Photoionization of Propylene at 1236 Å. Reactions of C3D6+ with Added Alkanes

Abstract

C₃H₆–C₃D₆–O₂ mixtures have been irradiated at 1236 Å (10 eV) in the presence and absence of an applied electrical field with the purpose of obtaining information about the ion—molecule reaction mechanism. On the basis of a number of observations, it was concluded that the product, propane, can be ascribed to the reaction C_3mH_6m⁺+C₃H₆→C_3mH_6m−2⁺+C₃H₈ (m≥2). When alkanes (RH₂) whose ionization energy is larger than 10 eV are added to C₃D₆—O₂ mixtures, the following H₂⁻‐transfer reaction occurs: C₃D₆⁺+RH₂→CD₃CDHCD₂H+R⁺ . Relative rates of the reaction of C₃D₆⁺ with various alkanes have been determined and compare favorably with values obtained in a recent radiolytic study in which cyclopentane‐d₁₀ was used as a source of C₃D₆⁺ ions. The optimum experimental conditions, under which meaningful saturation ion currents can be obtained in the photoionization apparatus, are discribed. On the basis of measurements of the saturation ion current in NO and propylene at 1236 Å, values of 0.197 and 0.208 were obtained for the photoionization efficiencies of C₃H₆ and C₃D₆, respectively. The latter measurements made it possible to express the products in the number of molecules formed per ion pair as well as in the number of molecules formed per quantum absorbed.