The solid phase photolysis and radiolysis of ethylene at 20 to 77 K

Films of ethylene condensed onto a cold finger maintained at 20 K were irradiated with photons whose energy ranged from 8.4 to 21.2 eV. At the higher photon energies the relative yields of products compare well with those seen in the radiolysis of solid ethylene. Experiments on CH₂CD₂ demonstrate that in the photolysis hydrogen is mainly formed by the elimination processes CH 2 CD 2 * → H 2 ( D 2 ) + C 2 D 2 ( C 2 H 2 ) and CH 2 CD 3 * → HD + C 2 HD . The relative probabilities of these three processes are independent of the energy of the incident photons from 8.4 to 11.6 eV and are within experimental error identical to those observed in earlier gas phase photolysis experiments. Relative to acetylene, cyclobutane is a minor product at 8.4 eV but increases by an order of magnitude at higher energies where ions play a role. Cyclobutane, 1-butene and methylcyclopropane formed upon irradiation of frozen C₂H₄ - C₂D₄ mixtures consisted mainly of C₄D₈, C₄D₄H.₄, and C₄H₈. Plausible mechanisms which may account for the formation of the latter products are examined. In the solid phase as in the gas phase the relative importance of H-atom production is seen to increase with increasing photon energy. Cyclopropane, apparently formed by insertion of CH₂ into C₂H₄, is observed as a product at all wavelengths in the photolysis, and in the radiolysis.