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.

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.

Despite recent encouraging developments, achieving efficient blue perovskite light-emitting diodes (PeLEDs) have been widely considered a critical challenge. The efficiency breakthrough only occurred in the sky-blue region, and the device performance of pure-blue and deep-blue PeLEDs lags far behind those of their sky-blue counterparts. To avoid the negative effects associated with dimensionality reduction and excess chloride typically needed to achieve deep-blue emission, here we demonstrate guanidine (GA+)-induced deep-blue (∼457 nm) perovskite emitters enabling spectrally stable PeLEDs with a record external quantum efficiency (EQE) over 3.41% through a combination of quasi-2D perovskites and halide engineering. Owing to the presence of GA+, even a small inclusion of chloride ions is sufficient for generating deep-blue electroluminescence (EL), in clear contrast to the previously reported deep-blue PeLEDs with significant chloride inclusion that negatively affects spectral stability. Based on the carrier dynamics analysis and theoretical calculation, GA+ is found to stabilize the low-dimensional species during annealing, retarding the cascade energy transfer and facilitating the deep-blue EL. Our findings open a potential third route to achieve deep-blue PeLEDs beyond the conventional methods of dimensionality reduction and excessive chloride incorporation.

Kinetics provides the fundamental parameters for elucidating sources and sinks of key atmospheric species and for atmospheric modeling more generally. Obtaining quantitative kinetics in the laboratory for the full range of atmospheric temperatures and pressures is quite difficult. Here, we use computational chemistry to obtain quantitative rate constants for the reactions of HO 2 with HCHO, CH 3 CHO, and CF 3 CHO. First, we calculate the high-pressure-limit rate constants by using a duallevel strategy that combines conventional transition state theory using a high level of electronic structure wave function theory with canonical variational transition state theory including smallcurvature tunneling using density functional theory. The wavefunction level is beyond-CCSD(T) for HCHO and CCSD(T)-F12a (Level-A) for XCHO (X = CH 3 , CF 3 ), and the density functional (Level-B) is specifically validated for these reactions. Then, we calculate the pressure-dependent rate constants by using system-specific quantum RRK theory (SS-QRRK) and also by an energy-grained master equation. The two treatments of the pressure dependence agree well. We find that the Level-A//Level-B method gives good agreement with CCSDTQ(P)/CBS. We also find that anharmonicity is an important factor that increases the rate constants of all three reactions. We find that the HO 2 + HCHO reaction has a significant dependence on pressure, but the HO 2 + CF 3 CHO reaction is almost independent of pressure. Our findings show that the HO 2 + HCHO reaction makes important contribution to the sink for HCHO, and the HO 2 + CF 3 CHO reaction is the dominant sink for CF 3 CHO in the atmosphere.

Criegee intermediates are important oxidants produced in the ozonolysis of alkenes in the atmosphere. Quantitative kinetics of the reactions of Criegee intermediates are required for atmospheric modeling. However, the experimental...