RATE COEFFICIENTS FOR SEVERAL TERNARY ASSOCIATION REACTIONS OF CH3+ IN THE TEMPERATURE-RANGE 100-300-K

The temperature variation of the ternary rate coefficients for the association of CH3+ with H2, CO, N2, O2 and CO2 with helium as the stabilizing third body have been studied in the range 100 K to 300 K using a selected ion flow tube apparatus. The ternary rate coefficients are found to have an inverse-power-law temperature dependence of the form k3 = AT-11 with n ≈ 3-4 over the temperature range studied. The pressure saturation of the effective binary rate coefficient for the CO reaction has been studied in some detail, and the onset of pressure saturation has also been observed at the lowest temperatures for the H2 and N2 reactions. The results are discussed in terms of a widely accepted mechanism for this type of reaction based on collisional energy transfer and the theory of unimolecular decomposition. The lifetimes of the CH3+ · X complexes against unimolecular decomposition at 100 K have been determined to be of the order of 10-7-10-8s. © 1979.