Absorption of Ultraviolet Light

Technology has been introduced for on-line estimation of the kappa number based on absorption of ultraviolet light (35). This breakthrough ia optical sensor technology permits closed-loop feedback control of digesters from on-line measurement of the kappa number. 

Apart from this gravitational effect, there are composition changes due to chemical reactions induced by light. These are caused by absorption of ultraviolet light in the upper atmosphere. For example, oxygen absorbs ultraviolet light and the energy taken up by the molecule exceeds the... 

Alternatively, upon absorption of ultraviolet light, a photochemical reaction can occur—that is, a reaction triggered by the energy provided from light. This reaction destroys the hypochlorite ion and produces chloride ion and oxygen gas, which escapes from the pool ... 

Note that since the atomic chlorine consumed in reaction 8.5 is regenerated in 8.7, it acts as a catalyst for ozone decomposition. Reaction 8.6 represents the decomposition of ozone by ultraviolet light, so that reactions 8.6 and 8.2 form a dynamic system that accounts for the absorption of ultraviolet light by the ozone layer. 

FIGURE 3-6 Absorption of ultraviolet light by aromatic amino acids. 

Nylons require modification or stabilization to improve their resistance to certain environmental effects. Unstabilized nylon is degraded by ultraviolet light. The most widely used stabilizer has been approximately 2% well-dispersed carbon black, which has proved effective in the absorption of ultraviolet light. The nylons are considered adequate for outdoor applications if they are not exposed to direct sun-hght,... 

Tyrosine is one of the important a-amino acids and is oxidatively polymerized with tyrosinase to melanin, the black pigment in animals [25-30], Melanin plays a role in the prevention of damage to the organism that occurs through the absorption of ultraviolet light. Melanin is the only major paramagnetic organic com-... 

There are four modes of action important in stabilizing polypropylene (1) free radical scavenging (2) decomposition of peroxides (3) regeneration of inhibitors in synergistic antioxidant systems (4) absorption of ultraviolet light and re-emission of absorbed energy in nondegrading forms. 

Photostabilization with Ultraviolet Absorbers. Absorption of ultraviolet light in the region 2900-3900 A. (290-390 m/x) results in the yellowing and loss in physical-mechanical properties of most polymers containing aliphatic C—H bonds. This degradation is usually a combination of ultraviolet absorption and oxidative attack (21). 

Ozone is an extremely reactive chemical. Its reaction with alkenes was discussed in Section 11.11. Although it is considered a pollutant in the lower atmosphere, its presence in the upper atmosphere has beneficial health effects due to its absorption of ultraviolet light. 

Know the names, structures, and classification of all amino acids and their side chains present in proteins, and be familiar with their physical and chemical properties, such as conformation, absorption of ultraviolet light, and reactions with ninhydrin. 

The most common reaction of carbonyl complexes is CO dissociation. This reaction, which may be initiated thermally or by absorption of ultraviolet light, characteristically involves loss of CO from an 18-electron complex to give a 16-electron intermediate, which may react in a variety of ways, depending on the nature of the complex and its environment. A common reaction is replacement of the lost CO by another ligand to form a new 18-electron species as product. For example,... 

The principle of operation of the PID is photoionisation. The absorption of ultraviolet light by a molecule leads to ionisation of the molecule ... 

Does the absorption of ultraviolet light by cyclohexene occur at longer or at shorter wavelengths than the absorption hy benzene Explain. 

The absorption of ultraviolet light by proteins at wavelength 280 nm is caused mostly by the amino acids tyrosine and tryptophan along the protein molecular chains. The molecular absorption coefficients for these two amino acids are ... 

Absorption of ultraviolet light (254 nm). For determination of benzodiazepines, barbiturates, and methaqualone. 

Direct photochemical degradation of 1,1,1-trichloroethane in the troposphere is not expected to be an important fate process, because there is no chromophore for absorption of ultraviolet light (>290 nm) found in sunlight at tropospheric altitudes (Hubrich and Stuhl 1980 VanLaethem-Meuree et al. 1979). A laboratory experiment performed in sealed Pyrex ampules showed loss of 1,1,1-trichloroethane in 2 weeks under the influence of sunlight however, catalysis by the Pyrex surface was probably responsible for the enhanced reactivity (Buchardt and Manscher 1978). 

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