2025/07/25 by Yin, Cangtao, Käser, Silvan, Upadhyay, Meenu +1
#Chemical Physics (physics.chem-ph) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2507.18964
The end-to-end dynamics of the smallest energized Criegee intermediate, H2COO, was characterized for vibrational excitation close to and a few kcal/mol above the barrier for hydrogen transfer. From an aggregate of at least 5 μs of molecular dynamics simulations using a neural network-representation of CASPT2/aug-cc-pVTZ reference data, the branching ratios into molecular products HCO+OH, CO2+H2, or H2O+CO was quantitatively determined. Consistent with earlier calculations and recent experiments, decay into HCO+OH was found to be rare (∼ 2 %) whereas the other two molecular product channels are accessed with fractions of ∼ 30 % and ∼ 20 %, respectively. On the 1 ns time scale, which was the length of an individual MD simulation, more than 40 % of the systems remain in the reactant state due to partial intramolecular vibrational redistribution (IVR). Formation of CO2+H2 occurs through a bifurcating pathway, one of which passes through formic acid whereas the more probable route connects the di-radical OCH2O with the product through a low-lying transition state. Notably, none of the intermediates along the pathway accumulate and their maximum concentration always remains well below 5 %. This work demonstrates that atomistic simulations with global reactive machine-learned energy functions provide a quantitative understanding of the chemistry and reaction dynamics for atmospheric reactions in the gas phase.