Energy sinks

Example 8 Ejfective Gas Emissivity Methane is hiimed to completion with 20 percent excess air (air half-saturated with water vapor at 298 K (60 F), 0.0088 mols H20/mol dry air) in a furnace chamber of floor dimensions. 3 X 10 m and heights m. The whole surface is a gray-energy sink of emissivity 0.8... 

Since icosahedral carboranes are generally viewed as 3D energy sinks as well as polymer building blocks, the thermal and radiation stability that these units impart on the base rubbery material needs to be explored. While the thermal stability of these materials has been studied and reported by a number of workers, there is little reported work on the stability of these materials to ionizing radiation. A brief account of our work within this area is detailed below. 

A carbonyl chromophore in a macromolecule can participate in a variety of photochemical processes that can have as end result the degradation of the polymer via processes like the Norrish Type I or Type II reaction, the triggering of a chain reaction leading to peroxidation, the transfer of energy to another chromophore or, it can also behave as an energy sink if a suitable, non-degradative path, is available to the triplet state. 

Another common hydrogen transfer reaction of carbonyl triplet is the photoenolization of the c-methylbenzoyl chromophore, illustrated in reaction 3 for the syn conformer of c-methylaceto-phenone (j+). Reaction 3 can act as a very efficient energy sink, and a number of properties of this group led us to believe that this process could be used to reduce photodegradation i.e. the excellent absorption characteristics of the chromophore, the short triplet lifetime and the fact that the disappearance of the carbonyl triplet does not take place at the expense of the formation of another excited state. 

In some condensation reactions the product is attained only by way of rather implausible looking intermediates of high energy. The stable product represents a free energy sink that drains off the high energy... 

In the radiative transition shown, most of the energy is removed from the system by photon emission, whereas for the radiationless transition the sum of the electronic energy and vibrational energy is constant and energy is subsequently removed from the system by vibrational relaxation to v = 0 of f2, with the solvent acting as an energy sink. 

Debye s investigations on the energy content of substances at low temperatures be expressible in the form u — Uq aT , where a is determinable from the heat capacity of the surface film, and the temperature coefficient of the heat of wetting should decrease rapidly as we approach the absolute zero. Furthermore it is evident that at this temperature the free and total surface energies should be identical in value, the total surface energy sinking first slowly and then rapidly as the critical temperature is reached. Confirmation likewise of the assumption Lt = 0 or that the temperature... 

For the benzene derivatives here considered no dissociated methyl or amino radicals could be found in the mass spectra, either under the action of the photons alone, or in conjunction with a bombardment with slow electrons. As mentioned above this method of combined excitation has been attempted for the detection of neutral radicals produced under illumination.26 The fact that no such radicals have been detected for the compounds studied here, would mean, as generally assumed, that the benzene ring is an efficient energy sink, degrading the excess of vibrational energy imparted by the photon to the linkage between the substituent and ring. 

The latter reaction is widely used as a proving ground for new theories. Particles B (called also scavengers) are unsaturable energy sinks and thus after rapid light emission can absorb it anew. In this case the reaction scheme is A + B —> B (concentration of B s remains constant raB) which could be described by the following kinetic equation... 

The photochemical properties of 9-styrylanthracenes 70/71, all of them substituted by polar groups in the 10-position of the anthracene, closely resemble those of the parent compounds 68a/69a insofar as trans->cis isomerization is either nondetectable or inefficient in both cyclohexane and acetonitrile solution (see Table 11). The lack of photochemical trans-+cis isomerization of the 10-formyl and benzoyl derivatives 71b, 71c and 71d is of particular interest in view of the substituent effect which both the benzoyl and formyl groups exert on the photochemical trans- cis isomerization of 9-styrylanthracenes 69h and 69i (cf. Table 10). By introducing the formyl group into the 10-position of benzoyl-substituted 9-styrylanthracene 69h, trans-9-styrylanthracene 7ld becomes photochemically inert, even in acetonitrile solution. Conceivably, the anthraldehyde chromophore in 71c and 71d acts as an energy sink. 

Resistance to degradation or cross-linking by radiation is also important.2,206 This is one advantage that poly(methylphenylsiloxane) has over poly(dimethylsiloxane) the phenyl groups are efficient energy sinks that tend to suppress the usual effects of radiation on a polymer. 

Solvents may enhance and impede molecular motions. There will be energy exchanges between reactants and solvents that may act as an energy sink or source. 

A noble metal is one that appears toward the bottom of a listing of standard reduction potentials as in Table 1 (page 11). From Fig. 7, you can see that such metals serve as lower-free energy sinks which can accept electrons from higher (less noble) metals. 

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