Role of the (H₂O)_n (n = 1–3) cluster in the HO₂ + HO → ³O₂ + H₂O reaction: mechanistic and kinetic studies

Abstract

To study the catalytic effects of (HO) (n = 1-3), the mechanisms of the reaction HO + HO →O + HO without and with (HO) (n = 1-3) have been investigated theoretically at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ level of theory, coupled with rate constant calculations using the conventional transition state theory. Our results show that upon incorporation of (HO) (n = 1-3) into the channel of HO + O formation, two different reactions, i.e. HO + HO(HO) (n = 1-3) and HO + HO(HO) (n = 1-3), have been observed, and these two reactions are competitive with each other. The catalytic effects of (HO) (n = 1-3) mainly arise from the contribution of a single water vapor molecule; this is because the effective rate constants with water are respectively larger by 2-3 and 3-4 orders of magnitude than those of the reactions with (HO) and (HO). Furthermore, the catalytic effects of the water monomer mainly arise from the HOHO + HO reaction, and the enhancement factor of this reaction is obvious within the temperature range of 240.0-425.0 K, with the branching ratio (k'(RW)/k) of 17.27-80.77%. Overall, the present results provide a new example of how water and water clusters catalyze gas phase reactions under atmospheric conditions.

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

“…† Specically, the calculated results using M06-2X/aug-cc-pVTZ indicate that the rate constant is increased by 32% and 20% due to tunneling, while the rate constant is decreased to 44% and 60% at 275 and 320 K, respectively. So, similar with previous investigations, 64,65 As seen in Fig. 2 and S1, † as the number of water molecules increases in a given cluster of HO 2 / (H 2 O) n (n ¼ 1-3) and H 2 N/(H 2 O) n (n ¼ 1-3), the number of possible congurations for the cluster increases quickly, and each of the congurations becomes increasingly complicated.…”

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

“…When H 2 O/HO 2 and Cl act as reactants, Channel RWM1 occurs in two steps, as depicted in Fig. 3, which is similar to the H 2 O-catalyzed reactions 66,74 of HO 2 + HO and HO 2 + HS. The rst step begins with the formation of the pre-reactive IM_WM1 complex, which transforms into the IM_WM2 product through the TS_WM1 transition state via a ring enlargement, while the second step is IM_WM2 isomerization into H 2 O/Cl-H + 3 O 2 via TS_WM2, which was discussed above.…”

Effect of NH3 and HCOOH on the H2O2 + HO → HO2 + H2O reaction in the troposphere: competition between the one-step and stepwise mechanisms

“…2(b). When binary complex H 2 O 2 /NH 3 and HO play as reactants, the reaction occurs in stepwise route, which is similar to H 2 O catalyzed reactions 21,28,62,73,74 of HO 2 + HO, HO 2 + HS, H 2 O 2 + HO, HO 2 + Cl, and HO 2 + NH 2 , as well as NH 3 -catalyzed HO 2 + Cl reaction. 28 The rst step begins with pre-reactive complex IM_AM2, which transforms into seven-membered ring complex IM_AM3 through transition state TS_AM2 by a ring enlargement.…”

“…It should be noted that K eq2 calculated here has been successfully performed in calculating the complexes[61][62][63][64][65] of H 2 O/VOC, H 2 O/HCHO, H 2 O/CH 3 COCH 3 , H 2 O/CH 2 NH, H 2 O/HO 2 , H 2 O/SO 2 , and H 2 O/NO 2 .…”