Tropospheric degradation of 2-fluoropropene (CH3CFCH2) initiated by hydroxyl radical: Reaction mechanisms, kinetics and atmospheric implications from DFT study.

Degradation of hydrofluoro-olefins (HFOs) with oxidants plays a significant role in the troposphere. Thus, we have investigated detail theoretical calculations of hydroxyl radical (•OH) initiated oxidation of 2-fluoropropene (CH3CFCH2) using M06-2X/6-311++G(d,p) level of theory. Here, we have considered different possible H-abstraction and OH addition for the degradation of CH3CFCH2 molecule. The potential energy analysis shows that OH-addition channels are more dominant than H-abstraction channels. The calculated reaction enthalpies (ΔrH°) and Gibbs free energies (ΔrG°) also suggest that OH-addition reaction channels are more favourable than H-abstraction channels. The overall rate coefficients for CH3CFCH2 + •OH reaction is calculated within the temperature range of 250-450 K. The observed overall rate coefficient (2.01 × 10-11 cm3 molecule-1 s-1) at 298 K for the titled reaction is found to be in good agreement with the earlier reported experimental rate coefficient. The calculated percentage branching ratio shows that the contribution of OH-addition to α-carbon and β-carbon of CH3CFCH2 molecule are 85.10% and 14.20% to the overall rate coefficient while H-abstractions have a negligible contribution. Based on the kinetics calculations, the atmospheric lifetime of the titled molecule is found to be 0.6 days. Further, we have also explored the degradation pathways of OH-addition product radicals and found acetyl fluoride (CH3CFO) and formaldehyde (HCHO) are the end degradation products.