Gas-Phase Ozone Reactions with a Structurally Diverse Set of Molecules: Barrier Heights and Reaction Energies Evaluated by Coupled Cluster and Density Functional Theory Calculations

Abstract

Reactions with ozone transform organic and inorganic molecules in water treatment systems as well as in atmospheric chemistry, either in the aqueous phase, at gas/ particle interfaces, or in the gas phase. Computed thermokinetic data can be used to estimate the reactivities of molecules toward ozone in cases where no experimental data are available. Although the gas-phase reactivity of olefins with ozone has been characterized extensively in the literature, this is not the case for the richer chemistry of ozone with polar molecules, which occurs in the aqueous phase or in microhydrated environments. Here, we selected a number of model reactions with small molecules (ethene, ethyne, hydrogen cyanide, hydrogen chloride, ammonia, bromide, and trimethylamine) to study the accuracy of different quantum chemical methods for describing the reactivities of these molecules with ozone. We calculated benchmark electronic energies of gas-phase reactions of these systems with singlereference coupled cluster (CC) theory. These benchmark results for the binding energy in the van der Waals complex, the energy of the transition structure, and the reaction energy were estimated to be accurate within 1−2 kcal mol −1 . Singlet oxygen ( 1 O 2 ) is a common product of ozone reactions. Coupled cluster calculations with up to perturbative quadruples (CCSDT(Q)) were needed to obtain reaction energies accurate within 1 kcal mol −1 when this species was involved. In (micro)hydrated environments or at interfaces, coupled cluster methods are prohibitively expensive in most cases. We tested the suitability of some contemporary density functional theory (DFT) methods to reproduce the benchmark electronic energy differences. Range-separated functionals were found to be promising candidates to estimate forward barrier heights, with LC-ωPBE rivaling the accuracy of CCSD(T). For energies of reaction, however, DFT methods exhibited large systematic errors, depending on their fraction of orbital exchange. This was found to worsen when 1 O 2 is a product, and no safe recommendation can be given for DFT reaction energies in such cases.

Dipolar 1,3‐cycloaddition of thioformaldehydeS‐methylide (CH2SCH2) to ethylene and acetylene. A comparison with (valence) isoelectronicO3,SO2,CH2OOandCH2SO

“…In the case of the reaction of O 3 with ACE, Cramer et al110 determined a value of 9.28 kcal mol À1 at the CCSD(T)/CBS limit. The most recent study by Trogolo et al111 obtained a best estimate of 7.65 kcal mol À1 , which agrees nicely with our results (7.70 kcal mol À1 at the SVECV-f12 and 7.80 at the jun-ChS levels of theory). From this analysis, it is clear that our composite protocols are able to represent very well the reaction of O 3 with double and triple bonds, irrespective of the multireference character of its ground state.…”

Reactions of pyrrole, imidazole, and pyrazole with ozone: kinetics and mechanisms

“…49 The thermodynamic feasibility of the proposed reactions was tested with free energy calculations, along with the connectivity of intermediates on the potential energy surface. 50 The LC-ωPBE 51 functional was chosen for the description of the initial ozone reactivity 52 and for its generally sound description of the thermochemistry. 51 The SMD implicit solvation model was used.…”

“…Such concerted cycloadditions have been studied in depth for reactions of simple unsaturated hydrocarbons (e.g., ethene and ethyne) with ozone in aqueous phase by a recent quantum chemical study. 52 The pyrrole-nitrogen is excluded as a possible attack site, because its lone electron pair is delocalized in the π-system of the ring. A recent study demonstrated that the addition of atomic oxygen on the pyrrole-N is very unlikely compared to the addition on C, based on quantum chemical computations of the energies of the corresponding products (+39 kcal mol −1 for N-addition and −19 kcal mol −1 for C2addition).…”

Highly Accurate CCSDT(Q)/CBS Reaction Barrier Heights for a Diverse Set of Transition Structures: Basis Set Convergence and Cost-Effective Approaches for Estimating Post-CCSD(T) Contributions

“…Normally, the CCSDT(Q) method is used for investigating relatively small transition structures (TSs) with pronounced multireference character. For instance, for reactions involving oxygen-rich species 25,26,27,28,29,30,31,32,33,34,35,36,37 and other small TSs. 38,39,40,41,42,43,44,45,46,47 The aim of the present work is to provide a systematic examination of basis set convergence of post-CCSD contributions (up to CCSDT(Q)) for a diverse set of reaction barrier heights.…”