Matrix-Induced Intersystem Crossing in the Photochemistry of the 1,2-Dichloroethenes

Article abstract of DOI:10.1021/j100343a026

The photoproducts of the 1,2-dichloroethenes (DCE) in xenon matrix at 12 K differ from those observed in krypton matrix.In xenon, photolysis at 237 nm of both cis- and trans-dichloroethene results in elimination of both Cl2 and HCl as well as isomerization, whereas only HCl elimination and isomerization are observed in krypton.Longer wavelength irradiation has no effect on either DCE in Kr but produces small, distinct amounts of products in Xe.The results indicate that in xenon, chemistry is occuring through a triplet state as well as from the directly excited singlet state.Enchanced spin-orbit coupling in the heavy-atom environment facilitates intersystem crossing from the initial singlet to a triplet surface, as well as, no doubt enhanced absorption directly into the triplet state.These effects provide access to the normally spin-forbidden chlorine elimination channel.The appearance of products in Xe at the lower photon energies is ascribed to direct T₁ <- S₀ absorption, assisted by the external heavy atom.