Computational exploration of regioselectivity and atmospheric lifetime in NO3-initiated reactions of CH3OCH3 and CH3OCH2CH3

Abstract

The NO₃-initiated reactions of CH₃OCH₃ and CH₃OCH₂CH₃ have been investigated by the BHandHLYP method in conjunction with the 6-311G(d,p) basis set. Thermodynamic and kinetic data are further refined using the comparatively accurate CCSD(T) method. According to the values of reaction enthalpies (ΔH_r,298^θ) and reaction Gibbs free energies (ΔG_r,298^θ) from CH₃OCH₂CH₃ with NO₃ system, we find that H-abstraction pathway from the α-CH₂ group is more exothermic. It is further confirmed by the calculated CH bond dissociation energy of CH₃OCH₂CH₃ molecule. All the rate constants, computed through means of canonical variational transition state with small-curvature tunneling correction, are fitted to the three-parameter expressions k₁=1.54×10^-23T^3.34exp(-1035.53/T) and k₂=3.55×10^-26T^4.31exp(-281.24/T)cm³molecule^-1s^-1 and branching ratios are computed over the temperature range 200-600K. The branching ratios are also discussed. The atmospheric lifetimes of CH₃OCH₃ and CH₃OCH₂CH₃ determined by the NO₃ radical are about 270 and 29days, respectively.

Keywords: Atmospheric lifetime; Branching ratio; Transition state.