Published: September 08, 2011 r2011 American Chemical Society 10911 dx.doi.org/10.1021/jp205734h | J. Phys. Chem. A 2011, 115, 10911–10919 ARTICLE pubs.acs.org/JPCA Kinetics and Thermodynamics of Limonene Ozonolysis Leonardo Baptista,* ,† Rene Pfeifer, ‡ Edilson Clement da Silva, ‡ and Graciela Arbilla ‡ † Faculdade de Tecnologia, Departamento de Química e Ambiental, Universidade Estadual do Rio de Janeiro, Rodovia Presidente Dutra Km 298, Resende, RJ, Brazil ‡ Instituto de Química, Universidade Federal do Rio de Janeiro, Avenida Athos da Silveira Ramos, 149 Bloco A, 4° andar CEP 21941-909 Cidade Universit  aria, Rio de Janeiro, RJ, Brazil b S Supporting Information ’ INTRODUCTION Although the potential for aerosol formation of biogenically emitted compounds was proposed in 1960, 1 the extent of the contributions from this vast source to aerosol loading is still unknown. Finlayson-Pitts 2 has pointed out how several problems that may be solved to obtain a better understanding of atmo- spheric chemistry to predict climate change and impacts on air quality. The important issues that are being investigated include the formation of molecules that may act as cloud condensation nuclei (CCN) and the physical chemistry of the nucleation process. Zhao et al. 3 have shown that the ability to form hydrogen bonds between organic molecules and inorganic species in the atmosphere is important for the formation of molecular clusters. According to this study, the hydrogen bond formed between organic molecules and inorganic molecules, such as sulfuric acid, lowers the hydrophobic character of the organic molecules promoting the growth of particles in the atmosphere leading to secondary organic aerosol (SOA) formation. The oxidation products of monoterpenes emitted in the atmosphere may participate in the formation of SOAs 4 due to reactions with OH radicals and O 3 that lead to water-soluble species, which can act as CCN. 5 There is great interest in the ozonolysis of monoterpenes because these reactions may affect the formation of urban SOAs. Currently, the accepted mechanism for ozonolysis was pro- posed by Criegee. 6 The initial step involves the cycloaddition of ozone with a double bond forming the trioxolane intermediate known as the primary ozonide (POZ). This reaction is concerted and highly exothermic (by approximately 47À64 kcal mol À1 ). The excess energy may be retained by the POZ leading to a rapid decomposition of the trioxolane ring resulting from homolytic cleavage of the CÀC and OÀO bonds. This cleavage leads to two new molecules. The first is a primary carbonyl, and the second is a highly reactive carbonyl oxide intermediate, known as a Criegee intermediate (CI), that was observed for the first time in a recent photoionization study. 7 The most recent theoretical studies de- scribe the electronic structure of the CI as zwitterionic. 8 The CI possesses excess energy leading to unimolecular reactions or stabilization from collisions with the surrounding gas, which allows the intermediate to react by the hydroperoxy or ester channel. 6 Many experimental and theoretical studies have been focused on describing the ozonolysis of terpenes, determining the ozonolysis products and evaluating the thermodynamic and kinetic parameters of ozonolysis. 9À17 Zhang et al. 18 calculated the potential energy surface (PES) for the reaction of O 3 with α- and β-pinene using density functional methods (DFT). The dynamics of the reaction were analyzed by RRKM theory and by solving the master equation. 19 They observed that the addition of O 3 to double bonds is highly exothermic and hydrogen migration to the hydroperoxide represents the major pathway for dioxirane ring closure. The master equation study showed significant stabilization of the high energy Criegee intermediate formed during the oxidation process from collision processes. Nguyen et al. 20 extended the work of Zhang et al. 18 to β-pinene ozonolysis using DFT, CASPT2, and basis set extrapolation methods followed by statistical kinetic analysis. The calculated Arrhenius parameters, k tot (T) = 1.1 Â 10 À22 Â T 2.66 Â exp(À888 K/T) cm 3 molecule À1 s À1 , correctly reproduced the slightly Received: November 21, 2010 Revised: August 30, 2011 ABSTRACT: Using density functional methods, the initial reaction steps of limonene ozonolysis have been investigated with a focus on primary ozonide formation and its decomposi- tion to Criegee intermediates and carbonyl compounds. The ozonide formation is highly exothermic, and the decomposition channels have similar free energies of activation, ΔG ‡ , indicating that there is no primary pathway for ozonide decomposition. Assuming that ozonide formation is the rate limiting step, the theoretical rate coefficient, k = 1.6 Â 10 À16 molecule À1 cm 3 s À1 , evaluated at the CCSD(T)/6-31G(d,p)//BHandHLYP/cc-pvdz level and 298.15 K for d-limonene is in good agreement with the experimental value, k exp = 3.3 Â 10 À16 molecule À1 cm 3 s À1 . The theoretical Arrhenius expression is also in good agreement with experimental results.