Isotope Effects in the Photoionization Yields and the Absorption Cross Sections for Ethylene and n-Butane

The absorption cross section σ and the photoionization yield η (the probability that photon absorption produces ionization), are reported for C2H4 and C2D4 at 44 photon energies between 10.44 and 11.78 eV, and they are reported for n-butane and n-butane-d10 at 37 photon energies between 10.56 and 11.78 eV. For ethylene, the nature of the isotope effects on η, σ, and the photoionization cross sections, σı(σı = ησ), indicates that the increase in η upon deuteration is not the result of a simple competition between pre-ionization processes and atomic-rearrangement processes in the superexcited states. The isotope effects for n-butane and the implications of the results for radiation chemistry are also discussed.