Atmospheric Fate of CF3CF2CH2OCH3 (HFE-365mcf3) Initiated by OH Radicals and Cl Atoms: Insights into the Mechanisms, Conformer-Weighted Kinetics, and Atmospheric Loss Processes

Abstract

Hydrofluoroethers, such as 1,1,1,2,2-pentafluoro-3-methoxypropane (HFE-365mcf3), are widely used as alternatives to various ozone-depleting substances, yet a molecular level understanding of their tropospheric oxidation chemistry remains incomplete. Previous experimental studies of HFE-356mcf3 focused mainly on the total rate coefficients and stable products, providing limited insights into site-specific pathways, conformational contributions, or the fate of the initially formed radicals. Therefore, in this work, we present a comprehensive theoretical investigation of the atmospheric oxidation of HFE-365mcf3 with •OH and Cl atoms. The study began with conformational analysis of the titled molecule using the conformer-rotamer-ensemble sampling tool (CREST), followed by conformer-weighted kinetic calculations. The rate coefficients were computed using the variational transition-state theory (VTST) with Eckart tunneling corrections over the 200 - 400 K temperature range. •OH predominantly abstracts from the methylene carbon due to the captodative effect, while Cl abstracts from the methoxy carbon due to steric effects, validated by NBO analysis. Also, Cl atoms abstract two-orders of magnitude faster than •OH, indicating their importance in governing rates and subsequent radical degradation. Moreover, the atmospheric lifetime, radiative efficiency, and GWP100 were computed to be 43.5 days, 0.055 W m^-2 ppb^-1, and 2.47, respectively. Additionally, the subsequent degradation studies of the major product radicals in the presence of O₂ and NO_x have been carried out. These results indicate that HFE-365mcf3 is a short-lived and low-impact CFC alternative with minimal environmental impact. Thus, this work provides suitable insights into the thermodynamics and kinetics necessary to assess the atmospheric fate and sustainability of HFE-365mcf3 as a CFC alternative.