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A detailed effects of catalyst X (X = H2O, (H2O)2, NH3, NH3···H2O, H2O···NH3, HCOOH and H2SO4) on the HO4H → O3 + H2O reaction have been investigated by using quantum chemical calculations and canonical vibrational transition state theory with small curvature tunnelling. The calculated results show that (H2O)2-catalysed reactions much faster than H2O-catalysed one because of the former bimolecular rate constant larger by 2.6–25.9 times than that of the latter one. In addition, the basic H2O···NH3 catalyst was found to be a better than the neutral catalyst of (H2O)2. However it is marginally less efficient than the acidic catalysts of HCOOH, and H2SO4. The effective rate constant (k't) in the presence of catalyst X have been assessed. It was found from k't that H2O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320 K at 0 km altitude. However, compared with the rate constant of HO4H → H2O + O3 reaction, the keff values for H2O catalysed reaction are smaller by 1–2 orders of magnitude, indicating that the catalytic effect of H2O makes a negligible contribution to the gas phase reaction of HO4H → O3 + H2O. Highlights A detailed effects of catalyst of H2O, (H2O)2, NH3, NH3···H2O, H2O···NH3, HCOOH and H2SO4 on the HO4H → O3 + H2O reaction has been performed. From energetic viewpoint, H2SO4 exerts the strongest catalytic role in HO4H → O3 + H2O reaction as compared with the other catalysts. At 0 km altitude H2O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320 K. HO4H → H2O + O3 reaction with H2O cannot be compete with the reaction without catalyst, due to the fact that the effective rate constants in the presence of H2O are smaller. [ABSTRACT FROM AUTHOR]

Effects of (H2O)n (n = 1-3) on the H2O2 + HO → HO2 + H2O reaction have been investigated by the reactions of H2O2L(H2O)n (n = 1-3) + HO and H2O2 + HOL(H2O)n (n = 1-3) at the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level of theory, coupled with rate constant calculations by using canonical variational transition state theory. Interestingly, for the former reactions, one-step process and stepwise mechanism are involved, where one-step processes occurring though cage-like hydrogen bonding network complexes and the transition states are favourable. Due to larger effective rate constants, these favourable processes are also favourable than the corresponding latter reactions. Meanwhile, the catalytic effect of (H2O)n (n = 1-3) is mainly taken from water monomer, because the effective rate constant (k'(R_WM2)) of H2O2···H2O + HO reaction is, respectively, larger by 3, 6-10 orders of magnitude than that of H2O2···(H2O)2 + HO (k'(R_WD1)) and H2O2···(H2O)3 + HO (k'(R_WT1)) reactions. Furthermore, the enhancement factor of water molecular (k'(R_WM2)/ktot) is only 0.28% at 240 K, while at high temperature (such as at 425 K), the positive water vapour effect enhances up to 27.13%. This shows that at high temperatures the positive water effect is obvious under atmospheric conditions. [ABSTRACT FROM AUTHOR]

The isomerization of CH3S(OH)CH2 to CH3S(O)CH3 in the absence and presence of water has been investigated at the G3XMP2//B3LYP/6-311+G(2df,p) level. The naked isomerization, the reaction without water, gives the high barrier height (21.56 kcal·mol−1). Three models are constructed to describe the water influence on the isomerization, that is, water molecules are the catalyst and the microsolvation, and water molecules act as the catalyst and microsolvation simultaneously. Our results show that the isomerization barrier heights of CH3S(OH)CH2 to CH3S(O)CH3 are reduced by 12.32, 11.04, and 7.80 kcal·mol−1, respectively, when one, two, and three water molecules are performed as catalyst, in contrast to the naked isomerization. Moreover, the rate constants of the isomerization are calculated using the transition state theory with the Wigner tunneling correction over the temperature range of 240-425 K. We find that the rate constant of a single water molecule as the catalyst is 1.58 times larger than the naked isomerization at 325 K, whereas it is slower by 6 orders of magnitude when water molecule serves as the microsolvation at 325 K, compared to naked reaction. So the water-catalyzed isomerization of CH3S(OH)CH2 to CH3S(O)CH3 is predicted to be the key role in lowering the activation energy. The isomerization involving water molecules acting as microsolvation is unfavorable under atmospheric conditions. [ABSTRACT FROM AUTHOR]

The singlet and triplet reaction mechanisms and rate constants for CH3CH2O + HO2 and CH3CHOH + HO2 reactions were investigated by employing the high‐level quantum chemical calculations with CBS‐QB3 theoretical method and conventional transition state theory with the Wigner tunneling correction. For CH3CH2O + HO2 reaction, four direct hydrogen abstraction processes and five addition‐elimination channels were identified, while two direct hydrogen abstraction routes and nine addition‐elimination channels were found in CH3CHOH + HO2 reaction. The results show that the triplet addition‐elimination channels of CH3CH2OH + 3O2 and CH3COOH + H2O are, respectively, the most favorable channels for CH3CH2O + HO2 and CH3CHOH + HO2 reactions. This is because that they have lower energy barrier and their contribution to the overall rate constants are, respectively, 57% to 86% and 44% to 80%. This work may lead to a better understanding of the mechanism and the kinetic for the singlet and triplet reactions of CH3CH2O + HO2 and CH3CHOH + HO2. Direct hydrogen abstraction routes and addition‐elimination channels were found in CH3CH2O + HO2 and CH3CHOH + HO2 reactions. Triplet addition‐elimination channels of CH3CH2OH + 3O2 and CH3COOH + H2O are, respectively, the most favorable channels for CH3CH2O + HO2 and CH3CHOH + HO2 reactions. In the calculated temperature range, the rate constants of the major channels all decrease with temperature increase. [ABSTRACT FROM AUTHOR]