Deactivation by Collision in the Photolysis of Azoethane

Abstract

Though the excitation of azoethane by ultraviolet light is primarily an electronic process, a considerable fraction of the energy must go into the excitation of vibrations. As in unimolecular reactions, it is then possible for the vibrational energy to accumulate by chance in a weak bond, causing disruption of the molecule. On the other hand, deactivation may occur through collisions with other molecules. The greater the amount of energy put into the molecules, the more rapidly decomposition should occur and the less effective should be deactivation by collision. We have, therefore, investigated the photolysis at 3519, 3660, and 3776 Å, and, assuming deactivation at every collision, the average lifetimes of the activated molecules were determined to be roughly 1.6, 2.6, and 3.9×10⁻¹⁰ sec, respectively. The results have been compared with earlier results at 3660 Å at a series of different temperatures ranging up to about 120° above room temperature. They have been discussed in terms of the classical theory of unimolecular reactions. Though not all the parameters can be completely determined, and though some complications may be present, a reasonably good picture of the mechanism can be given on the basis of this theory.