Ab initio Studies of ClO x Reactions: Prediction of the Rate Constants of ClO+NO 2 for the Forward and Reverse Processes

The potential‐energy surface for the reaction of ClO with NO 2 has been constructed at the CCSD(T)/6‐311+G(3df)//B3LYP/6‐311+G(3df) level of theory. Six ClNO 3 isomers are located; these are ClONO 2 , pc‐ClOONO, pt‐ClOONO, OClNO 2 , pt‐OClONO, pc‐OClONO, with predicted energies relative to the reactants of −25.6, −0.5, 1.0, 1.9, 12.2 and 13.6 kcal mol −1 , and heats of formation at 0 K of 7.8, 32.9, 34.4, 35.5, 45.6 and 47.0 kcal mol −1 , respectively. Isomerizations among them are also discussed. The rate constants for the low‐energy pathways have been computed by statistical theory calculations. For the association reaction producing exclusively ClONO 2 , the predicted low‐ and high‐pressure‐limit rate constants in N 2 for the temperature range of 200–600 K can be represented by: ${{\rm{k}}_1^0 }$ (N 2 )=3.19×10 −17 T −5.54   exp(−384 K/ T ) cm 6   molecule −2   s −1 and ${{\rm{k}}_1^\infty }$ =3.33×10 −7 T −1.48   exp(−18 K/ T ) cm 3   molecule −1   s −1 . The predicted low‐ and high‐pressure‐limit rate constants for the decomposition of ClONO 2 in N 2 at 200–600 K can be expressed, respectively, by ${{\rm{k}}_{ - 1}^0 }$ =6.08×10 13 T −6.54   exp(−13813 K/ T ) cm 3   molecule −1   s −1 and ${{\rm{k}}_{ - 1}^\infty }$ =4.59×10 23 T −2.43   exp(−13437 K/ T ) s −1 . The predicted values compare satisfactorily with available experimental data. The reverse Cl+NO 3 reaction was found to be independent of the pressure, giving exclusively ClO+NO 2 ; the predicted rate constant can be expressed as k (Cl+NO 3 )=1.19×10 −9 T −0.60   exp(58 K/ T ) cm 3   molecule −1   s −1 .