Motion light energy production

In addition to an oxidizer, pyrotechnic mixtures will also contain a good fuel - or electron donor - that reacts with the liberated oxygen to produce an oxidized product plus heat. This heat will enable the high-energy chemist to produce any of a variety of possible effects - color, motion, light, smoke, or noise. 

In this reaction, light of appropriate energy is used to selectively excite 1,3-cyclohepta-diene. The diene closes to a cyclobutene by a disrotatory motion. Although the product, because of its strained cyclobutene ring, is much less stable than the reactant, it is unable to revert back to the diene by an allowed pathway. It does not absorb the light used in the reaction, so the photochemically allowed disrotatory pathway is not available. A conrotatory opening is thermally allowed but results in a cycloheptadiene with a trans double bond. Such a compound is much too strained to form. Therefore, the product can... 

Light intensity at the usual levels seldom has an effect on the primary photochemical step if all other variables are kept constant, although it may affect overall results considerably since it may control the concentrations of reactive intermediates. However, it will affect the outcome of a competition between primary one-photon and two-photon processes. The latter are still somewhat of a rarity but may be more important than is commonly realized, namely in rigid media where triplets have long lifetimes and quite a few of them are likely to absorb a second photon. The additional available energy may permit motion to new minima in Ti and thus give new products. 

Although the nuclear partition function is a product of the translational, rotational, and vibrational partition functions, the isotope effect is determined almost entirely by the latter, specifically by vibrational modes involving motion of isotopically different atoms. In the case of light atoms (i.e., protium vs. deuterium or tritium) at moderate temperatures, the isotope effect is dominated by ZERO-POINT energy differences. 

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