Conformational dynamics of perfluorooctanoic acid (PFOA) studied by molecular rotational resonance (MRR) spectroscopy

Highlights: • Highly-resolved rotational signature of perfluorooctanoic acid (PFOA). • Conformational space of perfluorooctanoic acid (PFOA). • Insights into the stability and isomeric pathways between lowest-energy set of conformers. We report the rotational spectrum of perfluorooctanoic acid (PFOA) recorded using a broadband MRR spectrometer. The observed spectrum shows well-resolved rotational patterns due to MRR's sensitivity to conformational changes. With the aid of quantum chemistry calculations, six conformers observed in our pulsed-jet experiment have been assigned. Their conformational structures were identified by comparing their rotational constants and dipole moment orientation. We find that the perfluorinated carbon chain adopts a helical configuration to maximize the separation between fluorine atoms. We present calculations of the barriers to conformational isomerization between the low-energy conformers, including the possibility of reversing the helix direction.