Experimental and Theoretical Investigation of the Reaction between the Simplest Criegee Intermediate and Hydrogen...

Criegee intermediates play a central role in the formation of secondary organic aerosols in heavily forested regions. These highly reactive species are capable of oxidizing a wide range of atmospheric compounds. While quantum chemical calculations often provide the relevant rate coefficients, computational methods must be validated against benchmark systems which are simple enough to investigate both experimentally and with high-level theory. In this work, we report the kinetics of the CH₂OO + HF reaction, using a multipass UV-vis spectrometer coupled to a pulsed-laser photolysis flow reactor. The rate coefficient was found to be k₃ = (1.34 ± 0.17) × 10^-12 cm³ s^-1 at 293 K with a negligible pressure effect across 30-80 Torr and was with a negative activation energy of E_a = (-1.69 ± 0.36) kcal mol^-1 across 245-293 K. These results were reproduced within experimental uncertainty using semiclassical transition state theory with energies and rovibrational parameters calculated by a high-level electronic structure method mHEAT+-345Q. We identified that the effects of connected quadruples and tunneling are essential for calculating the CH₂OO + HF rate coefficients, highlighting the role of high-order correlation in achieving high-accuracy kinetic predictions for reactions of Criegee intermediates.