The Hydration of Trifluoroacetic Acid from 0 to 298 K

Trifluoroacetic acid (TFA), the most atmospherically abundant perfluorocarbocylic acid, is a molecule of increasing environmental and biological significance. In this paper, we examine TFA's role in new particle formation (NPF), a critical yet lesser-understood step in cloud formation in which aerosols that act as cloud condensation nuclei are formed. We used conformational sampling to find low-energy structures for TFA-<i>n</i>H₂O (<i>n</i> = 1-8) clusters and determined accurate DLPNO-CCSD(T)/haug-cc-pV5Z//ωB97X-D/6-31++G** enthalpies at 0 K and Gibbs free energies at 216.65, 273.15, and 298.15 K. Then, atmospheric concentrations were determined at relevant atmospheric temperatures. Rotational constants for the lowest energy <i>n</i> = 1-3 structures corroborate existing microwave spectroscopic data, validating our methodology. Additionally, spectroscopic properties for <i>n</i> = 4-8 structures were identified for comparison with future experimental findings. All lowest energy structures were found to have neutral, rather than ion-pair monomers. Near Earth's surface, we predict significant concentrations of <i>n</i> = 1-2 clusters (2.06 × 10⁵ molecules cm^-3 and 1.13 × 10⁴, respectively); however, the absence of larger clusters indicates that TFA likely serves a negligible role in NPF.