Light polychromatic

No account of UV detectors would be complete without mention of the diode array (multichannel) detector, in which polychromatic light is passed through the flow cell. The emerging radiation is diffracted by a grating and then falls on to an array of photodiodes, each photodiode receiving a different narrow-wavelength band. A microprocessor scans the array of diodes many times a... 

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. 

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. 

The photodegradation of 12 polycyclic aromatic hydrocarbons (PAHs) in pure water, in solutions of Suwannee River fulvic acid (5 mg L-1) and in natural waters under polychromatic light (X > 290 nm) was investigated [64],... 

This is a tungsten polychromatic light source producing light in the spectral range 320-2500 nm. It is essential that the power supply is perfectly stable to ensure constant light intensity. 

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. 

Irradiation of ABS under polychromatic light in the presence of atmospheric oxygen leads to noticeable evolutions of the UV and FTIR spectra of exposed films. 

The determination of photochemical quantum yields is not a simple task, and, in some cases, approximations are required. Nevertheless, according to the parameters chosen, various well-known photochemical reactions can be used to measure irradiance, which is an essential quantity in the field of photokinetics. Finally, some selected chemical actinometers will be discussed with respect to their pros and cons and their best areas of application. At the end, special applications of actinometry such as measurements of polychromatic light and high-intensity light sources (lasers) will be described. The overall aim of this chapter is to help the reader to choose the best actinometers out of the numerous examples in the literature and avoid technical mistakes. 

The actinometers described in the section "Selected Chemical Actinometers" are mostly used to measure the intensity of monochromatic radiation emitted by conventional sources, such as mercury or xenon arc lamps, metal halide lamps, etc. In this section, special applications of chemical actinometer will be reviewed, including the measurement of intensities of lasers and polychromatic light sources. In addition. 

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