Ion–molecule reactions in the systems CF₄–CH₄ and CF₄–C₂H₆

A mass spectrometric study of ionic reactions in CH₄−CF₄ and C₂H₆−CF₄ mixtures was undertaken at pressures as high as 0.52 torr. It was found that CF₃⁺ ions react in a hydride transfer process with ethane with a rate constant of 3.3×10⁻¹⁰ cm³ molecule⁻¹⋅s⁻¹. A rate constant of 1.6×10⁻¹⁰ cm³ molecule⁻¹⋅s⁻¹ was determined for the reaction of C₂H₅⁺ ions with C₂H₆. In mixtures of CH₄ and CF₄, both CH₃⁺ and CH₅⁺ react with CF₄, apparently by fluoride ion transfer, for which we calculated rate constants of 8.6×10⁻¹⁰ and 2.3×10⁻¹⁰ cm³ molecule⁻¹⋅s⁻¹, respectively. CF₃⁺ ions do not attack molecular methane. There is good agreement with published rate constants for the disappearance of CH₂⁺, CH₃⁺, and CH₄⁺ ions in pure methane. However we observed a decreasing CH₅⁺ yield above 0.1 torr which may be due either to impurities or to excess energy in CH₅⁺ ions as a result of a relatively high repeller field strength within the ion source in our experiments.