Total and Dissociative Charge Transfer of Positive Ions with Perfluoroalkanes Studied by Mass Spectrometry

Abstract

Total and dissociative charge‐transfer cross sections of rare gas and molecular positive ions with CF₄, C₂F₆, C₃F₈, n‐C₄F₁₀, and cyclo‐C₄F₈ are reported. The positive ions had an average energy of 50 eV so an electron jump mechanism occurs. When the total cross sections are plotted against the projectile ion recombination energy pseudoresonance effects are seen. It is suggested that the total cross section depends on the Franck—Condon factors for the transition of the neutral target molecule to a vibrationally excited ion. Thus higher vibrational states are less probable since they are generally associated with lower Franck—Condon factors. The highest cross sections occur with ${\mathrm{N}}_2^{+}$ . For a given projectile ion the total cross sections increase with the molecular weight of the fluorocarbons. The dissociative cross‐section data indicates fragment ion appearance potentials in remarkably good agreement with recent photoionization measurements except for ${\mathrm{CF}}_3^{+}$ from CF₄.