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

Abstract

Criegee intermediates are important atmospheric oxidants, and quantitative kinetics for stabilized Criegee intermediates are key parameters for atmospheric modeling but are still limited. Here we report barriers and rate constants for unimolecular reactions of s-cis-syn-acrolein oxide (scsAO), in which the vinyl group makes it a prototype for Criegee intermediates produced in the ozonolysis of isoprene. We find that the MN15-L and M06-2X density functionals have CCSD­(T)/CBS accuracy for the unimolecular cyclization and stereoisomerization of scsAO. We calculated high-pressure-limit rate constants by the dual-level strategy that combines (a) high-level wave function-based conventional transition-state theory (which includes coupled-cluster calculations with quasiperturbative inclusion of quadruple excitations because of the strongly multiconfigurational character of the electronic wave function) and (b) canonical variational transition-state theory with small-curvature tunneling based on a validated density functional. We calculated pressure-dependent rate constants both by system-specific quantum Rice–Ramsperger–Kassel theory and by solving the master equation. We report rate constants for unimolecular reactions of scsAO over the full range of atmospheric temperature and pressure. We found that the unimolecular reaction rates of this larger-than-previously studied Criegee intermediate depend significantly on pressure. Particularly, we found that falloff effects decrease the effective unimolecular cyclization rate constant of scsAO by about a factor of 3, but the unimolecular reaction is still the dominant atmospheric sink for scsAO at low altitudes. The large falloff caused by the inclusion of the stereoisomerization channel in the master equation calculations has broad implications for mechanistic analysis of reactions with competitive internal rotations that can produce stable rotamers.

Reaction of SO3 with HONO2 and Implications for Sulfur Partitioning in the Atmosphere

“…We have investigated R4 using the dual-level rate strategy developed by our group that combines transition state theory at the W2X//DF-CCSD­(T)-F12b , /jun′-cc-pVDZ level, with variational transition state theory including small-curvature tunneling , at the M08-HX/MG3S , level. The jun′-cc-pVDZ basis set is a revision of jun-cc-pVDZ, which is similar to the jun′-cc-pVTZ basis set from jun-cc-pVTZ in our previous investigation . The pressure-dependent rate constants were calculated using the system-specific quantum Rice–Ramsperger–Kassel (SS-QRRK) theory; the validity of this method was further shown by master equation (ME) calculations in the SI (Supporting information).…”

Quantitative Kinetics of the Reaction between CH2OO and H2O2 in the Atmosphere

“…Therefore, Table S3 also shows that the calculated zero-point vibrational energies are reliable at the DF-CCSD­(T)-F12b/jun′-cc-pVDZ level. However, we have noted earlier that the quantitative determination of zero-point vibrational energies for some Criegee reactions is extremely difficult . We also note that MN15-L/MG3S, M11-L/MG3S, and B3LYP/MG3S have larger MUDs at least above 0.5 kcal/mol (see Table S3).…”

“…However, we have noted earlier that the quantitative determination of zero-point vibrational energies for some Criegee reactions is extremely difficult. 108 We also note that MN15-L/MG3S, M11-L/MG3S, and B3LYP/MG3S have larger MUDs at least above 0.5 kcal/mol (see Table S3). This again reflects that it is difficult choosing a reliable functional method for obtaining quantitative zero-point vibrational energies at 0 K.…”

“…Previous studies have shown that post-CCSD(T) calculations are required to obtain quantitative barrier heights in Criegee reactions. 40,56,92,108,109 Here, the calculated results show that the contribution of post-CCSD(T) calculations is approximately 0.6 kcal/mol for the enthalpies of activation at 0 K in the CH 2 OO + H 2 O 2 reaction because the MUD of W2X/ CCSD(T)-F2a/cc-pVTZ-F12 is 0.58 kcal/mol, compared to W3X-L/CCSD(T)-F2a/cc-pVTZ-F12 in Table 1. In addition, the contribution of post-CCSD(T) calculations is more significant for the enthalpies of reaction at 0 K than the enthalpies of activation at 0 K in Table S5.…”

Important Routes for Methanediol Formation by Formaldehyde Hydrolysis Catalyzed by Iodic Acid and for the Contribution to an Iodic Acid Sink by the Reaction of Formaldehyde with Iodic Acid Catalyzed by Atmospheric Water

“…Moreover, post-CCSD­(T) calculations are required to obtain quantitative barrier heights due to these slightly large T1 diagnostic values . However, our previous investigations have shown that post-CCSD­(T) calculations contribute to only approximately 0.5 kcal/mol. − Additionally, computational costs are prohibitive for post-CCSD­(T) calculations for the reaction systems investigated here. Therefore, we ignore the post-CCSD­(T) calculations in this work.…”