Pyrolysis of Trifluoroacetic Acid and Trifluoroacetic Anhydride Studied with Mass Spectrometry and Synchrotron Radiation: Decomposition and Free Radical Formation

Abstract

The remediation strategies for accumulated polyfluoroalkyl substances (PFAS) are a subject of great concern in environmental science. In this study, the thermal decomposition of trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAN), taken as models of PFAS, were explored. Imaging photoelectron photoion coincidence (iPEPICO) spectroscopy was used to detect pyrolysis products from room temperature to 1000 °C under dilute conditions. The observed pyrolysis products of each molecule were CO, CO2, CF2, and CF2O (and CF3 for TFAN), with some species reflecting unimolecular rearrangement prior to dissociation. Electronic structure calculations using density functional theory and the SVECV-F12 composite method were employed to evaluate the energy of the different decomposition channels. The results show the advantage of exploring the pyrolysis under dilute conditions to catch the first stages of unimolecular dissociation of these molecules for the first time.