Electron Trapping and Hydrogen-Atom Reactions in Irradiated Polyethylene

The absorption spectrum of electrons trapped in polyethylene during irradiation at low temperature is studied here, and an approximate G value for this of ∼0.8 at low doses is deduced. The spectrum stretches from the vacuum ultraviolet to the infrared (thus differing entirely from that in short-chain branched alkanes) and changes somewhat with increasing irradiation dose. Another absorption spectrum is found, which bleaches thermally but not optically, that is probably due to alkyl radicals. Thermal H atoms were studied at low temperature by adding benzene to the polyethylene and observing the ultraviolet absorption spectrum of the resulting cyclohexadienyl radicals. The G value for thermal H-atom production was found to be ∼1.8, similar to the value in short-chain alkanes at room temperature, and the atoms apparently migrated considerable distances even at −170°C. Addition also of olefin with the benzene showed that olefin double bonds react ∼600 times more efficiently with thermal H atoms than do methylene groups, but despite this H-atom capture is not an important mechanism for the destruction of these double bonds by radiation.