Polychromatic irradiation

Of particular interest are the photochemical investigations of the Cu(11)/ Mo(CN)g]4- mixed-valence system. Photochemical investigations have been performed by both monochromatic and polychromatic irradiations at selected energy regions. Low concentrations of octacyanomolybdatefIV) and copper(ll) have been used by reason of the low solubility of polymeric forms which are formed at higher concentrations. The analytical estimation of free cyanide has been used to monitor the photochemical reactions according to Scheme 3.. ... 

Table 3. The changes of melt enthalpy (AH ) and crystallinity in E-P copolymers in the solid state after polychromatic irradiation (>290nm) at 30 C...

Guerrero, M. A., andjones, R. D. (1996b). Photoinhibition of marine nitrifying bacteria. 2. Dark recovery after monochromatic or polychromatic irradiation. Marine Ecology-Progress Series 141, 193—198. 

N.S. Allen, A. Chirinos-Padron, and J.H. Appleyard, Photo-stabilizing action of metal chelates in polypropylene. Part I. Excited state quenching versus UV antioxidant action under polychromatic irradiation, Polym. Degrad. Stab. 1982, 4, 223-237. 

Palm, W. U. and Zetzsch, C., Investigation of the photochemistry and quantum yields of triazines using polychromatic irradiation and UV-spectroscopy as anal)4ical tool, Int J. Environ. Anal Chem., 65, 313-329, 1996. 

Singh et al. (112) studied the degradation behavior in air by ther-mogravimetry, differential thermal analysis and wide angle X-ray diffraction. It is observed that crystallinity and degradation were affected by thermal exposure and time of polychromatic irradiation. It was concluded that the processing of PCT must be done carefully, since it melts near its decomposition temperature. So, an exhaustive drying process at about 125 °C is commonly performed before its use (14). 

Figure 10.10 Cyclic voltammogram recorded under chopped illumination conditions. Polychromatic irradiation, the initial exposure time r = 20 min.

The method involves the irradiation of a sample with polychromatic X-rays (synchrotron radiation) which inter alia promote electrons from the innermost Is level of the sulfur atom to the lowest unoccupied molecular orbitals. In the present case these are the S-S antibonding ct -MOs. The intensity of the absorption lines resulting from these electronic excitations are proportional to the number of such bonds in the molecule. Therefore, the spectra of sulfur compounds show significant differences in the positions and/or the relative intensities of the absorption lines [215, 220, 221]. In principle, solid, liquid and gaseous samples can be measured. 

Films of purified PVCa were cast from methylene chloride solution on quartz plates. The solvent was allowed to slowly evaporate to give smooth, clear films with a thickness of ca. 5.0 nm. Contact angle measurements using water droplets were measured with a standard contact angle goniometer. Samples were photo-lysed in air with polychromatic light from a 150 watt xenon arc. Contact angles were measured after various times of irradiation to monitor the formation of oxidation products at the surface of the polymer films. 

Figure 3.14—Principle of the diode array detector. The flow cell is irradiated with a polychromatic UV/Vis light source. The light transmitted by the sample is dispersed by reflection on a grating and the reflected intensities are monitored by an array of photodiodes. Several hundred photodiodes can be used, each one monitoring the mean absorption of a narrow band of wavelengths (i.e. 1 nm).

Technically speaking, the sample is irradiated for a few microseconds with an intense pulse containing all frequencies included in the domain to be sampled. This can be compared to a polychromatic radiation source (like comparing a polychromatic to a monochromatic light source). For example, when working at 300 MHz, the frequency range has to be at least 6000 Hz in order to irradiate all the protons irrespective of their environment. Under these conditions, a small fraction of each type of proton (but not all the protons) will absorb the resonance frequency. 

Since in industrial photochemistry mostly polychromatic light sources are used, photon quantities are relatively difficult to calculate and require knowledge of the spectral distribution of the radiometric quantity measured. Assuming on the other hand that the radiometric measurements do not need to be corrected for the spectral response of the probe, the photon irradiance at a given point within the reactor volume would then be given by Eqs. (39) and (40), respectively. 

Benitez, F.J., Heredia, J.B., Gonzalez, T., and Real, F., Photooxidation of carbofuran by a polychromatic UV irradiation without and with hydrogen peroxide, Indust. Eng. Chem. Res., 34, 4099-4105,1995. 

The energy spectrum of constant angle, polychromatic coherent scatter may be transformed with the help of Eq. 3 into a diffraction profile depending on the momentum transfer, x, variable. The position of the active X-ray focus yields one spatial coordinate (y position) of the voxel irradiated for the 2-D scan data. This is complemented by the X voxel coordinate (= RP cos(0)) derived from the Z detector coordinate. The third spatial dimension of the scattering volume in the object under investigation in the Z direction is known from the position of the conveyor belt on which the object is translated and... 

The high production volume chemical, 4-chloro-2-methylphenol, XVI was photolysed in distilled and natural waters and aqueous solutions of soil-extracted humic substances (Ranker, Spain) under various irradiation conditions with monochromatic light at 280 nm, using polychromatic lamps emitting between 300 and 450 nm, and in natural sunlight (June, Clermont-Ferrand, France) [78,79]. 

The technology of UV disinfection of water and air is based on the direct irradiation of the media, mostly in homogeneous aqueous or gaseous phases. It is weU established in industry, and monochromatic LP or polychromatic MP mercury lamps as sources of UV-C radiation are apphed (cf. Schneider et al., 2001, Kalisvaart, 2001). 

In contrast, previous studies with LP Hg lamps indicated that a very high UV fluence Hq of up to 8000 mJ cm is required to inactivate Cryptosporidium. This observation was initially assigned to the much lower irradiance E of LP Hg lamps compared with that of MP Hg lamps or to wavelength effects (Bukhari et al, 1999). LP Hg lamps can be treated as being almost monochromatic UV-C sources ( max= 253.7 nm) whereas MP Hg lamps emit polychromatic radiation in the germicidal range between 200 and 300 nm (cf Fig.s 4-5 and 4-6). 

Alfano, O.M., Romero, R.L., and Cassano, A.E. A cylindrical photoreactor irradiated from the bottom. 111. Measurement of absolute values of the local volumetric rate of energy absorption. Experiments with polychromatic radiation . Chem. Eng. Sci. 41,1163 (1986). 

Under irradiation with polychromatic light at X > 300 nm and 60 °C, representative of outdoor exposures, polystyrene (PS) homopolymer, copolymers and blends do not directly absorb the incident radiation. It is well known that the photooxidation of these polymers results from light absorption by chromopho-ric impurities [1,2]. Photooxidation generates modifications of the chemical structure of the material, which results in the formation of oxidized groups, the development of discoloration and the loss of the initial mechanical properties. 

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