The electronic spectra of trifluoroacetic acid and chlorodifluoroacetic acid in the 4.5 – 10.8 eV photon energy region

Synchrotron radiation has been used to record for the first time absolute vacuum ultraviolet photoabsorption cross-sections of trifluoroacetic acid (TFA) and chlorodifluoroacetic acid (CDFA) in the 4.5–10.8 eV energy range. In order to further our knowledge of the major electronic transitions and thus help interpret the photoabsorption data, theoretical calculations using time-dependent density functional theory (TD-DFT) level have been performed. These calculations have provided important information on the nature of the excited electronic states which have been assigned to valence, mixed valence-Rydberg and Rydberg transitions. Due to the lack of any information about CDFA ionic states, we also provide Equation-of-Motion Coupled-Cluster Single and Doubles (EOM-CCSD) vertical ionisation energies. Photolysis lifetimes in the Earth's atmosphere for both chemical compounds have also been estimated from the absolute photoabsorption cross-section data.