Energy, during irradiation

The absorbed light may act as calalv. i for a spontaneous reaction, but in other cases it may supply energy to make possible a reaction which, without light, would be thermodynamically impossible. In some cases, such a reaction reverses itselfby thermal reaction (e.g. if left in the dark) and, hence, during irradiation a phoiostationary state is reached. 

Rearrangement of the 3,5-dimethylated carbene Id would yield the destabilized cyclopropene 3d with a methyl group in the bridgehead position 1, and consequently no detectable amount of cyclopropene 3d is formed during irradiation of Id. Indeed, whereas the 3,5-dimethyl substituted carbene Id is 3.4 kcal mol-1 more stable than the 2,6-dimethyl isomer lb, the stability is reversed for the cyclopropenes, as 3d is found to be 6.5 kcal mol-1 higher in energy than 3b at the B3LYP/6-31G(d) level of theory (Table 3). 

Figure 18 Schematic representation of the energy transfer to a trap site ( 0 ), formed during irradiation, depending on the molar fraction of CUA in LB films.

Irradiation of food inside the microwave oven causes photon uptake. The energy liberated each time a photon is absorbed is not sufficient to cause bond breakage (as was the case with UV light) nor can these microwave photons cause excitation of electrons (which is why we see a colour during irradiation with visible light but not with microwaves). Again, the energy is insufficient to... 

TEMPERATURE RISE DURING IRRADIATION. The chemical reactions which result from irradiation of polymers consume only a small fraction of the absorbed energy, which is mainly dissipated in the form of heat. Thus, 0.1 MGy of energy absorbed in water will produce a temperature rise of 24 °C - and more in a polymer. 

As shown in Table II, in the presence of polymer, the enclosed nitrous oxide is completely consumed during irradiation. In the place of nitrous oxide, nitrogen and water are formed. The yield of nitrogen or water corresponds stoichiometrically to the loss of nitrous oxide. A large G value, about 2000, is given for the disappearance of nitrous oxide. Estimation of the G value is based on the assumption that the available energy for the consumption is only that absorbed directly by the gas dissolved in the polymer solid. The G values for the formation of water and nitrogen should be equal to 2000. Moreover, the summation of the amount of the excess formation of crosslinks and unsaturation becomes stoichiometrically almost equal to the loss of nitrous oxide, as shown in Table III. The equation of material balance of nitrous oxide, therefore, should be written as follows ... 

The data points in the upper part of Figure 9 represent the creep rate during irradiation. Although there is some scatter in these data, a definite trend is evident, and the activation energy appears to be of... 

The increase in polystyrene creep rate owing to the radiation is directly proportional to the applied stress for a constant radiation intensity. The activation energy at constant radiation intensity for creep of polystyrene during irradiation at different temperatures is similar to the activation energy for creep without radiation. 

---