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.