Ab Initio Study on the Mechanism of the Atmospheric Reaction OH+O₃→HO₂+O₂

Abstract

The atmospheric reaction (1) OH + O3-->HO2 + O2 was investigated theoretically by using MP2, QCISD, QCISD(T), and CCSD(T) methods with various basis sets. At the highest level of theory, namely, QCISD, the reaction is direct, with only one transition state between reactants and products. However, at the MP2 level, the reaction proceeds through a two-step mechanism and shows two transition states, TS1 and TS2, separated by an intermediate, Int. The different methodologies employed in this paper consistently predict the barrier height of reaction (1) to be within the range 2.16-5.11 kcal mol-1, somewhat higher than the experimental value of 2.0 kcal mol-1.

The Gas‐Phase Reaction between O3 and HO Radical: A Theoretical Study

“…mol À1 , respectively (DE + DZPE relative to C1, see footnote [e] of Table 1), which compare well with the results reported by Peiró-García and Nebot-Gil, also computed at the CCSD(T) level. [17] However, the values of the T1 diagnostic of the corresponding CCSD wavefunction (0.0522 and 0.0437, respectively) are very high, thus confirming that the single-determinantbased methods are not appropriate. Therefore, we employed the multireference CASPT2-based method, and the computed energy barriers for TS1 and TS2 are 1.80 and 2.26 kcal.…”

“…[24] A schematic description of the composition of these active spaces is given in the Supporting Information. The effects of the dynamical correlation energy on the relative stability of the stationary points was considered by carrying out CASPT2 [25] single-point calculations based on a common CASSCFA C H T U N G T R E N N U N G (17,14) reference function with the 6-311 + GA C H T U N G T R E N N U N G (2df,2p) basis set.…”

“…The existence of this HO 4 intermediate is controversial; it was suggested by Varandas and Zhang, [12] but Peiró-García and Nebot-Gil [17] as well as Ryabinkin et al [18] concluded that it does not exist. Therefore, we have performed an additional computational effort to elucidate the possible existence of this tetraoxide radical.…”

“…[13][14][15][16] On the other hand, Peiró-García and NebotGil [17] carried out a theoretical ab initio study employing singledeterminant-based methods, in which the existence of a prereactive complex was not mentioned, and concluded that the HO 4 intermediate does not exist, so that the reaction takes place in a single step. Moreover, Ryabinkin et al reported an ab initio study on the title reaction and also concluded that HO 4 does not exist.…”

Theoretical study of reaction mechanism for Se + O3

“…The roles and applications of ozone in chemical reactions are essential and important. The reaction of ozone with other species is one of the best investigated chemical reactions which have been reported in many researches published in the recent years [6][7][8][9][10][11][12].…”