Atmospheric Kinetics: Bimolecular Reactions of Carbonyl Oxide by a Triple-Level Strategy

Abstract

Criegee intermediates in the atmosphere serve as oxidizing agents to initiate aerosol formation, which are particularly important for atmospheric modeling, and understanding their kinetics is one of the current outstanding challenges in climate change modeling. Because experimental kinetics are still limited, we must rely on theory for the complete picture, but obtaining absolute rates from theory is a formidable task. Here, we report the bimolecular reaction kinetics of carbonyl oxide with ammonia, hydrogen sulfide, formaldehyde, and water dimer by designing a triple-level strategy that combines (i) benchmark results close to the complete-basis limit of coupled-cluster theory with the single, double, triple, and quadruple excitations (CCSDTQ/CBS), (ii) a new hybrid meta density functional (M06CR) specifically optimized for reactions of Criegee intermediates, and (iii) variational transition-state theory with both variable rection coordinates and optimized reaction paths, with multidimensional tunneling, and with pressure effects. For (i) we have found that quadruple excitations are required to obtain quantitative reaction barriers, and we designed new composite methods and strategies to reach CCSDTQ/CBS accuracy. The present findings show that (i) the CH 2 OO + HCHO reaction can make an important contribution to the sink of HCHO under wide atmospheric conditions in the gas phase and that (ii) CH 2 OO + (H 2 O) 2 dominates over the CH 2 OO + H 2 O reaction below 10 km.

Temperature-dependent kinetics of the atmospheric reaction between CH2OO and acetone

“…To choose the lower level, we tested the MN15-L, 72 M11-L, 73 M06-2X, 74 and M06CR 61 density functionals with the MG3S 75 basis set. We choose M11-L from among these trial functionals because it showed best agreement with the higher-level calculations.…”

“…Furthermore, previous investigations have shown that higher excitation levels than CCSD(T) (we call them beyond-CCSD(T) calculations) are necessary for reliable results due to the strong multireference characters of Criegee intermediates. [59][60][61][62][63][64][65] In this article, we use our recently developed dual-level rateconstant strategy 60,[66][67][68] and system-specific quantum Rice-Ramsperger-Kassel theory (SS-QRRK) to obtain rate constants for the CH 2 OO + CH 3 C(O)CH 3 reaction under atmospheric temperature and pressure conditions. We use the W3X-L composite method that goes beyond CCSD(T) as the higher level in the dual-level calculations.…”

“…Furthermore, previous investigations have shown that higher excitation levels than CCSD(T) (we call them beyond-CCSD(T) calculations) are necessary for reliable results due to the strong multireference characters of Criegee intermediates. 59–65…”

“…The W3X-L calculations were carried out at DF-CCSD(T)-F12b 69 /jun-cc-pVDZ 70 geometries; our previous investigations showed that this combination can yield accurate barrier heights. 61…”

Large Pressure Effects Caused by Internal Rotation in the s-cis-syn-Acrolein Stabilized Criegee Intermediate at Tropospheric Temperature and Pressure

“…To select a method for direct dynamics calculations, we used the benchmark to test three exchange-correlation functionals: MN15-L, M06-2X, and M06CR–in all three cases with the MG3S basis set. As a result of these tests, we selected MN15-L/MG3S for the cyclization reaction and M06-2X/MG3S for the stereoisomerization reaction.…”