An experimental and theoretical study of the gas phase kinetics of atomic chlorine reactions with CH3NH2, (CH3)2NH, and (CH3)3N

Abstract

The rate coefficients for the reactions of Cl(²P_J) with methylamine (R1), dimethylamine (R2) and trimethylamine (R3) have been measured using the laser flash photolysis – resonance fluorescence technique as a function of temperature (274–435 K) and pressure (25–400 Torr N₂). The experimental data are well-represented by the following temperature- and pressure-independent rate coefficients (10¹⁰ × k/cm³ molecule⁻¹ s⁻¹): k_R1 = 2.90 ± 0.44, k_R2 = 3.89 ± 0.58, k_R3 = 3.68 ± 0.55; the uncertainties are estimates of accuracy at the 95% confidence level. Potential energy surfaces (PES) for the reactions have been characterized at the MP2/cc-pVTZ level and improved single point energies of stationary points obtained in CCSD(T)-F12a calculations. The PES for all reactions are characterized by the formation of pre and post reaction complexes and submerged barriers. Rate coefficients for the reactions were calculated as a function of temperature and pressure using a master equation model based on the coupled cluster theory results. The calculated rate coefficients are in good agreement with experiment; the overall rate coefficients are relatively insensitive to variations of the barrier heights within typical chemical accuracy, but the predicted branching ratios vary significantly. The inclusion of tunnelling has no effect.