Can a single water molecule really affect the HO₂+ NO₂hydrogen abstraction reaction under tropospheric conditions?

Abstract

The effect of a single water molecule on the HO2 + NO2 hydrogen abstraction reaction has been investigated by employing B3LYP and CCSD(T) theoretical approaches with the aug-cc-pVTZ basis set. The reaction without water has three types of reaction channels on both singlet and triplet potential energy surfaces, depending on how the HO2 radical approaches NO2. These correspond to the formation of trans-HONO + O2, cis-HONO + O2 and HNO2 + O2. Our calculated results show that triplet reaction channels are favorable and their total rate constant, at 298 K, is 2.01 × 10(-15) cm(3) molecule(-1) s(-1), which is in good agreement with experimental values. A single water molecule affects each one of these triplet reaction channels in the three different reactions of H2O···HO2 + NO2, HO2···H2O + NO2 and NO2···H2O + HO2, depending on the way the water interacts. Interestingly, the water molecule in these reactions not only acts as a catalyst giving the same products as the naked reaction, but also as a reactant giving the product of HONO2 + H2O2. The total rate constant of the H2O···HO2 + NO2 reaction is estimated to be slower than the naked reaction by 6 orders of magnitude at 298 K. However, the total rate constants of the HO2···H2O + NO2 and NO2···H2O + HO2 reactions are faster than the naked reaction by 4 and 3 orders of magnitude at 298 K, respectively. Their total effective rate constant is predicted to be 1.2 times that of the corresponding total rate constant without water at 298 K, which is in agreement with the prediction reported by Li et al. (science, 2014, 344, 292-296).

Effects of water, ammonia and formic acid on HO2 + Cl reactions under atmospheric conditions: competition between a stepwise route and one elementary step

“…and S3, † and consistent with previous reports,[62][63][64][65][66] a ve-membered ring complex H 2 O/HO 2 is much more stable than the single hydrogen bond(or van der Waals interaction) complexes HO 2 /H 2 O, H 2 O/Cl and Cl/ H 2 O with its binding energy being larger by 5.1-6.1 kcal mol À1 . Meanwhile, the equilibrium constants of these complexes at 298 K are 6.05 Â 10 À20 , 2.60 Â 10 À22 , 1.93 Â 10 À21 and 3.85 Â 10 À21 cm 3 per molecule, respectively (Table S3 †).…”

Catalytic effect of (H2O)n (n = 1–3) on the HO2 + NH2 → NH3 + 3O2 reaction under tropospheric conditions

“…As seen in Fig. 2 and Table S2, † consistent with previous reports, 24,25,28,37,66 Regarding to Channel WM1, by different collisions between H 2 O/HO 2 and NH 2 , two kinds of reaction types have been found, which were labeled as Channel WM1a and Channel WM1b. For Channel WM1a, starting from H 2 O/HO 2 + NH 2 reactants, hydrogen-bonded complex IM_WM1 was formed by the interaction between N atom of NH 2 radical and one H atom of the H 2 O moiety in H 2 O/HO 2 complex with a bonding energy of 5.5 kcal mol À1 .…”

“…However, the triplet potential energy surface of reaction (3), especially, the triplet hydrogen abstraction (HA) is not involved, which is not neglected for the HA in many previous reports reaction between radical and HO 2 radical. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Even in some HA reaction, triplet HA is favorable kinetically. 16,18,20,23,26,29,30 So, both the singlet and triplet HA have been investigated at the CCSD(T)//B3LYP/6-311++G(3df,3pd) level by Xiang et al 31 In their work, for the favorable HA, the reaction mechanism on the triplet potential surface to be mainly a barrierless addition of HO 2 to NH 2 leading to an intermediate OOH/NH 2 ( 3 im1), and then the adduct 3 im1 goes through an H transfer forming the product of NH 3 and 3 O 2 .…”

Influence of H2O and NH3 on the reaction of HO2 with NO in troposphere: Theoretical investigation of HNO3 formation pathways

“…HNO 3 reaction. Indeed, in previous water-medium A + B reactions, [30][31][32][33][34][35][36][37][38][39][40][41][42] both the bimolecular reactions of AÁÁÁH 2 O + B and BÁÁÁH 2 O + A have not been neglected. So, it is unclear whether the water-assisted reaction mechanism of the HO 2 + NO !…”