Irradiation of Xenon–Propane and Argon–Propane Mixtures with γ Rays and 21.2-eV Photons

Mixtures of xenon or argon with propane (20:1) were irradiated in the presence of radical scavengers by $\gamma$ rays and by 21.2‐eV photons from a helium resonance lamp. The ion‐pair yields of products orginating from ionic fragmentation reactions or ion–molecule reactions are derived from isotopic analysis of product molecules formed in C₃D₈–C₃H₈ mixtures or in CD₃CH₂CD₃. At a given pressure, there are only small differences between the radiolysis and photolysis in the modes of dissociation of parent propane ions formed by charge transfer with a particular rare gas. Higher‐energy ionic fragmentation processes are quenched when the pressure is increased; in the case of xenon–propane mixtures it is demonstrated that the parent ion yield increases as primary fragmentation processes are quenched. In the irradiated argon–propane–scavenger mixtures, isotope effects on the ionic fragmentation of the excited deuterated fragment ions are pronounced. The decomposition of neutral propane molecules excited to lower resonance states accounts for not more than 10%–12% of the product‐forming processes in the xenon mixtures.