Ab initio Studies of ClO_x Reactions: Prediction of the Rate Constants of ClO+NO₂ for the Forward and Reverse Processes

Abstract

The potential-energy surface for the reaction of ClO with NO2 has been constructed at the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) level of theory. Six ClNO3 isomers are located; these are ClONO2, pc-ClOONO, pt-ClOONO, OClNO2, 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 ClONO2, the predicted low- and high-pressure-limit rate constants in N2 for the temperature range of 200-600 K can be represented by: (N2)=3.19 x 10-17 T-5.54 exp(-384 K/T) cm6 molecule-2 s-1 and =3.33 x 10-7 T-1.48 exp(-18 K/T) cm3 molecule-1 s-1. The predicted low- and high-pressure-limit rate constants for the decomposition of ClONO2 in N2 at 200-600 K can be expressed, respectively, by =6.08 x 1013 T-6.54 exp(-13813 K/T) cm3 molecule-1 s-1 and =4.59 x 1023 T-2.43 exp(-13437 K/T) s-1. The predicted values compare satisfactorily with available experimental data. The reverse Cl+NO3 reaction was found to be independent of the pressure, giving exclusively ClO+NO2; the predicted rate constant can be expressed as k(Cl+NO3)=1.19 x 10-9 T-0.60 exp(58 K/T) cm3 molecule-1 s-1..

Ab initio chemical kinetics for the ClOO + NO reaction: Effects of temperature and pressure on product branching formation

“…Barrier energy for same reaction was reported to be 6.7 kcal/mol by Zhu et al at the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) level. 19 The exothermicity for formation of ClONO 2 (38.3 kcal/mol) from ClOO + NO reaction is in good agreement with the experimental heat of reaction, −37.4 ± 0.7 kcal/mol. 32,34 In this potential energy surface, the cleavage of the O-N and O-Cl bond in the ClONO 2 isomer giving the products ClO + NO 2 and Cl + NO 3 is predicted to be endothermic by 25.0 and 39.1 kcal/mol, respectively.…”

“…19 In this work, we focused on the effects of temperature and pressure on chlorine nitrate formation and decomposition. The heats of formation of many of unstable intermediates such as ClOONO isomers have been predicted in this study.…”

Theoretical study of the mechanism for the ClOO + NO reaction on the singlet potential energy surface

“…The optimized geometries and harmonic frequencies of the reactant, products, local minima, and transition states are obtained at the UB3LYP/ 6-311?G(2d) theory level. The density functional theoretical methods are employed here because they have shown good and high efficient performance in the studies of reaction mechanism for some halogen containing species [21][22][23][24]. Vibrational frequencies are calculated at the UB3LYP/6-311?G(2d) level to check whether the obtained stationary point is an isomer or a first-order transition state.…”

Theoretical study on the reaction of CN radicals with ClO radicals by density functional theory

“…Path 1 (P 4 ): R−1−TS1/P 4 −P 4 Path 1 (P 1 ) R−1−TS1/P 4 −P 4 −TSP4/2−2−TS2/P 1 −P 1 Path 1 (P 3 ) R−1−TS1/P 4 −P 4 −TSP 4 /2−2−TS2/4−4− TS4/P 3 −P 3 Path 6 (P 3 ) R−5−TS4/5−4−TS4/P 3 −P 3 The rate-determining transition state involved in Path 1 (P 1 ), Path 1 (P 3 ) and Path 6 (P 3 ) lies significantly higher than TS1/P 4 involved in Path 1 (P 4 ). Therefore, compared with Path 1 (P 4 ), the latter three paths may have negligible contribution to the title reaction.…”

“…Because of its participation in the catalytic cycle of the stratospheric ozone depletion, ClO has been studied by theoretical and experimental research [1,2] . A large number of experimental and theoretical investigations have been reported on the reactions between ClO radicals and other species such as NO 2 , CH 3 S, and NH 2 [3][4][5] . The CN radical is considered when diverse chemical environments are studied, including combustion chemistry, interstellar clouds, and our own atmosphere.…”