 

The ability to produce monochromatic radiation is a very desirable feature of photometric instruments because the Beer-Lambert relationship is only strictly true for monochromatic radiation. A good spectrophotometer may provide radiation of a specified wavelength with a range or bandwidth of as little as 0.1 nm, but it can be appreciated that even this is still not monochromatic when it is considered that the bandwidth of the sodium emission line is about 1 X 10-5 nm. This fact provides one of the major problems in the design of photometric instrumentation, namely the production of so-called monochromatic radiation. 

A quartz-free nontronite sample (6) was expanded by reacting a slurry containing 0.0075 g clay/g water with an excess of ChlorhydrolA pillared product was obtained that after drying at -100 C had a d(OOl) spacing of 19.4A. Calcination in air at 400 C/10h reduced the d(OOl) value to 16.9A the calcined ACH-Nontronite had BET surface area of 310 m /g and contained 31.9% FegOj. All powder diffraction measurements were obtained with a Siemens D-500 diffractometer at a scan of r/min using monochromatic Cu-Ka radiation. 

In practice a sample is irradiated with monochromatic radiation of wavelength Ar during a time t. The concentrations of reactants and products are determined by usual analytical methods. The second problem concerns the measurement of the number of photons absorbed. This is calculated from the number of photons incident on the sample, multiplied by the fraction of light absorbed x9... 

Hollaender, A. (1939). Wave-length dependence of the production of mutations in fungus spores by monochromatic ultra-violet radiation (2180-3650A). Proc. 7th. Int. Cong. Genetics 153-154. 

Folkard M, Prise KM, Vojnovic B, Brocklehurst B, Michael BD (2000) Critical energies for ssb and dsb induction in plasmid DNA by vacuum-UV photons an arrangement for irrdiating dry or hydrated DNA with monochromatic photons. Int J Radiat Biol 76 763-771 Folkard M, Prise KM, Turner CJ, Michael BD (2002) The production of single strand and double strand breaks in aqueous solution by vacuum UV photons below 10 eV. Radiat Prot Dosim 99 147-149 FoxRA, Fielden EM, SaporaO (1976) Yield of single-strand breaks in the DNA of E. coli 10 msec after irradiation. Int J Radiat Biol 29 391-394... 

The efficiency is found by dividing the electrical energy current by the incident energy current, given by the product of the incident (and absorbed) photon current and the photon energy huj, shown as the dashed rectangle in Fig. 4.4. The conversion efficiency for monochromatic solar radiation is shown in Fig. 4.5 as a function of the energy gap sq = hu. 

By using either a continuous or pulsed source of radiation and by measuring the amount of radiation absorbed by the reaction products, it is possible to determine product state distributions. The source of radiation can either be monochromatic (resonance lamp or laser) or broad-band (flash lamp or arc lamp) used in conjunction with a form of monochromator at the detector. The amount of absorption is monitored by an appropriate photosensitive or energy-sensitive detector. Particular care must be taken in the case of resonance lamps to avoid self-reversal of the output of the source, as this will complicate the quantitative analysis of product densities [17]. Similarly, laser sources must not be operated at such high output powers that the transitions involved become saturated, as this also complicates the analysis. Absorption measurements can be used for a wide range of reaction products, both ground and excited states of atoms, radicals and molecules [9,17, 22]. 

Procedures. Continuous irradiations of halocarbon solutions were conducted with monochromatic radiation in a merry-go-round apparatus (12) or in a Schoeffel reaction chemistry system. Reactions were followed through analysis for remaining halocarbon or analysis of chloride ions produced by the photoreactions. Dark controls were used in all cases to correct for thermal production of chloride ions. Ferrioxalate actinometers were used to determine the irradiance (16). The irradiance at the photoreaction cell surface was typically about 10 nanoeinsteins/cm2,s. The Fe(II) concentrations were determined by using a modified version of the ferrozine procedure described by Stookey (17). Electronic absorption spectra were obtained by using a Shi-madzu model 265 spectrophotometer. 

Valerophenone (277) serves as a reliable actinometer214 (Section 3.9.2) in quantum yield measurements when monochromatic radiation is used. Acetophenone (278), the type II product (Scheme 6.118), is formed in benzene with 0 — 033 (conditions 277 = 0-1 m Ain- nnm 20 °C).214,952 In contrast, the quantum yield of valerophenone consumption (type II elimination + Yang photocyclization) in water is close to unity (0 = 0.99 conditions 277 = 7 x 10 4m 2irr = 313nm 20°C).953... 

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