Translational Energy Release in the Photodissociation of Aromatic Molecules

Abstract

When a large amount of energy is suddenly placed in an aromatic molecule, it can dissociate via a rather complex path. Measurements of translational energy distributions of the dissociated fragments of a variety of related molecules at different wave lengths clarify the dissociation processes. The reactions considered are

aryl halides + h√→ aryl radical + halogen atom

s-triazine + h√→ 3 HCN

styrene or cyclooctatetraene + h√→ benzene + acetylene The first reaction may involve direct cleavage of the C-X bond but when it does not there is an electronic energy transfer from the delocalized Π system to the C-X bond. The second and third reactions involve dissociations from vibrationally hot electronic ground states and comparatively little kinetic energy is released. The use of isotopically labelled styrene shows that rather extensive hydrogen atom migration precedes dissociation.