Ab initio chemical kinetics for the reactions of HNCN with O(~3P) and O_2

摘要

The kinetics and mechanisms of the reactions of cyanomidyl radical (HNCN) with oxygen atoms and molecules have been investigated by ab initio calculations with rate constant prediction. The doublet and quartet state potential energy surfaces (PESs) of the two reactions have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/ 6-311++G(d, p) level. The rate constants for various product channels of the two reactions in the temperature range of 300-3000 K are predicted by variational transition state and RRKM theories. The predicted total rate constants of the O( P) + HNCN reaction at 760 Torr Ar pressure can be represented by the expressions k_(total) (O + HNCN) = 3.12 × 10~(-10) × T~(-0.05) exp (-37/T) cm~3 molecule~(-1) s~(-1) at T=300-3000 K. The branching ratios of primary channels of the O(~3P) + HNCN are predicted: k_1 for producing the NO + CNH accounts for 0.72-0.64, k_2 + k_9 for producing the ~3NH + NCO accounts for 0.27-0.32, and k_6 for producing the CN + HNO accounts for 0.01-0.07 in the temperature range studied. Meanwhile, the predicted total rate constants of the O_2 + HNCN reaction at 760 Torr Ar pressure can be represented by the expression, k_(total)(O_2 + HNCN) = 2.10 × 10~(-16) × T~(1.28)exp (-12200/7) cm~3 molecule~(-1) s~(-1) at T= 300-3000 K. The predicted branching ratio for k_(11) + k_(13) producing HO_2 + ~3NCN as the primary products accounts for 0.98-1.00 in the temperature range studied.