Association Reactions at Low Pressure. 2. The CH3+/CH3CN System

Article abstract of DOI:10.1021/j100347a039

The reaction between CH3⁺ and CH3CN has been examined at pressures between 8E-8 and 1E-3 Torr in an ion cyclotron resonance mass spectrometer.At low pressures the reaction is bimolecular, having a rate coefficient of 1.8E-9 cm³s^-1.The major ion products are H2CN⁺ and C2H5⁺, but a bimolecular association channel also competes with these two main binary exotermic channels.At pressures above ca. 4E-5 Torr the termolecular associaton (CH3CNCH3⁺) reaction becomes the major reaction.The results are rationalized in terms of barriers on the potential energy surface of the binary exit channels.The rate coefficient observed for the termolecular associaton reaction CH3⁺ + CH3CN + M <*> CH3CNCH3⁺ + M was found to be k=1.90E-22 cm⁶ s^-1 when M=CH3CN, and when M=N2, Ne, and He, k=4.0E-23, 0.6E-23, and 1.0E-23 cm⁶ s^-1 respectively.The lifetime of the collision complex was found to be >14 μs.