The gas-phase ozonolysis of β-caryophyllene (C15H24). Part II: A theoretical study

Abstract

The O(3)-initiated oxidation of beta-caryophyllene, a sesquiterpene emitted in forested areas, was theoretically characterized for the first time using DFT quantum chemical calculations combined with statistical kinetic RRKM/master equation analysis and variational transition state theory. O(3)-Addition occurs primarily, >95%, on the endocyclic double bond without a barrier, leading to a total rate coefficient of 8.3 x 10(-24) T(3.05) exp(1028 K/T) cm(3) molecule(-1) s(-1), with a slight negative T-dependence. Thermal and chemically activated unimolecular reactions following this addition, including the so-called ester and hydroperoxide channels, and internal formation of the secondary ozonide, where characterized and quantified; a newly discovered reaction pathway through intersystem crossing from a dioxirane to a triplet bis(oxy) biradical intermediate is incorporated in the mechanism. The first generation product distribution at 298 K is predicted as 74% stabilized Criegee intermediates (CI), 8% OH radicals together with vinoxy-type 2-oxo alkyl radical co-products, 8% acids, 0.3% esters, and 9% CO(2) with two alkyl radical co-products. The thermalized CI can convert to the secondary ozonide in many reaction conditions, in particular the atmosphere; secondary ozonides are thus expected as dominant products of the beta-caryophyllene ozonolysis. These results are consistent with the experimental data presented in the accompanying paper (Part I). The temperature dependence and uncertainties of the product distribution are discussed. The high molecular weight oxygenated products, including beta-caryophyllonic acid and secondary ozonides, are expected to contribute to secondary organic aerosol formation.

Communication: Thermal unimolecular decomposition of syn-CH3CHOO: A kinetic study

“…The calculated barrier of 72 kJ/mol agrees well with a value of 71.5 kJ/mol 25 that has been published very recently by Fang et al, 25 using a similarly high accuracy level of theory. The mHEAT value also lies within the range of 67-75 kJ/mol 6,25,40 reported earlier in the literature. It should be noted that the calculated barrier is higher than the experimental estimate of ≤67 kJ/mol.…”

“…Syn-CH 3 CHOO could also proceed through a ring-closure step leading to methyl-dioxirane, but this pathway has a significantly higher barrier (100-110 kJ/mol 25,[38][39][40] ). Such a cyclization cannot compete with the 1,4 H-shift under atmospheric conditions and will not be considered further.…”

Development and chamber evaluation of the MCM v3.2 degradation scheme for β-caryophyllene

“…β-caryophyllene has received particular attention, being one of the most reactive and abundant sesquiterpenes, and SOA yields have been reported in a number of ozonolysis and photo-oxidation studies (Hoffmann et al, 1997;Griffin et al, 1999;Jaoui et al, 2003;Lee et al 2006a, b;Winterhalter et al, 2009;Alfarra et al, 2012). As a result, its atmospheric degradation has been the subject of a number of experimental and theoretical mechanistic appraisals (Calogirou et al, 1997;Jaoui et al, 2003;Lee et al, 2006b;Kanawati et al, 2008;Winterhalter et al, 2009;Nguyen et al, 2009;Zhao et al, 2010;Li et al, 2011;Chan et al, 2011), and several established oxidation products have been used in tracer studies to show that β-caryophyllene-derived SOA makes potentially important contributions to ambient fine particulate matter at a number of locations Parshintsev et al 2008).…”

“…The general methodology of mechanism construction was based on the rules described in detail by Jenkin et al (1997) and Saunders et al (2003), with the chemistry adjusted and augmented (in certain areas substantially) to represent information reported in a number of experimental and theoretical studies of β-caryophyllene degradation available at the time of construction (Shu and Atkinson, 1994;Calogirou et al, 1997;Atkinson and Arey, 2003;Jaoui et al, 2003;Lee et al, 2006a, b;Kanawati et al, 2008;Nguyen et al, 2009). The complete mechansim consists of 1626 reactions of 591 closed-shell and radical species.…”

UV-spectroscopy, electronic structure and ozonolytic reactivity of sesquiterpenes: a theoretical study

“…Previous studies using ultraviolet photo electron spectroscopy (UPS) combined with theoretical calculation examined the ionization cross sections and first ionization energies for some sesquiterpenes, but failed to obtain the complete picture of a potentially significant part of atmospheric chemistry and environmental effects of these materials [22][23][24]. Experimental studies of ozonolysis of sesquiterpenes, which showed that semi-volatile products were produced in gas-phase reactions, were limited to individual configurations [13,21]. Currently, no laboratory measurements and simulation have been performed to explain the field-based results that sesquiterpenes exerted negative effects on climate change because of their absorption in UV region [14,17,32].…”