Recoil relaxation process

It was proposed that the temperature dependence of polymer 5 arises from the temperature dependence of the kA step. Specifically, it was suggested that the polymer segments to which the radicals are attached are conformationally stressed. There are two possible modes for the newly formed radicals to relax and become separated They can rotate or recoil away from each other (Scheme 9). These secondary motions of the polymer arise from the relaxation of unfavorable bond conformations that are formed during the polymer casting process. The increased thermal energy facilitates the rotation and recoil relaxation processes, which effectively increases the rate constant for diffusion of the radicals out of the cage, kA. This leads to decreased radical-radical recombination and consequently an increase in photodegradation efficiency. 

SCHEME 9. Pathway for the increased separation efficiency of the radicals formed by irradiation of polymer 5. A rotation process is shown, but radical recoil will also lead to increased radical-radical separation. Relaxation of the polymer chains leads to an increase in kd and a subsequent increase in the quantum yield for degradation. 

Inspiration is an active process involving the diaphragm and external intercostal muscles. Expiration is normally passive, because of relaxation of these muscles and recoil of lung tissue. 

A more carefully constructed approach to energy transfer explicitly accounts for the energy distribution of the chemically activated product (5,6,26,27), The initial distribution of energies upon production as well as the transient distributions formed by collisional relaxation of internal energy are used to calculate rate constants for imimolecular reaction. The formalism of Bunker (7,8,9) based on general RRKM theory is convenient for recoil chemical activation, since it explicitly accounts for both rotational and vibrational excitation in the product. In the cyclobutane model system reported, a stepladder approach to deactivation was incorporated, with the step size being a parameter determined by the best fit to the data (6). The overall processes considered are illustrated in Equation 4. 

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