Abstract
The rate coefficients for the reactions of Cl((2)PJ) 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 (10(10) × k/cm(3) molecule(-1) s(-1)): kR1 = 2.90 ± 0.44, kR2 = 3.89 ± 0.58, kR3 = 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.
Highlights
The rate coefficients for the reactions of Cl(2PJ) 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)
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
There are no kinetic data for Cl + amine reactions reported in the literature, one reaction dynamics study of Cl + CH3NH2 has been published showing yields of the two hydrogen abstraction products to be 48% CH2NH2 and 52% NHCH3 at a collision energy of B2000 cmÀ1.12 Since it is a reasonable expectation that Cl + amine reactions are very fast, laboratory studies to quantify the kinetics of these reactions are needed
Summary
The rate coefficients for the reactions of Cl(2PJ) 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). It has been reported that levels of Cl atoms in the marine boundary layer can be 1–10 percent of OH levels,[9] and findings suggest a significant Cl production rate even in the middle of the continental United States.[10] Laboratory and theoretical research demonstrates that heterogeneous reaction of N2O5 with HCl(aq) may represent a significant source of tropospheric ClNOx species that can rapidly photolyze under daytime conditions to generate Cl atoms.[11] it appears that reaction with Cl could be a significant tropospheric sink for any trace gas that reacts with Cl significantly more rapidly than with OH. Experimental determinations of temperature- and pressuredependent rate coefficients for (R1)–(R3) are reported for the first time, as are theoretical analyses of reaction potential energy surfaces and kinetics. The potential influence of (R1)–(R3) on the atmospheric chemistry of the studied amines is qualitatively assessed
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