Kinetic mass spectrometric investigation of the ion-molecule reactions occurring in C4 and C5 alkanes following photoionization at 106.7 and 104.8 nm

The photoionization of C₄ and C₅ alkanes has been investigated at 106.7 and 104.8 nm in a mass spectrometer specifically designed for the investigation of ion-molecule reactions occurring at thermal kinetic energies. Absolute rate constants are reported for the reactions of various fragment ions with the corresponding parent molecule. The rate constants found for reactions of sec - C 3 H 7 + ions with i-C₄H₁₀, n-C₄H₁₀, i-C₅H₁₂, and n-C₅H₁₂ were found to be 3.3, 4.4, 4.7, and 5.2 × 10^-10 cm³/molecule-second respectively. The C 4 H 9 + ions were also found to be highly reactive, exhibiting rate constants of 3.6 and 3.8 × 10^-10 cm³/molecule-second in reactions with i-C₅H₁₂ and n-C₅H₁₂. The rate constants for reaction of C 3 H 6 + with i-C₄H₁₀, n-C₄H₁₀, i-C₅H₁₂, and n-C₅H₁₂ were found to be 4.9, 4.9, 7.6, and 7.9 × 10^-10 cm³/molecule-second, respectively. Butene ions are less reactive by an order of magnitude. The results are compared with complementary data derived from electron impact experiments, and the relationship between the structure and reactivity of the various ions is discussed.